River and groundwater contamination is generally caused by chemical fertilizer, manure and nitrogenous waste products, all containing nitrogen, used for both agricultural and industrial purposes [23]. Therefore, contamination can affect rural, semi-urban and industrialized areas. In the case here analyzed, the source of nitrates is the deposit of fecal matters. As a consequence of dry climate conditions and pastoralist-related livelihoods, northern Kenya mostly features the availability of open shallow water sources, sometimes found exactly in the riverbed (e.g., open shallow wells) [24]. The seasonal rainfall pattern causes the activation of nitrate contamination hazard. In the case of shallow wells, seasonal streams have an intermittent runoff and pastoralists can let their livestock graze near the well while waiting for watering, allowing the deposit of fecal matter directly into the watercourse. For this reason, there may be direct or indirect contamination of the water source depending on whether "fecal matter is deposited directly into waterways or so close that the potential for wash-in is very high, or via surface runoff and subsurface seepage or drainage" [25]. Although there is certainly a direct pathway of fecal matter in the well during the wet season, it is probable that another means of contamination is nitrate percolation through the permeable surface to the subsurface water reservoir. Nitrate percolation activates during rain events without adequate soil contact time for efficient denitrification and retention [26]. Therefore, soil characteristics modelling is crucial for nitrate vulnerability assessment, but its role in contamination dynamics is not known due to the uniqueness of this means of contamination. Studies in New Zealand focus on nitrate movements along a shallow groundwater flow path in a riparian wetland [26] and on estimating fecal yields from agricultural catchments for water quality purposes [27–29]. Another study in Minnesota assesses private wells vulnerability to nitrate leaching, focusing on future extreme rainfall estimates and floodand nitrate-sensitive well identification [30]. Optimal tools for shallow groundwater risk assessment are the DRASTIC and GOD methods, widely applied in arid contexts [31–35]. The DRASTIC method is considered as one that does not need extensive, site-specific pollution data, but able to provide a solution for evaluating the vulnerability to pollution of groundwater based on known hydrogeological parameters (depth to groundwater, net recharge, aquifer media, soil media, general topography or slope, vadose zone and hydraulic conductivity of the aquifer). The GOD model, indeed, is based on only three parameters (groundwater confinement, overlying strata, and depth to groundwater. However, data availability in a developed context, where the research on nitrate pollution of shallow groundwater is well-developed, is different from a Global South context. In Kenya, these types of data are not available or partially available from project output (difficult to find and obtain) or from a global dataset (based on estimations and not fully reliable). Alternative methods [36,37] require the characteristics of the hazard, i.e., nitrate source yields which are also unknown. In general, therefore, in North Horr Sub-County high spatial and high temporal resolution data, as well as point data, are scarce. Thus, in this paper, a flexible methodology was applied focused on the vulnerability assessment in a scant data context. Since the vulnerability is multidimensional, it is almost impossible to define a universal measurement methodology [38] as well as a finite set of potential indicators [39]. Therefore, using the indications of the Intergovernmental Panel on Climate Change (IPCC) [40,41], nitrate contamination specific sub-indicators of exposure, sensitivity and adaptive capacity were identified and combined in order to obtain the indicator of vulnerability for nitrate contamination hazard in the area. The quantitative approach used in this research to evaluate the vulnerability in the North Horr area is based on a tested methodology [42] applied, for the first time, in a scant data context. Although both qualitative and quantitative methods for the evaluation of the vulnerability from nitrate in open shallow water sources are possible, few studies have tried to tackle the issue with a quantitative approach. The flexible methodology [42] applied aims at linking a quantitative

approach with the socio-economic aspect evaluation [40]. This innovative approach introduces new results about the analysis of the water sources' vulnerability in North Horr Sub-County.

The result of this research may be relevant for other researchers, since this methodology applies to different types of scant data contexts and risks, as well as to decision makers in Marsabit County as an evaluation tool for the measures undertaken to face water issues contained in the development plan.

The remaining part of the paper proceeds as follows. Section 2 gives an overview of the study area and specific key information on the context on which the analysis is based, as well as information on the materials used; Section 3, separated for clarity reasons from Section 2, addresses the methodology of the analysis and the specific issues regarding the construction of sub-indicators of exposure, sensitivity and adaptive capacity. In Section 4, the main results are analyzed and discussed. Section 6 presents the conclusion of this research.

#### **2. Materials**

In a scant data context, like in the northern part of Kenya, availability of data is a pivotal issue. The materials here used have two different types of source: public structured data, i.e., climatic data, demographic data, spatial data, and planning strategies and data collected in the framework of projects. In particular, data on water sources are retrieved from the One Health platform, developed by the Italian start-up TriM (at the moment only for internal use) in the framework of the One Health project (http://www.ccm-italia.org/one-health-uomo-animale-ambiente-north-horr-2) and from the international organization Concern Worldwide (https://www.concern.net/) which shared data collected in a joint campaign with governmental institutions. Except for soil-related data, the data collected were post-processed to construct geo-referenced data in the form of a point vector defined at village or water-source level.

In addition, the limiting factors regarding nitrate behavior, mainly due to scant data context, are identified and assessed. Nitrate behavior in soils, indeed, is dependent on soil characteristics of drainage and texture to consider its transport to groundwater. The role of nitrate degradation was intentionally left out. Attenuation factors like denitrification processes and dilution can occur in the aquifer and influence nitrate concentration [43]. However, the kinetic of nitrate reduction is likely a zero-order reaction and estimations are very low (μM/L per year) [44]. For this reason and for a precautionary hypothesis, denitrification processes are not taken into consideration. Dilution processes are already assessed through the sub-indicators of physical drought exposure and catchment area.

#### *2.1. Study Area: Geographic Positioning and Climatic Context*

The area covered by this study (Figure 1) is North Horr Sub-County (Marsabit County) in the northeastern region with a particular focus on the surrounding area of eight main villages.

This region is considered as part of the ASALs since the area is mostly desert and partially covered by a shrub savannah. Local communities are mostly nomadic pastoralists breeding camels, sheep, and goats with traditional extensive livestock practice. This practice relies only on naturally available resources of pastures and water and requires energy-intensive movements of herds. From the onset of the dry season, pastoralists move to the so-called *fora* pastures and can walk distances up to 40 km to reach the watering points.

Rainfalls have a bimodal pattern (two rainy seasons alternated with two dry seasons) and a high variability of rainfall due to cycles of wet periods and droughts, although the variations of these events are not well known [45–47].

For clarity reasons, we will here refer to the example of shallow wells. However, the existence of other shallow water sources is based on similar characteristics. In this region, due to the bimodal rainfall pattern, watercourses have a seasonal pattern and runoff can appear once or twice a year [24]. During the rainy season, the seasonal stream's flow is restored and the wells in the riverbed are completely inundated. During the dry season, the water supply is provided by wells dug exactly in the streambed. However, the water extracted is not withdrawn from subsurface runoff, but from the

porosity of sand substrates or cones of depression trapped between upward dykes formed of clay soil [24,48]. Those water sources are used both for human and livestock consumption and water can be extracted by hand or by means of motor pumps. For watering purposes, herds of livestock descend the riverbank and wait for their turn, also for hours, close to the well. Therefore, fecal matter can be left directly in the riverbed while waiting for watering. When the stream's flow is restored, nitrate contamination occurs through direct invasion of the fecal matter in the well, added to an indirect component of nitrate percolation in the ground. Thereby, settling water is infected when the water level decreases under the ground level. Then, after the onset of the dry season, water withdrawal and evapotranspiration cause water reduction in the well. Therefore, the concentration of nitrates increases. This process recurs at each season change from wet to dry season.

**Figure 1.** Study area framework. The main figure represents the study area focused on the surroundings of the main eight villages (Dukana, El Hadi, Balesa, El Gadhe, North Horr, Gus, Malabot, Kalacha). The study area is comprised in North Horr Sub-County (Marsabit County) in northern Kenya.

#### *2.2. Climatic Data*

Precipitation data are the result of a quantile mapping bias correction applied to the Kenya Meteorological Department precipitation gridded dataset [49]. Precipitation data cover the study area with high resolution (0.0375 × 0.0375 degrees) for the period 1983–2014 with a decadal temporal resolution.

#### *2.3. Demographic Data*

Population data are derived from the National Census 2019 [50]. However, there may have been underestimation bias due to severe difficulties in taking a census in an area where people are mainly nomadic with very low population density of about 4 persons per square kilometer. The Kenya National Bureau of Statistic itself declared that the enumeration of nomadic pastoralist population is complex and therefore may lead to population underestimation in ASALs.

#### *2.4. Water Sources*

Water sources in the area are mainly represented by boreholes, shallow wells and pans [51], while piped coverage remains limited [52]. Moreover, 66% of sources have contaminated water, which must be treated before drinking [53].

Water resources and allocation data of all kinds are theoretically available for purchase from Kenya governmental agencies, but in reality these data are often difficult or impossible to obtain [54].

Therefore, water source data, the categories of shallow wells, earth pans and rock catchments are retrieved by the One Health platform and through the Concern Worldwide survey. The Second County Integrated Development Plan for Marsabit establishes the presence of 220 shallow wells, 50 pans and 10 rock catchments in the whole North Horr Sub-County. Through the One Health platform and through Concern Worldwide survey, 54 shallow wells, 6 earth pans/dams and 2 rock catchments are identified and analyzed for nitrate contamination vulnerability in the study area (Table 1). Even if shallow wells are the target for the analysis of nitrate contamination vulnerability, earth pans/dams and rock catchments are also taken into consideration as they are subjected to the same conditions of openness, lack of area protection and confinement.

**Table 1.** Water Source Data in the Study Area.

#### *2.5. Hydraulic Conductivity*

The factors that influence the transport and accumulation of nitrate from the land surface to ground water include sediments, rock type and landscape characteristics [43]. However, land characteristics (land use and slope) are here considered negligible factors. The transport capacity of an aquifer is introduced and defined by the fundamental property of hydraulic conductivity (HC) [55]. In fact, the greater the hydraulic conductivity related to the permeability and porosity of the soil, the higher the resulting nitrate infiltration to shallow underground reservoir. The variables taken into consideration are:

#### *2.6. Civil and Hydraulic Structures*

The proposed analysis investigates the vulnerability at water-source level. In order to understand future changes in water source density, attention is drawn to the actions contained in the Marsabit Second County Integrated Development Plan 2018–2022 (SCIDP) [53]. Among the measures that will be undertaken, only new water sources or rehabilitation of existing water sources contained in the SCIDP are taken into consideration.

#### **3. Methods**

This study on spatial vulnerability assessment for nitrate contamination of shallow wells in riverbed is based on the identification of the IPCC approach [40,41]. In particular, the concept of vulnerability refers to "the propensity of exposed elements such as human beings, their livelihoods, and assets to suffer adverse effects when impacted by hazard events" and can be seen as a situation-specific determinant of risk [41].

Therefore, considering the context and the hazard, the model used is [42]:

$$V = \frac{\text{ExS}}{\text{AC}}\tag{1}$$

Both the Exposure (*E*) and the Sensitivity (*S*) represent the negative effects of the changing conditions, while the indicator of Adaptive Capacity (*AC*) is the parameter which may counteract the negative effect of the impact and therefore improves the vulnerability.

Figure 2 presents an overview of the vulnerability assessment model describing the sub-indicators taken into consideration for the construction of this quantitative vulnerability analysis. As previously mentioned, nitrate contamination of open shallow water sources is a climate-driven issue since the wet periods activate contamination pathways and dry periods reduce the contaminant-to-solution ratio (1). The maximum number of settlements, potentially using the water source, is introduces as a two-way sub-indicator considering the exposure of these settlements and the pressure they bring on water sources (2). Moreover, as highlighted by the literature on the topic, nitrate contamination can occur through direct or indirect pathways (3), therefore sub-indicators of lateral and vertical hydraulic conductivity are taken into consideration. The location of the open shallow water sources (inside, outside or near the stream) (4) is introduced as a sensitivity factor while the adaptation strategies are evaluated through the water sources density (5).

**Figure 2.** Vulnerability assessment model. The reference numbers in the red boxes are used in the text to refer to nitrate contamination dynamics in association with the related sub-indicators.

Technical details on the sub-indicators of Exposure, Sensitivity and Adaptive Capacity are provided in Table 2.

