Taking into account the referred goals of efficiency improvement, cost reduction and environment protection, the use of management models is considered a valuable method to support harbor management and design (or new design) decisions. This approach allows to adequately manage the dredged material, in operation phase, with its use (e.g. beach nourishment) or its safe disposal. As well, in design phase, the hydrodynamic modeling enables to achieve a better balance in erosion and sedimentation rates, throughout optimized technical choices. The aimed performance improvement intends to minimize the dredging volumes, keeping the sediments within the system but, at the same time, keeping the waterways of the harbor in a safe mode for the vessels that use it.

This chapter presents a planning and management model of dredging using the geo-processing automatic GIS environment developed by the Portuguese harbor authority, which is intended to be an accessible and efficient tool to support technical options in dredging design. Additionally, the particular case of harbor of Portimão, where the referred methodology was implemented, is discussed. The present hydrodynamic situation of the estuary is characterized, using a tidal model and considering average flows of the river. Then, taking into account the plans for the harbor expansion, the hydrodynamic modeling of the new layout is presented. Using as a reference the current situation, a method to analyze the influence that the planned works will introduce into the estuarine hydrodynamics and, consequently, in the pattern of sediment deposition and erosion is also summarized.

### **2. Methodology**

causes, as a heavy storm, or due to human intervention, as the construction of a dock), a change

Sediment transport processes are subject to the influence of site conditions as the geological and geotechnical characteristics of the estuary basin bed and of the existing suspended sediments. So a good knowledge on sediment geotechnical properties (i.e. granulometry, mineralogy, resistance to erosion,) is important as they define the hydrodynamic velocity for which sedimentation occurs [2] due to the distinct dynamics of transport, and even interactions,

Depending on harbor emplacement, sediment movement is also controlled by the river flow and tidal and wave conditions [3]. When considering harbors located in estuarine areas, particularly in the terminal section where the tide occurs, the tide plays a more important role in solid transport patterns than the river flow itself. Nevertheless, a major factor in this situation is the estuary's tidal prism, which is the volume of water exchanged between mean high tide and mean low tide or the volume of water leaving an estuary at ebb tide. The available tidal prism is so dependent on the geometry of the basin in terms of surface area and mean water depth and also the tidal range, the frictional forces and, to a lesser extent, freshwater inflow. Therefore, the larger the tidal prism related to the river flow, the more determinant for the

Hence, to better understand estuarine sediment dynamics, it is relevant to study the existing topography, through reliable surveys performed, at adequate detail and scale, for each case location. The obtained data allows hydrographic modeling in order to relate hydrography

Estuarine locations, although provide natural safety and protection conditions to the establishment of harbors and other facilities, are prone to natural filling caused by the settlement of sediments. Consequently, periodic dredging is required to maintain navigation channels and harbors in a safe and usable way. Moreover, given the natural trend of harbor activities expansion, dredging works are also needed to improve the design depth for larger vessels access, to build new wharfs and piers, or to improve existing harbors or other facilities [1]. As stated above, changes to harbor layout entail changes in estuarine hydrodynamics; hence the dredging need rates are subject to alteration, namely, tending to increase. So, it is important, when planning harbor new layout design, to include methods to minimize hydrodynamics

Although dredging operations are essential, these have a significant economic impact, not only during the construction phase but also along the operation phase, due to maintenance works. In fact, in small harbors, it corresponds to almost 75% of all maintenance costs [4]. Moreover, dredging activities can also have adverse environmental impacts, either within the dredge area or the deposition site, as fine-grained fraction of sediment resuspension (increasing the turbidity of water), nutrients and pollutants dispersion, water column contamination, or ecosystem degradation (e.g. by burying the biological habitats). So, potential environmental effects and risks are imperative to ascertain and well manage through the implementation

in hydrodynamics and, consequently, in the sediment-erosion pattern will occur [1].

between cohesive sediments (mud) and of non-cohesive sediments (sand) [1].

sedimentation and erosion processes, in the estuary, is the tide and tide flow.

with hydrodynamics and thus attain the referred knowledge.

changes and to reduce dredging volumes.

32 Sedimentation Engineering

of adjusted containing or remedial measures.

In estuarine locations, dredging activities are a required procedure both in harbor design and, during operation stage, in harbor management. However, from economic and environmental standpoints, dredging can also cause adverse effects related to the sediment removal from the basin bottom and also related to the management of the dredged material that are important to control. The referred impacts result from changes in local hydrodynamics and as consequence in the existing sedimentation-erosion patterns and rates.

An adequate management system that keeps the harbor in a safe and usable way, but also that controls the dredging impacts, reducing to a minimum the dredged volumes and disposing them, if possible and useful, within the system is so aimed.