**Table 2.** Indicators and Sub-Indicators of the Vulnerability to Nitrate Contamination.

The indicators of Exposure, Sensitivity, Adaptive Capacity and Vulnerability are represented with a pixel-based visualization with a resolution of 230 m (based on the highest resolution represented by the Drainage and Texture sub-indicators' raster resolution), depending on the location of water points, with the aim of providing a local scale vulnerability analysis.

#### *3.1. Exposure*

3.1.1. Physical Exposure: Standardized Precipitation Index (SPI) for Drought and Flood Assessment

The *SPI* [57] is recommended as the main meteorological drought index from the World Meteorological Organization (WMO) [58]. The *SPI* is used to measure the degree of drought and flood stress through a quantitative description method [42,59,60]. The contamination process, indeed, is influenced both by wet and dry periods. The nitrates contained in fecal matter deposited by livestock contaminate the water through direct and indirect pathways that activate in the wet season. The degree of intensity of the dry period influences the water level in the water source, thus, the contaminants-to-solution ratio. Using the SPI, it is possible to detect the susceptibility of the area to wet and dry conditions.

The single parameter required for its calculation is the precipitation (Equation (2)) and it is generally used as an effective and simple tool for drought assessment. The *SPI* index can be calculated for different time scales (from 1 to 24 months) in order to assess different drought types and wetness conditions [61,62]. Short time scales (1 to 3 months) are mainly related to soil water content and river discharge in headwater areas; medium time scales (3 to 12 months) are related to reservoir storages and discharge in the medium course of the rivers; long time scales (12 to 24 months) are related to variations in groundwater storage.

$$SPI = \frac{P - P^\*}{\sigma\_p} \tag{2}$$

where *P* is the monthly precipitation (in mm), *P*∗ is mean monthly precipitation (in mm) and σ*p* is the standard deviation of precipitation.

The *SPI* index was calculated at village level and for the three existing stations present in a 250 km radius (Lodwar, Marsabit and Moyale town) using the *SPI* program (available online at www.drought.unl.edu/droughtmonitoring/SPI/SPIProgram.aspx). The *SPI* index is calculated using the BCKMD dataset, a bias-corrected satellite-derived precipitation dataset based on the KMD dataset (issued by the official national meteorological service dataset, available at http://kmddl.meteo.go.ke: 8081/SOURCES/.KMD/) corrected with the GPCC [49].

The *SPI* index was computed for different time scales depending on the target. For drought detection the 3-month, 6-month and 12-month time scales were computed, while for flood detection the 1-month and 3-month time scales were detected. Specific weight and ranking values were calculated for drought or flood severity and drought or flood frequencies following the method proposed by [63] for drought risk assessment and already applied in risk assessment studies [42]. Using this methodology, the value of the weighted *SPI* can range from a minimum of 0 to a maximum value of 24.

A known limit of the proposed approach is the presence of many zero rainfall accumulations due to the arid climate. However, if there are many historical zero rainfall accumulations, the estimated gamma distribution may not adequately fit the frequency distribution of the historical rainfall. Therefore, in arid regions, the *SPI* indicator should be interpreted with care [64]. Despite this, the use of monthly cumulative precipitation in this research significantly reduces the number of zero rainfall accumulations and the analysis of *SPI* is reliable.

#### 3.1.2. Demographic Exposure

Nitrate contamination affects human and animal populations. However, statistics on animal population are only partially or not at all available. For this reason, since the local population is mainly part-devoted to pastoralism, we can estimate a proportion between human and animal population and we could assume that the greater the human population is, the greater the number of animals would be. However, due to the low population density of the area, the number of settlements was used instead. To understand the sensitivity of the water sources, the demographic exposure was quantified as the potential maximum number of settlements relying on a single water source. In this area, the pastoralists can walk up to 40 km to water their animals. The people in each settlement in a radius of maximum 40 km can potentially reach the water source. However, they would prefer the nearest sources and then gradually move to farther sources. Therefore, the counting of settlements relying on the water source (*Nsettlements*) is weighted using the inverse of the distance between each settlement and the water source (*dx*).

$$N\_{settlemnts=-} = \sum\_{\mathbf{x}=1}^{n} \frac{1}{d\_{\mathbf{x}}} \tag{3}$$

Thus, settlements that are closer to the water source have higher weights, while the farther ones have lower weights. The values of the weighted maximum number of settlements potentially using the water source range from 1.2 (minimum value) to 480 (maximum value).

#### *3.2. Sensitivity*

#### 3.2.1. Presence of the Stream

The presence of the stream constitutes a sensitivity sub-indicator due to the already explained contamination dynamics. In fact, the water points situated in the riverbed are highly sensitive, the water points near the stream are moderately sensitive, the water points and springs far from the riverbed show a low sensitivity (classified as "outside"). The inside/near/outside classification of the different water sources is made through the direct comparison of satellite images and the geo-referenced water sources since this operation would not have been possible with automatic processes. The sensitivity is then expressed through quantitative weights (adapted from [65]) (Table 3).

**Table 3.** Weights Assigned for the Presence of the Stream.

#### 3.2.2. Hydraulic Conductivity

Soil texture and soil drainage classes were reclassified according to coefficients of vertical [66] and lateral [67] hydraulic conductivity respectively (Tables 4 and 5). The soil texture sub-indicator was then averaged across the seven layers to obtain a single vertical HC layer.

**Table 4.** Texture Classes Classifies According to the Coefficients of Vertical Hydraulic Conductivity.

**Table 5.** Drainage Classes Classified According to the Coefficients of Lateral Hydraulic Conductivity.

#### *3.3. Adaptive Capacity*

The evaluation of the adaptation strategies focused on adaptation actions rather than the development or improvement of the institutional framework since they are long-period approaches or other strategies like risk-transfer methods since they are not problem-solving oriented. Other strategies to avoid vulnerability issue like local and conventional actions were discarded. In fact, local strategies in the ASALs against water scarcity mostly rely on traditional adaptation mechanisms, above all, the adoption of nomadic life or increase of watering distance as closer waterpoints are depleted [68]. Conventional adaptation strategies, such as restriction of water use in pans and boreholes during rainy season until surface runoff has been exhausted, controlling the number of livestock that access the pans and boreholes, and paying infrastructure maintenance fees to help increasing water availability for longer periods, are sparsely adopted. However, a more sedentary life and demographic increase are threatening water availability in inhabited areas [69]. For these reasons, the limits of local adaptation capacity must be overcome through the adaptive actions set in place by local governmental institutions. Based on the SCIDP [53], there are eight actions that contribute to the improvement of water sources: installation of gensets and solar panels, construction of shallow wells, supply of fresh and clean piped water, drilling of boreholes, installation of water towers, construction of a dam, installation of underground tanks piped water filled, water trough (Table 6).

**Table 6.** Adaptation Actions (Installation of Gensets and Solar Panels, Construction of Shallow Wells, Supply of Fresh and Clean Piped Water, Drilling of Boreholes, Installation of Water Towers, Construction of a Dams, Installation of Underground Tanks Piped Water Filled, Water Trough) Divided According to the Intervention Areas.

Compared to the current adaptation scenario (AC0), the implementation of the actions stated in the SCIDP will move to a future adaptation scenario (AC1). Therefore, two adaptation scenarios were constructed (AC0 and AC1) where the water sources density in the project area is used as proxy of the sub-indicator of the walking distance to water sources as suggested by [70]. The AC0 scenario, thus, represents water source density ante-SCIDP and the AC1 scenario represents water source density (i.e., ante-SCIDP water sources plus new water sources planned) post-SCIDP.

#### *3.4. Vulnerability*

The vulnerability is the summary indicator obtained from the combination, based on Equation (1), of the previously analyzed indicators and sub-indicators. Each indicator (Exposure, Sensitivity and Adaptive Capacity) was rasterized (WGS 84/UTM zone 37 N, 230 m × 230 m) and normalized in the range 0–10 to be comparable. Then, Exposure and Sensitivity were multiplied together obtaining the potential impacts and finally divided by the Adaptive Capacity counteracting the negative effects of the impacts. As per the scale interpretation, high values correspond to high values of each indicator and of vulnerability.

#### **4. Results**

#### *4.1. Exposure*

#### 4.1.1. Demographic Exposure

The water sources in the surroundings of Dukana show a higher weighted number of settlements and therefore these are the most exposed areas in North Horr Sub-County (see Figure 3a). Some water sources in the western part of the sub-county have a medium demographic pressure. The rest of the water sources are less stressed.

#### 4.1.2. Weighted SPI Index

Although there is a suitable timescale for each specific context, it may be helpful to present results for alternative timescales [71] to observe the variability of the index. SPI index weighted for each main village and station shows different performance according to the time scale (Table 7).

**Table 7.** SPI Index at 3-, 6- and 12-Month Timescales for All the Facilities.

The following considerations on the choice of the timescale for detecting flood and drought spells are since, at this latitude, rainfalls are concentrated into two seasons of three months each. Rain events that trigger fecal matter intrusion in shallow water are extreme events. The 1-month SPI can assess deviation from normal monthly cumulated precipitation better than the 3-month SPI, which can better assess seasonal deviations. Therefore, the 1-month SPI was used as a sub-indicator for physical flood exposure, as it can detect areal susceptibility to wetness conditions (see Figure 3b). The 6-months SPI was preferred to the 3- and 12-month timescale as it can detect two consecutive dry seasons and potentially the onset of a drought period. Therefore, we used it as the sub-indicator for physical drought exposure as it can be very effective in showing reduced streamflow and reservoir levels (see Figure 3c).

#### *4.2. Sensitivity*

#### 4.2.1. Presence of the Stream

The greatest number of water sources that are situated exactly in the riverbed is found in the North and in the East of the sub-county. Therefore, this is where it is possible to find the open water sources that are more sensitive to nitrate contamination (see Figure 4a).

**Figure 4.** Sensitivity sub-indicators: (**a**) presence of the stream, (**b**) soil texture, and (**c**) soil drainage.

#### 4.2.2. Hydraulic Conductivity

The two sub-indicators of hydraulic conductivity (vertical and lateral hydraulic conductivity) describe the permeability to contaminants in the area. In the lowlands in the central-southern part of the North Horr Sub-County there are the greatest rate of vertical hydraulic conductivity due to the presence of the northern part of the Chalbi desert. In the northern part of the sub-county, the vertical hydraulic conductivity decreases with the increase of the altitude (see Figure 4b).

Regarding the lateral hydraulic conductivity, higher values of drainage are found along the watercourses and in the highlands at the starting points of the watersheds (see Figure 4c).

#### *4.3. Adaptive Capacity*

Among the eight actions that contribute to the improvement of water sources, only four contribute significantly to the reduction of the walking distance to safe water sources. These are construction of shallow wells, supply of fresh and clean piped water, drilling of boreholes, installation of underground tanks filled with piped water. Therefore only the following water sources were taken into consideration for the water sources density (Table 8).

**Table 8.** Number and Distribution According to the Type of Water Sources Taken into Consideration for the Water Sources Density in AC0 and AC1.

The increase of the number of safe water sources in the study areas is considered as an improvement of the adaptation capacity. It lowers the animal gatherings at water sources, it reduces the exploitation of water sources themselves and improves access to water.

The scenario AC0, as said, is the current state of density of water sources, while the scenario AC1 is the possible future scenario if all the planned measures are set in place by the end of 2022. In both scenarios, North Horr and El Hadi are the inhabited centers with the higher concentration of water sources.

#### *4.4. Vulnerability*

The vulnerability is the resulting combination of normalised indicators: Normalised Exposure (see Figure 5), Normalised Sensitivity (see Figure 6) combined with the Scenarios AC0 and AC1 (see Figure 7) after their normalization in Normalised AC0 (Figure 8a) and Normalised AC1 (Figure 8b). The vulnerability analysis has a major outcome: both in Scenario 0 and Scenario 1 (Figure 9) the northern part of the sub-county is more vulnerable compared to the rest of area. After the implementation of adaption measures there is a timid improvement in vulnerability values in the southern sub-county (whitish spots). In Scenario 1 (Figure 9b), where there are no new adaptation measures (northern part), the values of vulnerability show no change.

**Figure 5.** Normalised Exposure.

**Figure 6.** Normalised Sensitivity.

**Figure 7.** Adaptation sub-indicator: (**a**) density of water sources (AC0) and (**b**) density of water sources (AC1).

**Figure 8.** *Cont.*

**Figure 8.** Adaptation indicators: (**a**) Normalised AC0 and (**b**) Normalised AC1.

**Figure 9.** Vulnerability indicators in two adaptation scenarios (density of water sources): (**a**) Scenario 0 with the current state of adaptation (**b**) Scenario 1 with implementation of the measures contained in the SCIDP.

#### **5. Discussion**

The result showed that the values of vulnerability in Scenarios 0 and 1 are greater in the northern part of the sub-county (dark red areas) with respect to the southern part (white to light red areas). Very few changes occurred from Scenario 0 to Scenario 1.

In fact, compared to Scenario 0, with the implementation of the adaptation measures—concentrated in the southern and central part of the sub-county—only the areas surrounding Gus, Malabot, North Horr, Kalacha, El Gadhe, Balesa and El-Hadi reduces their vulnerability. The area in the North do not benefit from the adaptation actions. Indeed, the areas in the North that were more vulnerable in Scenario 0 remain the most affected also in Scenario 1, while the areas in the South improve their capacity to adapt to nitrate contamination risk.

The measures contained in the SCIDP that aim to improve water access are concentrated in the southern-central part of the sub-county around the main town of North Horr (Figure 10a). Indeed, it seems possible to observe a radial pattern distribution of the areas of intervention starting from North Horr. As a matter of fact, North Horr is the chief town of the sub-county. Although it is difficult to reach North Horr from Marsabit town passing through the Chalbi desert, the areas in the North are way more difficult to get to and very close to the border with Ethiopia. The organization of similar interventions in the northern area could be challenging from a logistic point of view. Therefore, North Horr seems to be prioritized in the decision-making process. Moreover, the availability of funds is hardly employed in remote areas where the population density is one of the lowest in all of Kenya (about four inhabitants per km2) [50]. In fact, at the moment, funds of sustainable growth are preferably diverted in the areas along the Great North Road (the road going from El Cairo to Cape Town passing through Marsabit County), where a rapid population influx is expected [53].

**Figure 10.** (**a**) Scenario 0 and the planned areas of intervention; (**b**) Scenario 1 and the demographic exposure.

Besides the low population density in the northern part of the sub-county, the demographic pressure on few water sources is an issue. In fact, a great number of settlements rely on few water sources creating significant stress for water supply dynamics (Figure 10b).

Therefore, remoteness of the northern part of the sub-county, security problems, scarce interest, and high demographic pressure on the scarce number of water source create suitable conditions for water scarcity and low water quality. Despite the SCIDP's intention to promote the development of the area for the period 2018–2022, the plan will not be able to rectify the asymmetries and enhance the easiest access to quality water. If not addressed soon, the associated consequences could be an increase in migration sometimes identified as urbanization processes and conflict escalation in the area over water resources. Moreover, worsening consequences could be deteriorated by climate changes and, in particular, by more hydro-climatic variability in space and time [72].

To prevent social inequalities in access to clean and safe water, a broader understanding of the existing water quality in Kenya is necessary. However, poor knowledge and application of the Groundwater Vulnerability Assessment are found [73], even if contamination are common problems that affect groundwater quality [74].

These results and the related discussion confirm that the adopted methodology solves the issue of vulnerability assessment in a scant data context. In fact, the methodology proposed can identify the most vulnerable areas of the sub-county, together with most vulnerable shallow water sources, considering a selection of specific available data. Thus, the scant data limit is overcome and addressed. A limitation could be a lack of groundwater NO3 concentration data; however, an in-situ extensive data collection campaign would be a major effort for the abovementioned logistics issues. Thanks to the methodology proposed, more vulnerable areas are identified and a more narrow group of water sources to be analyzed could be selected, as done by [75]. Alternative applications of this methodology could be useful to assess the vulnerability in other scant data contexts as support for decision making or as preliminary assessment for more in-depth analysis of the water sources regarding nitrate contamination processes.

#### **6. Conclusions**

This research aimed at assessing the vulnerability of the area to nitrate contamination of water in open shallow water sources due to fecal intrusion following flooding events and nitrate percolation in groundwater. The vulnerability indicator was constructed according to two different scenarios pre- and post-interventions contained in the SCIDP, respectively Scenario 0 and Scenario 1. The result obtained shows the partial inefficacity of the interventions since they are concentrated in the central part of the sub-county, where it is already possible to find most of the water sources of the area. The northern part of the sub-county is remote, insecure, and scarcely populated, therefore, there is limited ability and low interest in improving water access in these areas.

Since the adaptation measures planned do not intervene in the most vulnerable areas, at least until 2022, the reduction of nitrate levels in the water supplied may rely on different control methods based on the acceptable level of human health risk, nitrate-control cost and technical feasibility. These methods include nitrate source control, blending of two or more water supplies and direct treatment of nitrates [76]. These methods of nitrates control should be coupled with an awareness campaign on nitrate contamination control.

Moreover, the consistency of the results confirms the goodness of the proposed methodology for scant data context based on the selection of specific quantitative sub-indicators, combining socio-economic aspects with physical features.

In conclusion, the present study contributed to the understanding of the present and near-future vulnerability of the area, as well as of the limitations of the SCIDP in contrasting the risk of nitrate contamination of shallow water sources. Policymakers should be aware of the existing imbalances between the North and South of the sub-county and try to incorporate these findings, albeit achieved in a scant data context, for future policy planning. At the same time, it is demonstrated that a quantitative approach can be easily used to evaluate the vulnerability to climate changes also in a scant data situation and in remote areas.

**Author Contributions:** Conceptualization, V.B. and. A.P.; methodology, V.B., A.P., E.C. and M.R.; formal analysis, V.B.; writing—original draft preparation, V.B.; writing—review and editing A.P., V.B., E.C. and M.R.; supervision, A.P., E.C. and M.R. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This study is conducted in the framework of the International Cooperation Project "ONE HEALTH: Multidisciplinary approach to promote the health and resilience of shepherds' communities in North Kenya" funded by the Italian Agency for Development Cooperation (AICS). The authors would like to thank the project coordinator (CCM) and project partners (TriM and VSF-Germany) and the Kenyan Meteorological Department. Finally, a due thank to Concern Worldwide which shared data on water sources collected in a joint campaign with the Government of Kenya.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

### *Article* **Mitigation of the Water Crisis in Sub-Saharan Africa: Construction of Delocalized Water Collection and Retention Systems**

**Adolfo F. L. Baratta 1,\*, Laura Calcagnini 1 , Abdoulaye Deyoko 2, Fabrizio Finucci 1 , Antonio Magarò 3 and Massimo Mariani 3**

**Abstract:** This paper presents the results of a three-year research project aimed at addressing the issue of water shortage and retention/collection in drought-affected rural areas of Sub-Saharan Africa. The project consisted in the design, construction, and the upgrade of existing *barrages* near Kita, the regional capital of Kayes in Mali. The effort was led by the Department of Architecture of Roma Tre University in partnership with the Onlus Gente d'Africa (who handled the on-the-ground logistics), the Department of Architecture of the University of Florence and the École Supérieure d'Ingénierie, d'Architecture et d'Urbanisme of Bamako, Mali. The practical realization of the project was made possible by Romagna Acque Società delle Fonti Ltd., a water utility supplying drinking water in the Emilia-Romagna region (Italy) that provided the financing as well as the operational contribution of AES Architettura Emergenza Sviluppo, a nonprofit association operating in the depressed areas of the world. The completion of the research project resulted in the replenishment of reservoirs and renewed presence of water in the subsoil of the surrounding areas. Several economic activities such as fishing and rice cultivation have spawned from the availability of water. The monitoring of these results is still ongoing; however, it is already possible to assess some critical issues highlighted, especially with the progress of the COVID-19 pandemic in the research areas.

**Keywords:** water crisis in Africa; water collection and retention systems; sand dam; migration; climate change

#### **1. Introduction**

Mali is a landlocked country located in West Africa and 51% of its land is occupied by desert. The cultivated area is 4.7 million hectares, approximately 4% of the entire territory [1]. The country is characterized by the following major types of land:

**Citation:** Baratta, A.F.L.; Calcagnini, L.; Deyoko, A.; Finucci, F.; Magarò, A.; Mariani, M. Mitigation of the Water Crisis in Sub-Saharan Africa: Construction of Delocalized Water Collection and Retention Systems. *Sustainability* **2021**, *13*, 1673. https://doi.org/10.3390/su13041673

Academic Editors: Maurizio Tiepolo, Vieri Tarchiani and Alessandro Pezzoli Received: 28 December 2020 Accepted: 31 January 2021 Published: 4 February 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

About 47% of the Malian territory is made up of the Niger basin, while the basin of the smaller watercourse called the Senegal River covers 11% of the territory. The Volta basin, the third largest river, corresponds to 1% of the country's surface area, while the remaining 41% is covered by the Sahara Desert. Of note, 1700 km of the 4200 km of the Niger River run through Mali. The Niger and Senegal rivers, and the intricate network of tributaries, provide most of the permanent sources of surface waters. The total average surface water volume is estimated at around 50 km3/year. Niger alone contributes 35 km3/year, a third of which is wasted by evaporation. Renewable water resources, present in the subsoil, can be estimated at around 20 km3/year, half of which is water in common between surface and subsoil. Therefore, in the whole country, the total volume of renewable water is equal to 60 km3/year. The surface water resources entering the country amount to 40 km3/year, mostly from New Guinea (33 km3/year) and from the Ivory Coast (7 km3/year) [5]. For the exploitation of these water resources, the country counts on the presence of five dams (Table 1), for a total water capacity of 13.8 km3 (Figure 1) [6].

**Figure 1.** Water flows of the Niger River system and dams' position (Source: Authors').

Only 5% of renewable water resources available to Mali are exploited. Almost all of the water comes from seasonal surface sources, available only in the period from June to December. Only the withdrawals for the communities come from underground water resources, except for the city of Bamako, whose water is drawn from the Niger River [7]. The reasons why groundwater resources are so poorly exploited can be found in:

Furthermore, the complexity of the country's resource management organization hinders the implementation of any water policy (Table 2).

**Table 2.** Organization chart of the Ministries, Departments and Offices that deal directly or indirectly with water resource management [6].

In addition, a new agency was created in 2002. The *Agence du Bassin du Fleuve Niger* (ABFN) (Niger River Basin Agency) was mandated with safeguarding the Niger basin, as well as the management and integration of water resources in coordination with the corresponding cross-border agencies. The intricate context of governing bodies has given rise to an equally complex regulatory framework through which the management of water resources enjoys little optimization. Ultimately, Mali is characterized by the presence of important water resources, but these are ill distributed over the territory and their strong seasonality is poorly managed.

The access rate to drinking water in Mali is 61% in rural areas and 69.2% in urbanized areas [8]. Bad distribution is followed by bad management, made up of a plethora of bodies with overlapping competencies, scarce powers and a complex regulatory system detached from the local realities (Table 3).

Besides its health implications, access to clean water is considered a human right and is a prerequisite for the realization of other human rights [9]. Therefore, the United Nations, with resolution 64/292 [10], has asked countries and international organizations "to provide financial resources, help capacity-building and technology transfer to help developing countries to provide safe, clean, accessible and affordable drinking water and sanitation for all".

#### **Table 3.** Main regulations on water management in Mali [1].

The paper focuses on the research, design, and implementation process aimed at the construction and upgrade of existing *barrages* in rural areas of Sub-Saharan Africa.

#### *Water Crisis, Climate Change, Internal Conflict, and Migration*

Climate change is among the factors with the greatest impact on the water crisis throughout Sub-Saharan Africa. It will affect those countries, such as Mali, that heavily depend on more less diversified and strongly seasonal agriculture [11].

The climatic conditions of the country (Figure 2) are characterized by average temperatures between 27 and 30 ◦C annually, with large temperature variations occurring mainly in the desertic areas of the north [12]. In 2015, the maximum recorded temperature was 51 ◦C and the minimum was 10 ◦C [13]. The rainy season varies according to latitude: in the south of the country, it lasts up to 6 months, with a marked increase in rainfall between June and October, while in the north it is reduced to just three months between July and September.