In order to achieve those goals, it is essential to have a comprehensive knowledge of the present situation (reference situation) in terms of accretion and erosion areas and the typology (grain size) of the sediments within those areas. This data is attained through the combined analysis of local hydrography and hydrodynamics, as well as local geology and geotechnical characteristics. As a result, predictive models can be established, and better technical choices concerning harbor design or management are then possible.

• M1—conversion of CAD entities into vector entities (GIS shapefile).

• M3—interpolation of particle sizes, deterministic method IDW.

• M4—preliminary zoning of sediments of harbor areas.

planning.

in harbors.

for dredging purposes.

• M2—development of digital terrain models from bathymetry (DTM), tin and raster.

• M5—calculation of areas and volumes of erosion and deposition for subsequent dredging

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 35

So, the integration of the flow field pattern and tides, using finite element method (FEM), with size distributions in estuarine sediments (determined with MAZD), identifying their source, allows then to divide the harbor area in main areas, according to the same sediment typology,

**Figure 1.** Flow chart of the developed procedure of physicochemical characterization for sediment dredging management

Therefore, a set of procedures were established to aid and simplify both the planning of harbor dredging and of the disposal of the dredged materials. Some guidelines are then proposed to be followed [3–5]:

#### **2.1. Physicochemical model development**

Aiming an optimized dredging project management tool, the Portuguese harbor authority has developed and implemented a model of planning and management of dredging using the geo-processing automatic GIS environment which is next presented. Taking into account geo-referenced detailed hydrographical surveys and physicochemical analyses of the sediment, the referred model:

allowing then the zoning of the area to be dredged.

The developed analysis system is based on a conceptual model of morph-dynamic and multitemporal sediment distribution in port areas, automating the production of maps [6].

Through the conversion of different data formats, the proposed model is able to:

This system was implemented by applying Model Builder software ArcGIS ® (ESRI), and it consists of a set of tools that operate sequentially in the calculation of the various components of the model.

Firstly, **Figure 1**, five modules (defined as M1–M5) were implemented, each with specific processes to build automatic digital maps with the relevant information allowing [4–7]:

characteristics. As a result, predictive models can be established, and better technical choices

Therefore, a set of procedures were established to aid and simplify both the planning of harbor dredging and of the disposal of the dredged materials. Some guidelines are then pro-

• Analysis of the maximum velocities of tidal flow and its comparison with average tide and

• The use of this information in harbor dredging planning, including the definition for

Aiming an optimized dredging project management tool, the Portuguese harbor authority has developed and implemented a model of planning and management of dredging using the geo-processing automatic GIS environment which is next presented. Taking into account geo-referenced detailed hydrographical surveys and physicochemical analyses of the sedi-

The developed analysis system is based on a conceptual model of morph-dynamic and multi-

**iii.** Assess the areas and volumes of eroded and deposited sediments considering four dis-

This system was implemented by applying Model Builder software ArcGIS ® (ESRI), and it consists of a set of tools that operate sequentially in the calculation of the various components

Firstly, **Figure 1**, five modules (defined as M1–M5) were implemented, each with specific pro-

cesses to build automatic digital maps with the relevant information allowing [4–7]:

• Identifies the spatial distribution of zones where erosion and sedimentation occur • Relates them with the existing types and concentrations of contaminants (if any)

temporal sediment distribution in port areas, automating the production of maps [6].

Through the conversion of different data formats, the proposed model is able to:

**i.** Generate surfaces of different particle sizes by using interpolation methods.

• Analysis of the granulometry of sediments in the harbor area of the estuary

• Comparison of the sediment size with the maximum velocities of tide

concerning harbor design or management are then possible.

posed to be followed [3–5]:

34 Sedimentation Engineering

dredged material

ment, the referred model:

**ii.** Zone the dredging area.

of the model.

living waters flow velocities

• The use of automatic geo-processing

**2.1. Physicochemical model development**

allowing then the zoning of the area to be dredged.

tinct particle classes: pebble, sand, silt and clay [4].

• M5—calculation of areas and volumes of erosion and deposition for subsequent dredging planning.

So, the integration of the flow field pattern and tides, using finite element method (FEM), with size distributions in estuarine sediments (determined with MAZD), identifying their source, allows then to divide the harbor area in main areas, according to the same sediment typology, for dredging purposes.

**Figure 1.** Flow chart of the developed procedure of physicochemical characterization for sediment dredging management in harbors.