The rainfall in the areas close to Sahara is only 50 mm/year, in the Sahel area it is between 100 and 1100 mm/year, while in southern Mali it exceeds 1100 mm/year [12]. Furthermore, Mali is in the so-called Intertropical Convergence Zone where the typical monsoons of West Africa occur. Due to climate change, between 1960 and 2015, the average temperatures increased by 1.2 ◦C, with a future expectation of linear growth: it is estimated that, by 2050, temperatures could increase between 0.9 and 1.5 ◦C, with the largest increase in the Kayes region. These changes could have an impact on the amount

and patterns of rainfall, the main source of hydrological supply. The rain cycle in Mali is decades-long and has undergone a decrease of 4.4 mm/year from 1950 to 1983 and an increase of only 2.6 mm/year between 1983 and 2015 (Figure 3). Mathematical models predict a slight average increase in precipitation (between 1% and 3%) together with a major decrease in the northern driest regions. Furthermore, the variation in the seasonal distribution could shift the wettest period towards the early part, between June and July with a subsequent reduction (between 6% and 10%) for the rest of the period (Figure 3). In addition, rain-related destructive phenomena are expected to increase [14].

**Figure 2.** Mali bioclimatic zones and geographic classification of Kayes region (Source: Authors').

The impact on water resources could be substantial: there would be a reduction in the rate of subsoil resources and, at the same time, an increase in their need because the surface resources would tend to be less available due to intrinsic phenomena (such as the increase in evaporation because of the increase in temperature) and extrinsic (such as the growth in demand for water as a consequence of population growth) [15]. The result of climate change could be a decrease in food security (already under acceptable levels in the regions of Gao, Segou, Tomboctou, and Mopti) and malnutrition (acute childhood malnutrition already affects 13% of children under 5), resulting in increased mortality and reduced life expectancy [16].

The difficult political situation linked to internal conflict, which in June 2019 caused the forced migration of almost 148,000 Malians [17], could exacerbate this perspective. Political instability in Mali has its roots in the period following independence from France, obtained in 1960. The first independent government pursued real-socialism policies and nationalized all the industries in the country except for cotton. In the following five years, the country's economy nearly collapsed and Mali was forced to ask for financial support for currency to its former colonizer. A series of periods of crisis followed, leading to five coup attempts between 1970 and 1990. From the early nineties onwards, multiparty democracy began to consolidate, not without violence. Since 1990, the situation has become complicated

due to the revolts of the Tuareg people, who have settled in the north of the country. They gave life to the revolutionary movement *Mouvement Populaire de l'Azaouad* (MPA) with the aim of "liberating" the territory to the north by force [18]. The conflict officially ended in 1995 and re-exploded in 2007 due to the dissatisfaction of the Tuareg soldiers integrated into the Malian army. In 2012, the MPA was transformed into the National Movement for Liberation of Azawad (MNLA) [19], which found support in Islamic terrorist groups (Al Qaeda and Ansar). Moreover, Libya, until the fall of Gaddafi, supplied arms to the Tuareg that were superior to those available to the Malian army [20]. The declaration of independence of northern Mali, by the MNLA, saw the emergence of conflicting views between the Tuareg and Ansar. The MNLA and the Jihadist group clashed and brought the Tuareg closer to the national government [21]. However, in 2015 the Tuareg accused the Malian government of not respecting the agreements and the terrorist attacks began again.

**Figure 3.** Anomaly of total precipitation [m] compared with anomaly of 2 m temperature (◦C), historical series, in Sahel (12◦ N–17◦ N, 18◦ W–42◦ E). (Data source: Climate Change Institute, University of Maine, 2020).

Climate change, food insecurity, and social, economic, and political instability cause migration. Migration flows abroad come mainly from rural areas (73%), are characterized by a male majority (66%) and have as their primary destination the Ivory Coast (70%). As for long-distance destinations, due to the tightening of entry conditions in some European countries of traditional destinations such as France, the choices of Malian migrants fall on southern European countries such as Spain and Italy.

Rationalizing and improving the management of water resources, especially at the local level, would promote food safety, with the consequent reduction in mortality. In addition, improving the country's agropastoral economy would mean reducing political instability, and, over time, popular revolts. Therefore, a stable water supply would improve the living conditions in the country and reduce migratory phenomena.

#### **2. Materials and Methods**

This three-year research project (2017–2020) started with the cultural and scientific cooperation agreement between the nonprofit organization *Gente d'Africa* and the Department of Architecture of Roma Tre University (P.I., Prof. Adolfo F. L. Baratta, Research unit coordinator Prof. Fabrizio Finucci), with the aim of providing guidelines for the self-construction of infrastructure dedicated to health, food, and water in the depressed areas of Sub-Saharan Africa. Since 2015, the research group of Roma Tre University has been involved with addressing housing, social, and health problems in marginal areas of the world. With the aim of intervening specifically to address the water crisis in Mali, the two partners obtained the operational collaboration of the University of Florence and *Architettura Emergenza Sviluppo* (AES), a nonprofit organization founded in 2016. *Romagna Acque Società delle Fonti* Ltd. provided most of the financing. Furthermore, since 2019, an international cooperation program has been in place between the Department of Architecture of the University of Roma Tre and the *Ecole Superieure d'Ingénierie d'Architecture et d'Urbanisme* (ESIAU) of Bamako (P.I.: Prof. Abdoulaye Deyoko). ESIAU represents the only point of reference for architecture teaching in the entire country. This collaboration produces the planning, design, and construction of small and medium-sized infrastructures, with prevalent hydraulic characteristics in urban and rural areas. These water infrastructures include the distribution network, terminals, and water capture systems aimed at creating artificial basins, the so-called *barrages*. The *barrages* are barriers with a dam function, equipped with locks for the control of flooding.

The project was carried out in the following phases:

The Italian and Malian universities have focused on the opening of the Erasmus Program beyond the European borders, implemented by the European Commission through the Key Action 107, International Credit Mobility, responding to the Call 2019 and being recently (August 2020) awarded the funding for carrying out the activities of cultural cooperation and international educational exchange.

Although the French term *barrages* is mainly used to indicate medium and large dams, in the context of rural settlements it is used to allude to small structures, able to stop or channel the waters coming from the swelling of the streams during the rainy season. In Africa, such structures, also known as sand dams, help the replenishment of the aquifers [22]. *Barrages* are containment structures that can be classified according to the ability to convey subsoil water or surface water into two types (Figure 4):

**Figure 4.** Concept diagram of *barrage* (sand dam): (**a**) Underground *barrages*. (**b**) Surface *barrage* (Source: Authors').

The underground *barrages* are made by digging a deep excavation down to a rocky layer or sufficiently compact soil, allowing for an ordinary foundation of limited size and preventing water from penetrating to greater depths, determining the depth of the aquifer.

The surface *barrages* follow the same principle; however, they are set on a shallow foundation and are designed to stop the watercourse when it swells on the surface because of abundant rainfall on geologically impermeable and compact clay soils.

The *barrage* structure works in a simple but effective way with minimum environmental impact. Because of its small size, it allows overtops water to flow over the *barrage* and avoids draining the aquifer downstream, slowing down the flow of water and facilitating the filling of wells [23].

The surface *barrages* generate an artificial basin which, fed during the rainy season, forms a water reservoir ahead of the dry season. Both *barrage* types, when locally built, use simple construction techniques and intuitive technical principles based on locally available materials. As a result, most of the existing surface *barrages* in Mali are weak structures, often without any foundation. They are incapable of resisting the water pressure as they exploit their weight and shape instead of the characteristics of the material. The poor culture of maintenance means that they are destined to become partially buried due to the accumulation of debris on the upstream-facing side. Furthermore, the lack of a system of local know-how transfer prevents the diffusion of the construction techniques, especially when not based on traditional methods like the use of raw earth, and the correct propagation of a "rule of the art" that could consolidate over the time and could spur any innovations.

However, in many cases the surface and underground *barrages* have been combined in a single structure capable of slowing down the surface flow and increasing the infiltration of water into the subsoil, ensuring greater availability of water resources.

#### **3. Results**

One of the main results of this project was the reconstruction and monitoring of two *barrages*, respectively near the village of Toumbouba and the village of Kofeba, close to Kita, one of the most important towns of the Kayes region, 200 km from Bamako. Both are surface *barrages* although they are different in size and required a completely different approach.

#### *3.1. The Barrage in Toumbouba*

Located at the geographical coordinates 13◦01- 07.58-- North Latitude and 9◦21- 01.04-- West Longitude, the Toumbouba *barrage* (locally known as Tumumba) is grafted onto a preexisting structure built a few decades ago. The original *barrage* was a stone masonry structure, 60 m long, grafted to the north in a retaining wall of an embankment, orthogonal to the position of the main structure. The containing wall resisted the horizontal thrust

due to its shape, having a triangular section with the hypotenuse inclined by about 45◦. The structure was built on ordinary foundation made by an excavation of a few tens of centimeters below the ground level, filled with large aggregate material bound using cement. The elevation structure had a larger size than the foundation, laying at least two thirds directly on the riverbed. The historical memory of the village traces its construction back to the mid-eighties, but the oral tradition did not confirm any certain source.

During the first on-site survey, in April 2017, it was determined that the power of the watercourse in 2007 caused the overturning of the structure and its breaking into three sections. The first section remained firmly buried for its entire length, while the most stressed section, about 15 m long, divided into two parts, laying down on the bed of the watercourse showing the weakness of the construction technique. The torsion due to the overturning caused damage in need of repair to the orthogonal retaining wall, and the erosion of the water caused the dissolution of a large part of the embankment it contained, jeopardizing the necessary shape of the reservoir. During the survey, the research team acquired the preliminary knowledge of the availability of materials and the skills of the local workforce. It learned of the almost absent theoretical and practical knowledge of the use of steel for construction of flexible structures, and, on the other hand, of the recent use of concrete blocks. These could be easily made in large quantities with handmade block molds as demonstrated in the large urbanizations of Bamako and Kita, where they have replaced the use of the traditional Malian raw earth adobe techniques. The survey ended with the inspection of the damaged structure, to proceed with the design phase. The mold for the construction of the concrete blocks for the vertical elevation was designed first, while the two overturned sections were demolished, and the rubble removed. Those operations were carried out with the help of nearby villagers. The design of an armed and buttressed structure was prepared next, one able to offer the greatest resistance to horizontal thrust, combining shape and flexibility. The construction costs were summarized in a bill of quantities, using the prices recorded in the initial inspection phase as a reference and cross-checking them with the international price list integrated in the CYPE software package [24]. The second mission, aimed at the construction, was organized into two phases. During the first phase, in February 2018, the base of the *barrage* was built. While waiting for the setting and curing of the concrete, the concrete blocks were manufactured. During the second phase, in April 2018, the *barrage* was built (Figure 5), and the gaps in the retaining wall of the embankment and on the embankment itself filled.

The result is a wall structure with variable thickness, strongly reinforced in both directions, buttressed, 15 m long and 2 m high, connected to the preexisting structure through the insertion of steel bars Φ16 and concrete injections every 40 cm in elevation for a depth of at least 60 cm. The structure was finished with a 3 cm thick cement-based plaster, to account for the expected lack of maintenance in the future (Figure 6).

During the survey it was decided to intervene with the consolidation of the structure and the reinforcement of the embankment adjacent to the *barrage*. Furthermore, the correct hydraulic functioning of the structure was tested and proved capable of creating a water reservoir of 6.8 hectares with a depth varying between 30 cm and 2 m, corresponding to a water reservoir of about 45 thousand m3 in the period of maximum capacity. The basin serves, directly or indirectly, a very vast territory comprising about 20 villages, or 40 thousand inhabitants.

#### *3.2. The Barrage in Kofeba*

The work for the Kofeba *barrage* benefited from the experience gained by the group during the work in Toumbouba. The introduction of several practical innovations in the workflow resulted in a shortened construction time without compromising full functionality.

Identified by the geographic coordinates 13◦01- 01.77-- North Latitude and 9◦35- 43.60-- West Longitude, the *barrage* is located near a village which in the maps takes the name of Forongo, locally known as Kofeba, located 15 km west of Kita. Like the *barrage* in Toumbouba, the *barrage* in Kofeba was a preexisting structure in stone laid with cement, 215 m long and 80 cm high, with a particular shape whose triangular section provides an acute angle of just 30◦ near the shutter plane. The regulation of the capacity of the basin was carried out through the manual handling of two rudimentary iron closures, hinged as doors without the presence of a linear counter frame or fixed frame.

**Figure 5.** The rebuilding process in Toumbouba: (**a**) the old *barrage* down; (**b**) the building phase; (**c**) the wall complete; (**d**) the *barrage* working phase (Source: Authors').

Over time, this simple moving mechanism has yielded, bending from the rotation plane of the hinges due to the constant horizontal thrust. Because of both the design weakness of this system and the difficulty in finding suitable metal artifacts, it was decided to fill the openings with a wall. Like for the *barrage* in Toumbouba, some demolition works of part of the structure became necessary, because between the two doors there was a wall fragment about 1 m wide.

The demolition left a gap of about 3 m to be filled with the new wall. Given the small size, steps were taken with the aim of making the construction process more efficient and avoid an additional trip. Following a first mission carried out in December 2019, it was possible to ascertain the presence of a solid foundation structure, as wide as the thickness of the base of the wall, or about 2 m, and about 50 cm deep. Therefore, it was decided to proceed with the drilling of holes for the insertion of steel bars ahead of the reinforcement of the structure in elevation, filling the holes with concrete injections. The new wall was built with two imbedded water outlets to control water overflow.

While the work on the Toumbouba *barrage* was carried out without the aid of machinery or construction equipment, for the Kofeba *barrage* it was necessary to use a hammer drill capable of realizing the appropriate depth holes, powered by an electric power generator. In the lapse of time between the two missions, concrete blocks were built with the same procedure already used in Toumbouba, and the material necessary for construction was set aside.

**Figure 6.** The executive design of the *barrage* in Toumbouba (Source: Authors').

The experience previously gained allowed the completion of the construction phase in only 4 working days (Figure 7). The monitoring phase of the Kofeba *barrage* has just started, since, at the time of writing, the rainy season had just begun, but the first photographic surveys to verify the strength of the structure appear satisfactory. At full capacity, in the absence of further settling of the reservoir grounds and with the help of small additional earthworks, the Kofeba basin could cover an area between 9.5 and 20 hectares.

Although belonging to the same typology, the two *barrages* have very different dimensional characteristics (Table 4).

**Table 4.** Comparison between the main data of the two *barrages*.

The Toumbouba *barrage*, although smaller in size, required considerable effort to restore the reinforced concrete foundation along the entire collapsed section. In addition, the water on the Toumbouba *barrage* reaches a very high speed, generating problems of resistance to dynamic thrust. For this reason, both the foundations and the wall in elevations required a greater mass and a longer construction time.

**Figure 7.** The rebuilding process in Kofeba: (**a**) the old *barrage*; (**b**) the building phase; (**c**) the wall complete; (**d**) the *barrage* working phase (Source: Authors').

> Kofeba's intervention (although it is a larger *barrage*) is more contained in terms of size, moreover, it was possible to use the existing foundation section. The Kofeba basin tends to fill gradually with respect to that of Toumbouba and with a lower height of the water level. These aspects have allowed a smaller wall thickness and, therefore, a much shorter period of work. At the same time, however, the Kofeba area required numerous smaller restoration interventions of the natural embankment, carried out with boulders and concrete by the local labor force.

> Both interventions on the *barrage*, for the number of villages and beneficiaries' inhabitants, are characterized by an excellent cost–benefit ratio.

#### **4. Discussion**

The reconstruction of the two small *barrages* has yielded several benefits that can be classified into two categories: direct benefits and indirect benefits.

Regarding direct benefits, the following can be mentioned:

About indirect benefits, the following should be noted:

Given the quality of the results achieved when compared to the very low costs of both interventions (less than 25 thousand euros), the benefits far exceeded the costs incurred. In particular, the benefits can be classified as:

The monitoring phase of the project is still underway to assess its full environmental and economic benefits. A feasibility study is currently looking at the construction of a control station for the acquisition and monitoring of environmental variables, such as temperature, humidity, and pressure, with the aim of demonstrating the micro-climatic variations due to the presence of the water basin.

Data collection relating to the economic benefits indirectly related to the presence of the water basins is ongoing. Several micro-entrepreneurial activities are being observed, such as commercial fish farming, rice cultivation for the sustenance of the community and for retail sale, the appearance of several vegetable gardens, and the introduction of the seasonal rotation of crops.

In particular, in the fish farm in Toumbouba, an artificial pond of about 150 m3 in capacity was built. This pond was built by excavating; the walls were covered with reinforced concrete, while on the bottom a layer of about 20 cm of compacted earth was created, containing no less than 10% clay, measured by empirical sedimentation tests. This waterproof system, often used for depths not exceeding 3 m, is not recommended for greater depths, where it is advisable to proportionally increase the thickness of the compacted earth. In addition, depths that exceed the height of the aquifer should not be waterproofed in this way to facilitate filtrating of water. The tank requires pumping for the loading and drainage of water, which is periodically necessary for the removal of organic sediments. This periodic maintenance avoids regulating the concentration of oxygen in the water by means of additional mechanical systems. The water of the farm is derived from the *barrage*, by means of mechanical pumping. Therefore, a discontinuous flow was preferred, necessary to replace the evaporated water. To begin breeding, fifty pairs of a

local catfish species weighing between 300 and 400 g were placed in the tank. To facilitate reproduction, artificial nests were inserted into the tank made on the bottom with ballasted polyethylene pipes, 50 cm long with a diameter of 20 cm. Fishes were fed on alternate day manual shedding commercial feed. Despite an insignificant mortality, the fish are sold when they reach a weight between 2 and 2.5 kg, allowing to control the density in the tank. A high density can cause that bigger fish become predator of the others. The small entrepreneurial reality of the fish farm has allowed to create three new jobs in the village.

Favored by a rural economy still largely based on the bartering of goods and services, a series of artisanal activities were born in the villages with the aim of having fish in exchange. Three tailoring and fabric processing activities were born.

The production of concrete blocks for the construction of the *barrage* has allowed the specialization of some inhabitants. Two of them, in particular, have started production (through manual molding) and sale of the blocks to other villages for a total of 10,000–12,000 blocks per year.

Some of these activities are still very fragile and highly dependent on the stability of the retail market. Unfortunately, the recent unpredictable pandemic events have led to a significant reduction in the demand for fish farm products in neighboring markets, leading to the loss of fish stock already in the tanks. The pandemic has highlighted the fragility of entrepreneurial activities undertaken in these contexts that have to face a much higher entrepreneurial risk than elsewhere.

#### **5. Conclusions**

The water crisis in Sub-Saharan African countries, and specifically in Mali, is not a new phenomenon but in recent years has taken on characteristics with geopolitical and international implications. The ongoing climate changes highlight the dramatic consequences of water scarcity: absence of health and hygiene, malnutrition especially in children, with increased mortality rates in under-fives, and the constant decrease in arable land. These factors increase political instability and determine the incessant escalation of revolts, and popular uprisings often linked to international terrorist groups. In these conditions, migratory flows can only intensify, expanding the scope of the phenomenon and establishing the need for international intervention.

To solve the water issue it is necessary to promote the self-construction of small local infrastructures such as *barrages* and to simplify the unnecessarily complex and articulated state management and regulatory systems.

The three-year research project led by the Department of Architecture of Roma Tre University, in collaboration with the University of Florence and in partnership with the Onlus *Gente d'Africa*, *Romagna Acque Società delle Fonti* Ltd. and AES *Architettura Emergenza e Sviluppo*, has led to the reconstruction of two damaged and no longer operating *barrages*, in the Kayes region, near Kita.

The operational phase of the project saw the participation of local communities and the involvement of municipal authorities brought together to restore the functionality and increase the performance of two small and damaged infrastructures.

The research project encompassed a series of on-site missions involving information gathering, surveying, prospecting, design, manufacturing, construction and the collection and dissemination of results. The reconstruction of the basins produced several indirect benefits. These range from improved cohesion of local communities to the increase in microbusiness activities related to the presence of water. In the current phase, the monitoring of the results is mainly aimed at assessing the environmental impact of the *barrages*, through the direct measurement of a series of basic environmental parameters and the indirect detection of the improvement of the living conditions of humans and animals.

**Author Contributions:** All authors wrote the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** The research was supported by Romagna Acque Società delle Fonti Ltd., Gente d'Africa onlus, Roma Tre University, AES Architettura Emergenza Sviluppo.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** A heartfelt thanks to Sara Negroni, Mauro Foli, and Massimo Mantuano from *Gente d'Africa onlus,* And to Tonino Bernabè for *Romagna Acque Società delle Fonti*. A further heartfelt thanks goes to Diawoye Tounkara, local reference for *Gente D'Africa* but, above all, irreplaceable guide, and support in Malian territory. Finally, a special thanks to the students who took part in the various missions in Mali: Giovanni Baratta, Iacopo D'Orazi, Francesca Limongelli and Pietro Marinari.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

### *Article* **Groundwater Resources Assessment for Sustainable Development in South Sudan**

**Manuela Lasagna 1,2 , Sabrina Maria Rita Bonetto 1,2,\* , Laura Debernardi 1, Domenico Antonio De Luca 1,2 , Carlo Semita 1,2 and Chiara Caselle 1**

Received: 29 May 2020; Accepted: 8 July 2020; Published: 10 July 2020

**Abstract:** The economic activities of South Sudan (East-Central Africa) are predominantly agricultural. However, food insecurity due to low agricultural production, connected with weather conditions and lack of water infrastructure and knowledge, is a huge problem. This study reports the results of a qualitative and quantitative investigation of underground and surface water in the area of Gumbo (east of Juba town) that aims to assure sustainable water management, reducing diseases and mortality and guaranteeing access to irrigation and drinking water. The results of the study demonstrate the peculiarity of surface and groundwater and the critical aspects to take into account for the water use, particularly due to the exceeding of limits suggested by the WHO and national regulation. The outcomes provide a contribution to the scientific overview on lithostratigraphic, hydrochemical and hydrogeological setting of a less-studied area, characterized by sociopolitical instability and water scarcity. This represents a first step for the improvement of water knowledge and management, for sustainable economic development and for social progress in this African region.

**Keywords:** water resources; sustainable management; local development; water for food security

#### **1. Introduction**

Environmental sustainability plays a major role in the United Nations (UN) Agenda 2030 for Sustainable Development. In this framework, the balance between protecting environmental resources and satisfying social and economic needs has become a key development issue.

The global variety of ecosystems and landscapes and the different accessibility to natural resources contribute to shaping social and economic factors, which affect the development of local territories and communities, providing special inputs to their economic growth and resilience. The critical relationship between economic development, growth and environmental protection, if not reconciled in sustainable ways, risks causing the depletion of natural resources.

In South Sudan, as in several Sub-Saharan African countries, environmental conditions are often vulnerable to several shocks (climate, population growth, human activities impact, conflicts and security), which may produce heavy effects on their development.

Many development projects, such as the project "Women Empowerment and Sustainable Agricultural Development to Achieve Food Security in South Sudan (WOSA) AID 10915" funded by the Italian Agency for Cooperation and Development (AICS), support the sustainable management and use of natural resources through actions for protecting water, air and soil, and for preserving biodiversity and combating desertification, including the elaboration and implementation of measures

for mitigating the effects of climate change and for fostering resilience. Other important activities concern the energy and infrastructure sector, which includes transportation and water networks, the distribution of electricity generated by renewable resources and the broad sector of territorial planning.

In developing these approaches, the environmental characterization is promoted to identify landscape character types, geological stratification, biogeographical regions, etc. The recognized spatial frameworks would be useful in assessing interventions and impacts of policies to ensure local food security, social development and sustainable natural resources management. This information should be shared with local administrations, with the scientific community and with any organization that operates in the area.

The economy of South Sudan (East-Central Africa) is predominantly agrarian, with almost 60% of the total workforce engaged either directly or indirectly in agriculture. However, this sector remains underdeveloped due to the political instability of the country and the primitive method of farming systems. Food insecurity is a major problem due to low agricultural production connected with weather conditions and lack of water infrastructure and knowledge [1].

For these reasons, the present study aims to propose an analysis of the local hydrogeological framework in order to answer to the main needs linked to the deficit in the food production and to guarantee a sustainable access to irrigation and drinking water, reducing diseases and mortality.

The study focuses on the city of Gumbo, located at the east side of Juba town. Juba is divided into three sub-districts named Sherikat (Central Gumbo), Jebel Lemon (east of Gumbo) and Adodi (North-West Gumbo). The population of Gumbo is roughly 5000 households, and more than 70% of the population depends on agriculture. About 80% of the population comes from different parts of the country, particularly from east side of Juba. They are internally displaced persons or refugees as a result of the civil war, which broke out in December 2013, and its impact.