### **2.2. Zoning (M4)**

Following the physicochemical characterization and analysis of the sediments and taking into account the obtained results, the proposed methodology aims the identification of areas of erosion and deposition of materials.

in Silves, 13 km upstream. At present, the port area only encompasses the frontier stretch of the city of Portimão, and it can be seen that, upstream of the first Arade Bridge, the river can only be used by small tourist boats and in certain places only at high tide. Two breakwaters protect the entrance to the port, with a minimum of 200 m wide, followed by a 150 m wide navigation channel, which extends to the commercial wharf and the fishing port [9]. The W and E quays have lengths of 820 m and 680 m, respectively. In the wide front, there is a circular and maneuvering basin. On the right bank, from the inlet upstream, first there is Portimão Marina; then the Navy Pier, with a length of about 200 m; and the Terminal of Passengers and General Cargo, about 340 m long; further upstream, in a lower depth zone, there are other docks and berths for recreational craft. The fishing port is located on the left bank, with mooring wharves, a shipyard and a supply pier. The port of Portimão is used for trade, cruising, fishing and recreation. There is a weekly ferry link to Madeira and the Canary Islands.

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049

The modeling of the estuary of the River Arade includes the west coastal zone up to Ponta da Piedade, west of Lagos and the east coastal zone till near Vilamoura. Given the referred coast extension, it was intended to ensure that the tide conditions that were taken into account at the entrance of the bar would be free of undesired influences from the boundary conditions. Regarding the study area towards the inland, the river Arade was considered as far as the Roman bridge of Silves, in an extension of 13 km, and the Odelouca stream to a section about 14 km upstream from the mouth of the Arade. This way, it was intended to obtain, in the area under study—Arade estuary between the Portimão road bridge and the bar—the most repre-

It was considered that hydrodynamic conditions are determined almost exclusively by the effect of the tide, since the influence of the river flow is very small, given the regularization imposed by the built dam upstream; it was assumed for the river flow the value of 10 m3

Upstream of the model limit, the roman bridge of Silves, the volume of the tide prism is very small, due to both the small widths of the channels of the water lines and the high levels of

For the hydrodynamic modeling, the RMA2 model, with the SMS interface, was used. The mesh of finite elements used for the reference situation is presented in **Figures 2** and **3**. For the future layout, the mesh and the boundary conditions were modified considering the future hydrography, according to what each work planned, the respective geometry and the limit

To calibrate the model in the reference situation, three points were taken into account, respectively, upstream of the railway bridge in Mexilhoeira Grande, at the junction of the Odelouca River with the Arade River, and downstream of the Roman Bridge in Silves, as referenced in **Figure 4**. The observations available for the calibration of the model, considering the free surface of the flow, took place during a tide cycle. Besides the points used for the calibration of the model, **Figure 4** shows the points used for the overall analysis of the results and also

The variables obtained in the calibration of the model were used in the future layout model,

with minor adjustments to eliminate instabilities of convergence of the iterations.

/s.

37

sentative situation possible.

the bottoms.

of analysis.

for the detailed analyses.

In the reference situation for the case study, the identification was made using tools of geographic information systems, namely, 3D Analyst and ArcGIS Spatial Analyst. The zoning of the estuary area according to the grain size of the sediments was then established.

#### **2.3. Hydrodynamics**

According to the applied methodology, the determination of the maximum velocities of the ebb tide in each of the study zones must be performed, for the reference situation. Later, the determination of the maximum velocities of ebb tide, for the new layout, must also be carried out.

#### **2.4. Sedimentation and erosion (M5)**

The following step of the stated method is comprised by the identification of the areas where sedimentation and erosion occur and also where a balance between both states takes place, using the different digital terrain modules obtained from bathymetry in different years.

For each study area, the maximum velocities of the ebb tide are related with the erosion or sedimentation status verified.

#### **2.5. Simulation for layout changes**

By the integration of the gathered results from the reference situation and the new layout, it is aimed in this stage to foresee the changes in erosion and sedimentation patterns, comparing the flow changes in both situations. So, the areas in which erosion and sedimentation are likely to increase, or to maintain a probable balance, are then identified, estimating the variation in yearly volume dredging.

Finally, according to the results, an eventual consideration of alternative solutions to dredging can be studied.

### **3. Case study: harbor of Portimão**

In this chapter, the hydrodynamics of the Arade estuary is analyzed considering the area of port interest (Port of Portimão), studying the present situation of deposition and erosion of sediments, relating them, based on the detailed information about the model [8].