The aim of this work is to provide a hydrogeological, lithostratigraphic and hydrochemical reconstruction of the area. These activities are useful for programming drilling campaigns of new wells and in defining sustainable uses or interventions for water according to the quality [2–10]. The shortage of previous studies in the area, also due to the long civil war that occurred in the region in recent years, makes particularly important the collection and the organization of available scientific knowledge on the territory and the execution of new studies to fill the gap of data at the local scale. This may help to create a database for the necessary future interventions that have to be planned in the area.

The study is organized as a first collection of geologic and hydrogeological data of South Sudan, starting from the scarce literature that was completed with a more detailed lithostratigraphic and hydrogeological analysis, specifically focused on the area of Juba.

#### **2. Material and Methods**

#### *2.1. Collection of Information on the Study Area from the Scientific Literature*

The collection of geological and hydrogeological information on South Sudan started from the scarce available scientific literature and brought to the reconstruction of a general framework of the climate, the vegetation and the regional geological and hydrogeological setting. The absence of more detailed data at the local scale was filled with a lithostratigraphic, hydrogeological and hydrochemical reconstruction in the area of Juba, the capital of South Sudan. Specifically, the proposed study focuses on an area surrounding Gumbo (Central Equatoria—Payam Rajaf) (Figure 1), which is located in a flat plain at a distance of about 1.5 km eastwards from the Nile River, referred to here as the "White Nile".

**Figure 1.** Location of the study area (modified from [11]).

#### *2.2. On-Site Survey*

#### 2.2.1. Lithostratigraphic Reconstruction

The lithostratigraphic reconstruction was conducted combining data from a geophysical survey, performed in August 2017 by the United Drilling Company, and from the execution of four new wells drilled in 2018.

The geophysical survey was implemented in an area suffering from lack of water (Figure 2). It consisted of two vertical electrical soundings (VESs), which provided an insight into both thicknesses and types of the overburden strata and of the presence of fractured bedrock, based on resistivity contrasts. VESs were conducted using potential electrode spacing (MN/2) of 0.5 and 5 m, reaching a depth of about 50 m.

#### 2.2.2. Hydrogeological Reconstruction

The new wells were drilled in areas where people lived without free access to water for human, agriculture and livelihood consumption (WPC, W1, W2, W3 in Figure 2). The depth of wells ranges between 60 and 90 m. Stratigraphic logs and water table levels (meters below ground level, m b.g.l.) contribute to the stratigraphic and hydrogeological reconstruction. Water table levels of spring–summer 2018 were interpolated to create a preliminary water table map, indicating the main flow direction of groundwater.

#### 2.2.3. Hydrochemical Analyses

The reconstruction of the hydrochemical setting was performed through two sampling campaigns, conducted in August 2017 (1 water sample, called WPC) and July 2018 (6 water samples). This second campaign includes both groundwater samples (W1, W2 and W3) and surface water samples, taken from seasonal streams (S1, S2 and S3) (Figure 2). Due to the political instability, military checkpoints conditioned the mobility of persons and vehicles, limiting the access to many areas, particularly along

the main streams. Hence, the sampling was only performed for the new drilled wells (groundwater) and areas of free access (seasonal streams samples).

The chemical analyses, performed by the Nuovi Servizi Ambientali (NSA) laboratory in Robassomero (Turin, Italy), included a first step of assessment of data quality, which was accomplished by calculating the balance of positive and negative ions. Water fulfils the principle of electroneutrality and is therefore always uncharged. The level of error was calculated by using the following formula [12]:

• Error of ion balance = ((Σcations − Σ anions) / (Σcations + Σ anions)) \* 100

An error of up to ±5% was considered as tolerable. The results of chemical analyses were then displayed through a Piper diagram.

Since water from wells and seasonal streams is currently used for human consumption, the chemical results were compared with the limits established by the regulations in force in South Sudan and the WHO regulations to provide information on the quality of water in the study area. More specifically, the following regulations were considered:

**Figure 2.** Location of the water samples taken for hydrochemical analyses (wells and seasonal streams) and vertical electrical soundings (VESs).

#### **3. State-of-the-Art Knowledge in the Study Area**

The state-of-the-art geological and hydrogeological knowledge in South Sudan only includes general studies, at the regional or even national scale. The purpose of this review is to collect of all the available information, creating a solid framework on which setting up a more detailed local-scale dataset proposed in this study.

#### *3.1. Climate and Vegetation*

The average altitude of South Sudan is 470 m above sea level, with a gentle slope to the north.  As regards to the annual distribution of precipitation, the rainfall over the River Nile basin is characterized by highly uneven seasonal and spatial distribution. Most of the basins show only one rainy season, typically in the summer months. Only the equatorial zone has two distinct rainy periods. The probability of occurrence and volume of precipitation generally declines moving northwards, with the arid regions in Egypt and the northern region of Sudan receiving insignificant annual rainfall [14]. The area of Juba (specific object of this study) is in a sector characterized by a total rainfall (average annual for the period 1960–1990) between 900 and 1200 millimeters (Figure 3).

**Figure 3.** Average annual rainfall for the period 1960–1990 in South Sudan [14] and location of the study area. The orange line borders the River Nile Basin.

For a detailed description of the study area, data of the weather station in Juba [15] were collected and analyzed. The climate of Juba is tropical with average yearly temperature between 33.8 and 20.7 ◦C. Maximum temperature is during February–March, and minimum temperature is during December–January (Figure 4). The rainy season is from May to October. The dry season starts from November and ends in March and occurs particularly in January and February. Average yearly total rainfall is 974 mm. (Figure 5). The highest number of rainy days occurs from April to October, whereas the lowest number of rainy days are reported in January. The average annual number of rainy days is 104 (Figure 6).

**Figure 4.** Monthly average minimum and maximum temperature of Juba [15].

**Figure 5.** Monthly precipitation of Juba [15].

**Figure 6.** Average monthly rainy days over the year of Juba [15].

Across the Nile region, actual and potential evapotranspiration vary markedly [14]. Seasonal/ monthly variability of evapotranspiration is indeed a function of temperature, wind speed, relative humidity, solar radiation and biomass production. More specifically, the study area is located in a sector characterized by a potential evapotranspiration (average annual for the period 1960–1990) between 1600 and 1800 mL per year (Figure 7).

In the study area, the type of vegetation is biologically diverse, and it is not generally very dense. Examples of common trees are teak, shrubs and mango trees.

The rate of weathering is very high due to the combination of both high temperature and rainfall. This condition facilitates hydrolysis, oxidation and reduction and physical types of weathering such as the action of the plant's roots.

**Figure 7.** Average annual potential evapotranspiration for the period 1960–1990 [14] and location of the study area. The orange line borders the River Nile Basin.

*3.2. Geological Setting*

The geological setting of South Sudan comprises three main geological frameworks [16–18]:

The basement complex is dominated by Proterozoic rocks of medium to high metamorphic grade, with isolated areas of probably older higher-grade granulitic rocks. In broad terms, the Proterozoic metamorphic basement comprises three main units: (i) variably banded and foliated granitic gneiss and migmatites (basement complex, dominantly banded magmatic gneiss in Figure 8), (ii) biotite-amphibole schist/amphibolites and (iii) calcareous meta-sediments and quartz meta-sediments (basement complex, dominantly schists and metasediments in Figure 8).

The crystalline basement complex hosts the majority of mineral occurrences. However, the recorded mineral presence is limited, because the country lacks a significant mineral resource evaluation.

Effusive basic volcanic rocks, mainly basaltic lava and tuffs, are found in the south-eastern part of the country (Rocks volcanics, mainly basalts in Figure 8) and are related to the activity of the East African Rift system.

The Neogene sequence comprises unconsolidated sands, gravels, clay sands and clays (Umm Rwaba Formation in Figure 8) characterized by rapid facies changes. Conditions of deposition of the Umm Rwaba formation are fluvial and lacustrine, with sediments laid down in a series of land deltas similar to those existing in present day South Sudan. The age of sediments is considered to range from Tertiary to Quaternary [19]. This formation hosts most of the ongoing oil exploration activities, and numerous holes/wells were drilled through the cover into the underlying basins. According to oil exploration data from Central and Southern Sudan, the maximum drilled thickness of the Umm Rwaba Formation is higher than 4600 m. According to geophysical data, the maximum recorded thickness is higher than 8200 m in some places [16].

Extensive alluvial deposits underlie the flood plain of the Nile and many of its tributaries within the study area and toward the north of Juba.

**Figure 8.** Map of the geology and mineral deposits of South Sudan [20] and location of the study area.

The Juba area is generally underlain by metamorphic rocks of the basement complex. The basement complex is overlain unconformably by alluvial and surficial deposits that vary in thickness from one location to another. In detail, the basement complex of Juba is composed of gneiss that ranges from medium to high grade metamorphism. Both banded and unbanded gneiss occurs in the area; different types such as augen gneiss, grey gneiss, etc., are present. The gneiss is intruded by several doleritic, gabbroic and granitic intrusions that occur as plutons, or doleritic, gabbroic dikes with east–west trending. The rocks in the study area are mildly deformed. The geological structures consist of both ductile structures, which include folds, foliation and crenulation cleavage, and structures with joints and faults.

Effects of weathering, due to the tropical climate of the area, can be seen in the change of surface color (usually dark or reddish brown) of most rocks, exfoliations and other types of physical weathering.

Close to the Nile River and its tributaries, the geology of the area is dominated by recent alluvium, terraces, deltas and swamp deposits.

#### *3.3. Hydrogeological Setting*

As shown in Figure 9, three different hydrogeological sectors may be identified in South Sudan, based on the structure of aquifers and on the recharge rate [14,21]:

**Figure 9.** Sketch of the structure and recharge rate of the aquifers [14]. The orange line borders the River Nile Basin. The red circle indicates the study area.

The study area is located in a sector with local and shallow aquifers; the groundwater recharge rate is between medium and very low.

The shallow aquifers are usually located in the overburden or in a fractured upper part of the bedrock. The recharge of shallow aquifers is generally dependent on the size of the catchment area and the lithological character of the overburden.

In the study area, the cover sequence may contain a phreatic aquifer if constituted by coarse deposits (gravel, sand, pebble) of a large thickness. Groundwater in the basement formations generally occurs in the weathered (overburden) and fractured rocks. Weathered rocks, indeed, may have a good transmissivity and storage. However, the best aquifers are generally found at the contact zone between the overburden and the rocks. This zone has fewer secondary clay minerals, resulting in a higher transmissivity. Lastly, the highest yielding aquifers can be expected in the fractured bedrock. Boreholes are usually drilled into the fractured bedrock where the permeability is high and where the storage can be provided by the overburden. Fractured aquifers may be recharged through a connected system of fractured zones.

The hydrography of the study area consists of the Nile River and several other streams connected to the Nile River.

#### **4. Results of the On-Site Survey**

#### *4.1. Lithostratigraphic Reconstruction*

The analysis of the stratigraphic logs of the four new drilled wells (Figure 10) highlighted the presence of a clayey and sandy soil on the surface, with a thickness between 1 and 8 m, followed in depth by an alternation of non-fractured granite layers and altered wet granite or fractured granite.

**Figure 10.** Stratigraphic logs of four new wells (not to scale).

The wet granite has a thickness of 2 to 5 m and is located at a depth ranging between 10 and 20 m. The first level of fractured granite has a variable thickness of 2 to 10 m and depth ranging between 18 and 35 m. The second level of fractured granite has thickness of 2 to 6 m and depth ranging between 24 and 65 m.

The screens are mainly positioned in the granitic basement along the entire depth of the wells, with the exception of well W2, which also catches water from the overburden, suggesting the role of both the overburden and bedrock as local aquifers.

The two VESs performed near to the WPC well enabled the identification of layers with homogeneous resistivity (Figure 11). VES1 has slightly lower apparent resistivity values than VES2, but their results are coherent. More specifically, they show the presence in the subsoil of three main layers with different thicknesses and apparent resistivity. In general, the data show the existence of a first layer, with a thickness of about 2 m, characterized by intermediate resistivity that is followed in depth by a second layer with low resistivity, up to about 20–25 m. The resistivity profile ends with a third layer with high resistivity and up to 50 m of depth.

**Figure 11.** Graph with the results of the two VESs and their elaboration.

#### *4.2. Hydrogeological Reconstruction*

Table 1 reports the position, depth and diameter of the wells and the respective water level measurements. The depth of water table ranges between 8.0 and 24.3 m b.g.l. (i.e., piezometric level between 456.0 and 468.7 m a.s.l). The direction of groundwater flow is predominantly SSE–NNW, in the direction of the White Nile, which serves as a drainage axis of the entire surrounding plain sector.

**Table 1.** Data used for the piezometric reconstruction (spring–summer 2018).

Figure 12 reports the resulting water table map. Since the piezometric reconstruction is based on only four wells, the map only indicates the main direction of groundwater flow.

**Figure 12.** Water table map for spring–summer 2018. Due to the scarce data, the map gives indicative information about the hydraulic gradient and groundwater flow direction.

#### *4.3. Hydrochemical Analyses*

Table 2 reports the results of the water chemical analyses. The error of ion balance was always less than ±5%, and consequently it was considered tolerable. Table 2 also reports the comparison with the limits established by the regulations in force in South Sudan and the WHO regulations, providing information on the quality of water for human consumption in the study area.

Results show that both the content in individual elements and the total mineralization are very variable, depending on the analyzed sample. In general, however, surface water from seasonal streams has lower electrolytic conductivity and chloride levels.

The WPC groundwater sample, taken in 2017, shows different chemical features when compared to groundwater samples taken in W1, W2 and W3 wells in 2018. The latter, indeed, have higher heavy metal content. This difference is probably due to the different positions of screens in the wells and thus to the different sampled aquifers.

The limit value of total hardness of the South Sudan regulation (200 mg/L) is only respected in samples W3, W2 and S2, whereas the W1, S1 and S3 exceed it.

The single ions exceeding the suggested limits by the WHO and national regulation that may assume negative effects for human health in the long term and negative consequences for the soil in case of agricultural use are chromium (according to WHO limits) and sodium, fluorides and manganese (with regards to the South Sudan legislation limits).

**Table 2.** Results of chemical analyses and comparison with permissible limits for the South Sudan legislation and WHO guidelines for drinking water quality. The parameters exceeding the permissible limits for the South Sudan legislation are in light blue; those that exceed the WHO guidelines for drinking water quality are in red (N.M. = not measured).

The levels of sodium are usually higher in groundwater than in surface water. WPC, W1, W3 and S3 have sodium concentrations slightly higher than South Sudan limits.

Greater attention must be paid to fluoride, which presents medium–high concentrations (between 800 and 1400 μg/L) in water samples W1, W2, W3, S2 and S3. High fluoride levels may cause damage to bones, kidneys and teeth.

Manganese is usually found in concentrations less than 10 μg/L, with the exception of wells W1 (55.9 μg/L) and W2 (469 μg/L, greater than the South Sudan legislation limit).

The hexavalent form of Chromium, which is very toxic and carcinogenic to humans, is always less than 3 μg/L. On the contrary, the trivalent form, that is not carcinogenic, is present in concentrations higher than the WHO limits for the samples W1, W2 and S3.

To clarify the distribution of parameters exceeding the permissible limits, Figure 13 reports the samples with a content higher than South Sudan national legislation and WHO guidelines, specifying the water concentration.

**Figure 13.** Map of the distribution of the chemical parameters exceeding the permissible limits for the South Sudan national legislation and WHO guidelines for drinking water quality.

#### **5. Discussions**

The set of lithostratigraphic, hydrogeological and hydrochemical data collected with the on-site survey allowed a local framework for the distribution and the quality of the water resource to be defined.

The analysis of VES results and borehole logs coherently suggest the presence of a few meters of overburden (intermediate resistivity) followed by altered/fractured granite (low resistivity) up to 20 m depth and no fractured granite (higher resistivity) at a lower depth. Considering the depth of the wells and the reliability of information coming from direct geological investigation, the borehole logs suggest the alternation of fractured and non-fractured granite up to the end of the wells (60 to 90 m depth).

Based on this lithostratigraphic setting (overburden and igneous bedrock), Figure 14 proposes four possible hydrogeological scenarios. Data suggest the presence of local and shallow aquifers with medium to very low groundwater recharge rate. Phreatic aquifers are hosted in the coarse unconsolidated deposits or in the altered basement, whereas the local aquifers are associated with the fractured basement. The best aquifers are generally located at the contact zone between the overburden and the rocks and in the fractured rocks of the bedrock, which hosts the highest yielding aquifers.

**Figure 14.** Possible scenarios for wells drilled in locations similar to the Gumbo area from a lithostratigraphic–hydrogeological point of view.

This conceptual model is coherent with the hydrogeological framework at the national scale retrieved from the available literature [14,21], which identifies the major aquifers in the northern and in the eastern parts of the state (i.e., on the borders with Sudan and Ethiopia), where the geological setting describes the presence of thick fluvial and lacustrine deposits. The southern and western parts of the region, where the Gumbo area is located, mainly consists of granite and other crystalline rocks, only creating the conditions for local and shallow aquifers. As a consequence of this general assessment, the report [22] describes a difference in the potential between the northern and eastern aquifers and the ones in the south and west wide areas of the country. The former are described as excellent aquifers, with high potential mainly depending on the depth and the good permeability properties of the deposits; the latter, being located in areas characterized by the presence of the basement complex, are described as low potential aquifers, of which yield of groundwater is only enough for rural or urban water supply.

In this hydrogeological framework, despite a general low expected productivity, the local conditions may allow water production to be optimized if the drilling is performed in accordance with the conditions defined as "Productive borehole in fractured zone" (Figure 14), where the boreholes are drilled both in the overburden and fractured bedrock and the latter is characterized by layers of high permeability due to alteration (altered basement complex) or fractures (fractured basement complex). The storage can be provided by the overburden.

The hydrochemical characterization of surface and groundwater is a complete novelty in the panorama of available data on South Sudan. The results furnish the main chemical features of water of the area, normally used for human consumption, irrigation and livelihood.

The data registered a local exceeding of the suggested limits, with assumed possible negative effects for the human health in the long term and negative consequences for the soil in case of agricultural use, for chromium, sodium, fluorides, manganese and total hardness. In general, surface water, coming from seasonal streams, highlighted a lower water quality and scarcer and more ephemeral discharge. Indeed, even if it represents the most direct, cheapest and most easily obtained water resource for humans and animals, it shows higher vulnerability to biological and chemical pollution and is easy to contaminate by anthropic input. Hence, the best supply is represented by groundwater.

Even if the number of samples is very low, some considerations of the relationship between single parameters were made. Chlorides vs. sodium, sodium vs. electrolytic conductivity and chlorides vs. electrolytic conductivity graphs show in general good correlations for surface water (Figure 15).

**Figure 15.** (**a**) Chloride vs. sodium graph (meq/L); (**b**) electrolytic conductivity vs. chlorides graph; (**c**) electrolytic conductivity vs. sodium graph for the surface analyzed waters.

New data have to be added in order to verify the indicative trends obtained.

Chemical data were also plotted in the Piper diagram, allowing for a classification of groundwater and surface water in chemical facies and for a simultaneous comparison of different water samples. The Piper diagram (Figure 16) shows that the samples belong to the Na-HCO3 facies. These waters are typical of deep groundwater environments, influenced by ion exchange.

**Figure 16.** Piper diagram, showing hydrochemical facies of groundwater and surface water samples.

The Na-rich facies resulting from the Piper classification is coherent with the high concentration of sodium that slightly exceeds the national regulation in three groundwater samples out of four. The remaining sample (W2) has, however, an Na concentration of 98.8 mg/L (the limit is 100 mg/L).

Nevertheless, according to the experimental results, this high sodium concentration is not related to an equivalent abundance of chlorides (i.e., the correlation between sodium and chlorides is unbalanced in favor of sodium). The hypothesis of an anthropic contamination that could be considered in presence of salty waters (i.e., similar concentrations of Na and Cl) seems therefore to be unsuitable in this case, suggesting, rather, a natural origin. The described geological framework, reporting a regional bedrock mainly consisting of granite rocks rich in Na minerals (e.g., albite and Na feldspars) supports this hypothesis. Similar results and conclusions were obtained by the author of [23], who proposed an analysis of the water pollution in Sudan (i.e., in the northern geographical position with respect to our study area) and observed a prevalence of sodium bicarbonate water facies where the aquifer was in contact with the rock basement.

A similar natural origin of water pollution may be suggested for the fluorides that exceed the national regulation limits in the majority of the samples. Fluoride was, indeed, described as one of the most important natural pollutants of water in Africa [24] as a consequence of volcanic activities, presence of thermal waters, gases emissions and granitic and gneissic rocks. These natural conditions are often enhanced by low pumping rates, which increase the contact time and favor water–rock interactions, resulting in higher fluoride releases in groundwater [24,25].

As already stated, the concentration of total chromium, which exceeds the WHO limits in three of the samples, is related to a low percentage (<5%) of hexavalent chromium (i.e., the chromium form usually linked to anthropic contamination and more dangerous for the human health). This suggests, again, a natural origin of the contamination connected with lithological setting (i.e., presence of granite or gneiss rocks)

The last anomalous record in the results involves sample W2, which has a content of manganese that slightly exceeds the national regulations and is significantly higher than in all the other samples. Since the depth of the W2 well is not significantly different from the others, this anomalous concentration should be attributed to local conditions. The absence of nitrates and sulphates and the low electrolytic conductivity that characterize this water sample suggest the existence of a reducing environment, possibly connected to an organic contamination that progressively introduces a dissolution of manganese (and iron) already present in the surrounding rocks.

#### **6. Conclusions**

The groundwater resources of a country are crucial for the development of several economic sectors. In semi-arid and arid environments, groundwater enables millions of human beings and animals to exist in terrains that would otherwise be uninhabitable.

The General Assembly of the United Nations published the document "Transforming our world: the 2030 Agenda for Sustainable Development" as a result of the UN summit for the adoption of the post-2015 development agenda. In terms of the Sustainable Development Goal target for drinking water, Sustainable Development Goal (SDG) target 6.1 is to "achieve universal and equitable access to safe and affordable drinking water for all by 2030".

The availability and quality of water, besides representing a fundamental resource as drinking water, is necessary for a good development of agricultural and breeding activities and, consequently, for a sustainable development of the local economy. The water shortage, together with the great frequency and severity of drought periods and the excessive heat conditions, often causes agricultural vulnerability in arid or semi-arid areas of Sub-Saharan Africa. These conditions of vulnerability are enhanced by the global climate changes of recent years, the effects of which are expected to be large and far-reaching predominantly in the developing world [26,27].

For these reasons, the present study proposes an investigation of the lithostratigraphic and hydrogeological setting of the Gumbo village (SE of Juba) to make water extraction systems available and ensure their sustainable management to guarantee food security and economic independence for the populations in the area. Due to the political and social instability, the possibility to move and work in the field during the project was negatively affected, implying the difficulty of collecting data and water samples. Nevertheless, considering the scarce scientific and technical literature available for South Sudan, the collected data and proposed interpretations represent a first fundamental step for the characterization of the Gumbo area. The results contribute to defining a conceptual hydrogeological model and the critical aspects to take into account for the water use in the sampled sites.

In any context, the knowledge of the hydrogeological and hydrochemical setting is an important prerequisite for a risk-informed management of water resources. The planning of hydrogeological-based interventions may guarantee a wide access to good quality water for the local population for drinking, irrigation and livestock purposes. This study represents, therefore, a fundamental step to ensuring food security as well as sustainable economic development and social progress in this African region.

The collected data can be very useful for Administrative Local Authorities, recently established in South Sudan, as well as researchers and the local population, in order to improve water knowledge and management in this little-known area. Moreover, the implementation of a scientific dataset represents the first step toward sustainable economic development and social progress, helping to improve the livelihood of the rural communities and enhancing sustainable and environmentally friendly agriculture, soil conservation and remunerable livestock.

According to the Local Authorities, a survey program increasing the number of water points to monitor the quantitative and qualitative distribution of the water resource should help in better defining the local knowledge gained in the present study and consolidating the scenario that is

defined (higher quality of groundwater than surface water, "productive borehole in fractured zone" hydrogeological model and natural contaminations due to a geological setting with local increasing of exceeding parameters).

Future developments of the study may also include the long-term monitoring of the groundwater. The repetition of the analyses proposed in this study (i.e., measure of groundwater static level, hydrochemical analyses of surface and groundwater samples) at different times throughout the year, together with an increase of the number of sampling points, may allow for the assessment of the real potential of the water resource, with an evaluation of the influence of the seasonal variations on the resource availability. The temporal and spatial increment of collected samples would also contribute to validating the hydrogeological model, with an improved understanding of the flow directions and of the relations between groundwater and surface waters.

Further information should moreover include socioeconomic and demographic data (population, land use, cultivated crops, livestock activities, etc.) of the study area to better understand the various human needs for water to neither exhaust the water sources and the local economy nor have long term negative impact on the environment.

In addition, the monitoring of the chemical contaminations over time, possibly enriched with the local sampling of waters at different depths, may quantify the real danger related to each anomalous concentration and explain the distribution of the contaminations in the aquifer [28,29]. As a function of the specific use (e.g., drinking water, agriculture), the results of these analyses may help to assess the necessity and the features of interventions that may guarantee the safe use of the water resource.

In relation to the intended use of water for agricultural purposes, additional analyses may be specifically directed to the evaluation of the sodium adsorption ratio (SAR), which is a good indicator of the suitability of water for irrigation.

Due to the dry climate conditions of South Sudan, and of the Sub-Saharan African regions in general, another important development of the research could be the assessment of water resources' vulnerability to climate change [30]. An interesting approach to investigate this topic is the analysis of the water resource potential; after the selection of a number of target stations, the study should provide an estimation of rainfall amount on average over the last 30 years and a comparison of rainfall data and survey campaign outputs. The results would show whether the climate change affected the groundwater, with a quantitative evaluation of the entity of this influence on both availability and quality of the water resource [31,32].

A similar development of the research should represent the first step to defining Local Development Territorial Plans that the government needs in order to identify sustainable social and economic assessment (economic activities to encourage, territorial distribution of the refugees, stabilization or development of nomadism). It would be recommended for all decision-makers and politicians but also for rural development program managers to employ a similar approach, which emphasizes the knowledge of the characteristics of the territory and its specificities to deal with the management of natural resources, water in particular, in a sustainable way.

**Author Contributions:** Conceptualization, M.L. and S.M.R.B.; data curation, L.D., C.C. and C.S.; formal analysis, M.L. and S.M.R.B.; funding acquisition, S.M.R.B.; Investigation, L.D.; methodology, M.L. and S.M.R.B.; supervision, D.A.D.L.; visualization, C.C. and C.S.; writing—original draft, M.L., S.M.R.B., C.C. and C.S.; writing—review & editing, M.L. and S.M.R.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by AICS (Agenzia Italiana per la Cooperazione allo Sviluppo), OSC-2016 competition, grant number AID 10915/VIDES/SSD, Title of the project "Women Empowerment and Sustainable Agriculture Development to Achieve Food Security in South Sudan (WOSA)".

**Acknowledgments:** The authors thank Comina Cesare for his help in the interpretation of geophysical data.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

### *Article* **Water Resource Management and Sustainability: A Case Study in Faafu Atoll in the Republic of Maldives**

**Maurizio Filippo Acciarri 1,\* , Silvia Checola 2, Paolo Galli 3, Giacomo Magatti 4 and Silvana Stefani 5**

**Abstract:** This paper contributes to the existing literature in proposing an integrated approach to water management and energy renewable production in a fragile environment. After the 2004 tsunami, in many outer islands in The Republic of Maldives, the lens freshwater natural reservoir was deeply damaged. Currently, the populations of rural atolls use rainwater and water in plastic bottles imported from the mainland for drinking. To provide safe and sustainable drinking water, we analyze the feasibility of two different actions: a desalination system fed by a diesel plant or by a photovoltaic (PV) plant with batteries. The current situation (business as usual, (BAU)) is also evaluated and taken as a benchmark. After illustrating the technical and economic features of desalination and PV plants, a financial and environmental analysis is conducted on the two alternatives plus BAU, showing that the desalination fed by the PV plant results in optimization both on the financial and the environmental side. The levelized cost of water (LCOW) and the CO2 levelized emissions of water (LEOW) are calculated for each alternative. The case study is developed in Magoodhoo Island, Faafu Atoll and can be extended to other islands in The Republic of Maldives and in general to small island developing states (SIDS).

**Keywords:** photovoltaic energy; desalination system; SIDS; CO2 emissions; LCOW; LEOW

#### **1. Introduction**

Most of the small island developing states (SIDS), to which The Republic of Maldives (in short, The Maldives) belongs, share similar sustainable development challenges: a small but increasing population, vulnerability to external shocks, strong dependence on import trade, and a fragile environment [1]. Development is a need and many SIDS now recognize, as a primary objective, the move towards low carbon sustainable economies [1], while at the same time improving the standard of living of the local population.

Moreover, islands enjoy generally beautiful sceneries, fishing resources and unique natural settings that must be preserved and guaranteed for future generations.

As reported by the Asian Development Bank [2] in November 2020, the tourism industry comprises around 25% of the national gross domestic product (GDP) in SIDS. In [3], a road map establishes the guidelines to transition from a fossil-fuel-based energy sector to a cost-effective, business-competitive, affordable, and sustainable renewable energy. This scenario forecasts a continuous and sustained moderate transformation of the energy matrix that will result in 29% of fossil fuels being reduced compared to a business-as-usual situation. As recently reported by IEA [4], the share of renewables in global world electricity generation is nearly 28% in 2020, but there are important differences among countries.

**Citation:** Acciarri, M.F.; Checola, S.; Galli, P.; Magatti, G.; Stefani, S. Water Resource Management and Sustainability: A Case Study in Faafu Atoll in the Republic of Maldives. *Sustainability* **2021**, *13*, 3484. https://doi.org/10.3390/su13063484

Academic Editor: Maurizio Tiepolo

Received: 11 February 2021 Accepted: 15 March 2021 Published: 22 March 2021

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Even though it is almost universally recognized that renewable energies must gradually substitute fossil fuels [5], the use of renewables on small islands is still quite low based on high transaction costs and poor knowledge of the market potential [6].

Electricity is also dependent on imported fuel, and the level of CO2 emissions is quite high [7]. Taking the Magoodhoo island in The Maldives as a case study, our aim is to analyze an important issue: the coupled nexus water/energy, and to show that feasible solutions are possible, from the financial and environmental point of view.

Scarcity of energy and water are among the major drawbacks for SIDS [8]. This is particularly the case of many outer islands in The Maldives, where, since the 2004 tsunami, the lens freshwater natural reservoir has been damaged, leading to a significant increase in costs as well as an increase in the scarcity of drinking water.

In [9], an extensive review of the recent situation of SIDS is illustrated. Like many SIDS all over the world, The Maldives depends upon imported conventional sources of energy, and scarcity of water severely restricts economic and social development. As far as energy is concerned, the dependence on fossil fuels makes SIDS vulnerable to oil price rises with a significant impact on the local economy. Energy systems and water supply are closely coupled, and the nexus is particularly relevant in SIDS. The ultimate goal is to make SIDS independent from the mainland in energy and water. A desalination system, combined with renewable energy, can definitely be the solution for solving the scarcity of water and contributing to the reduction of pollution from fossil fuels.

In [10], 1087 islands are classified with the use of a cluster analysis according to climatic as well as physical and socio-economic parameters. The conjecture is that an energy supply system proven to be successful on one island could also be successfully implemented on another island.

From the literature analysis, it is quite evident that in SIDS, an energy transition to more sustainable energy sources is desirable and different studies state that the transition should take place in the next few years [11–25].

In The Maldives, energy sources are traditionally based on imported conventional supply, of which the most common fuel is diesel which fuels small power plants, often with low efficiency and heavy polluting. Due to the diesel production, emissions of CO2 into the environment are large and in the medium term may cause damages to the environment. Renewable resources are scarcely used. While solar water heaters are quite widespread, photovoltaic (PV) panels and wind plants are rare. In 2016, the total power generation from renewable energy was 6 MW. In the medium term, the government has planned to install renewable energy systems for up to 30% of the daytime peak load in all inhabited islands [26]. Thus, the efforts of the Maldivian government and local authorities are on implementing renewable systems. The aim is to transit from energy dependence to independence from the mainland.

Studies on energy, applied or theoretical, for the assessment and feasibility of renewable projects in SIDS are quite numerous; less numerous are studies and experiences in desalination combined with renewables.

An extensive study is carried on a reverse osmosis (RO) desalination plant, located in the Sinai Peninsula in Egypt, fed by conventional and unconventional energy sources in [27].

A project for a desalination plant of 1000 m3/day is proposed in the Tyra Island in Greece [28]. The report illustrates two case scenarios: solar and wind power, compared to diesel generators, feed a desalination plant. Diesel generators are used as back up in both cases.

In [29] the feasibility of desalination systems fed by PV or high concentration solar plants of medium and large size in Saudi Arabia is discussed as opposed to diesel as the source of energy. The cost of solar is still high given the heavy subsidizing of diesel in Saudi Arabia.

In Kaya et al. (2019) [30] an analysis based on the levelized cost of water indicates that the current thermal desalination methods used in Abu Dhabi should be substituted by solar PV systems and reverse osmosis (RO) technology for desalination.

Helal [31] explores the economic feasibility of three alternative configurations of an autonomous seawater reverse osmosis (SWRO) unit in remote areas of the UAE. Three different scenarios are proposed here for the powering system where the unit is driven either by a diesel generator, a PV-diesel hybrid system, or solely driven by solar panels without battery backup. This paper can be considered an interesting benchmark, as the low desalination plant dimension [20 m3/day] is comparable with our scenario.

The global average levelized cost of water (LCOW) from desalination plants could decline from around \$2.86/m3 in 2015 to \$1.25 by 2050 if solar, storage systems and other renewable energies are used to decarbonize the sector [32]. The researchers forecast that in specific regions of China, India, Australia, and the U.S., drinking water may cost less than a dollar.

An extensive report from IRENA [33] gives useful information on systems already functioning. Different renewable energy sources are proposed to reduce the environmental impact.

Mainly, studies are based on the use of wind turbines or solar plants, but there are also proposals where other renewable sources, such as sea currents, are used [34]. This application could be interesting particularly for some islands where the scarcity of drinking water is more severe.

A recent paper published in 2020 [35] reports a study about the economic, technical, and environmental impacts of different desalination system configurations (centralized or decentralized, components, and technologies) on transition plans to achieve a higher share of renewable energy and desalination supplies for regions facing water scarcity. The analysis forecasts a reduction of LCOW from the current value of \$2.19–2.46/m3 to \$0.79–1.01/m3 in 2040.

In The Maldives, scarcity and quality of water are relevant issues. Traditionally, Maldivians used lens freshwater from household wells for both potable and non-potable purposes. The elevation of the highest point in most islands is less than 2 m above sea level, so the freshwater lens thickness of each island is low. The use of rainwater for drinking began in 1978 due to a cholera outbreak. In 1995, the first municipal water supply project began its services. It started from the capital Malé and extended to other population centers, including all touristic resorts. A public water system became available to 49% of the local population and was fully operative by the end of 2017 [36].

However, many outer island populations still depend on collecting rainwater for domestic use, as in the study case illustrated in the present paper. Furthermore, recently and with increased frequency, the collected rainwater stores run out during the dry season, causing expensive emergency water supply from the mainland. Moreover, after the 2004 tsunami, the lens freshwater deposit was deeply damaged, and freshwater is now brackish. While tourist resorts and the city of Malé are all equipped with (thermal) desalination plants, in many outer islands, people use rainwater and a supply of bottled water imported from the mainland for drinking, rainwater for cooking and a small amount of lens water for washing, flushing and other purposes [26].

However, even though The Maldives shows a wide deficit in energy and freshwater resources, they have unique advantages in term of renewable energy (sun) with excellent radiation and seawater potential. An integrated approach to water management and renewable energy production can definitely improve the living in rural atolls and substantially reduce CO2 emissions.

In this paper, we also carried out a life cycle assessment (LCA) for the different solutions proposed. In the literature, different studies on LCA for water systems of different dimensions can be found [37,38]: in integrated urban water systems or for the specific analysis of plastic bottle impact [39].

A synthesis of the literature discussed here, for water desalination and energy source solution adopted, is reported in the discussion section. The data will be used as a comparison with our results.

This paper contributes to the gradual road to energy/water independence from the mainland by proposing a financial and environmental evaluation for the installation and maintenance of a desalination plant. The off-grid energy to the desalination system is provided by diesel or by a PV plant. Results in this paper show that a desalination system plus a PV plant with batteries is the optimal choice, as opposed to the use of diesel, and more feasible than the current scenario, both from the financial and the environmental point of view.