The port of Portimão presents the best natural conditions on the southern coast of Portugal. The area under port jurisdiction runs from the mouth of the River Arade to the Roman bridge in Silves, 13 km upstream. At present, the port area only encompasses the frontier stretch of the city of Portimão, and it can be seen that, upstream of the first Arade Bridge, the river can only be used by small tourist boats and in certain places only at high tide. Two breakwaters protect the entrance to the port, with a minimum of 200 m wide, followed by a 150 m wide navigation channel, which extends to the commercial wharf and the fishing port [9]. The W and E quays have lengths of 820 m and 680 m, respectively. In the wide front, there is a circular and maneuvering basin. On the right bank, from the inlet upstream, first there is Portimão Marina; then the Navy Pier, with a length of about 200 m; and the Terminal of Passengers and General Cargo, about 340 m long; further upstream, in a lower depth zone, there are other docks and berths for recreational craft. The fishing port is located on the left bank, with mooring wharves, a shipyard and a supply pier. The port of Portimão is used for trade, cruising, fishing and recreation. There is a weekly ferry link to Madeira and the Canary Islands.

**2.2. Zoning (M4)**

36 Sedimentation Engineering

**2.3. Hydrodynamics**

carried out.

erosion and deposition of materials.

**2.4. Sedimentation and erosion (M5)**

sedimentation status verified.

**2.5. Simulation for layout changes**

tion in yearly volume dredging.

**3. Case study: harbor of Portimão**

ing can be studied.

Following the physicochemical characterization and analysis of the sediments and taking into account the obtained results, the proposed methodology aims the identification of areas of

In the reference situation for the case study, the identification was made using tools of geographic information systems, namely, 3D Analyst and ArcGIS Spatial Analyst. The zoning of

According to the applied methodology, the determination of the maximum velocities of the ebb tide in each of the study zones must be performed, for the reference situation. Later, the determination of the maximum velocities of ebb tide, for the new layout, must also be

The following step of the stated method is comprised by the identification of the areas where sedimentation and erosion occur and also where a balance between both states takes place, using the different digital terrain modules obtained from bathymetry in different years.

For each study area, the maximum velocities of the ebb tide are related with the erosion or

By the integration of the gathered results from the reference situation and the new layout, it is aimed in this stage to foresee the changes in erosion and sedimentation patterns, comparing the flow changes in both situations. So, the areas in which erosion and sedimentation are likely to increase, or to maintain a probable balance, are then identified, estimating the varia-

Finally, according to the results, an eventual consideration of alternative solutions to dredg-

In this chapter, the hydrodynamics of the Arade estuary is analyzed considering the area of port interest (Port of Portimão), studying the present situation of deposition and erosion of

The port of Portimão presents the best natural conditions on the southern coast of Portugal. The area under port jurisdiction runs from the mouth of the River Arade to the Roman bridge

sediments, relating them, based on the detailed information about the model [8].

the estuary area according to the grain size of the sediments was then established.

The modeling of the estuary of the River Arade includes the west coastal zone up to Ponta da Piedade, west of Lagos and the east coastal zone till near Vilamoura. Given the referred coast extension, it was intended to ensure that the tide conditions that were taken into account at the entrance of the bar would be free of undesired influences from the boundary conditions.

Regarding the study area towards the inland, the river Arade was considered as far as the Roman bridge of Silves, in an extension of 13 km, and the Odelouca stream to a section about 14 km upstream from the mouth of the Arade. This way, it was intended to obtain, in the area under study—Arade estuary between the Portimão road bridge and the bar—the most representative situation possible.

It was considered that hydrodynamic conditions are determined almost exclusively by the effect of the tide, since the influence of the river flow is very small, given the regularization imposed by the built dam upstream; it was assumed for the river flow the value of 10 m3 /s. Upstream of the model limit, the roman bridge of Silves, the volume of the tide prism is very small, due to both the small widths of the channels of the water lines and the high levels of the bottoms.

For the hydrodynamic modeling, the RMA2 model, with the SMS interface, was used. The mesh of finite elements used for the reference situation is presented in **Figures 2** and **3**. For the future layout, the mesh and the boundary conditions were modified considering the future hydrography, according to what each work planned, the respective geometry and the limit of analysis.

To calibrate the model in the reference situation, three points were taken into account, respectively, upstream of the railway bridge in Mexilhoeira Grande, at the junction of the Odelouca River with the Arade River, and downstream of the Roman Bridge in Silves, as referenced in **Figure 4**. The observations available for the calibration of the model, considering the free surface of the flow, took place during a tide cycle. Besides the points used for the calibration of the model, **Figure 4** shows the points used for the overall analysis of the results and also for the detailed analyses.

The variables obtained in the calibration of the model were used in the future layout model, with minor adjustments to eliminate instabilities of convergence of the iterations.

**Figure 2.** Finite element mesh of the case study and the harbor location.

**Figure 3.** Details of the mesh in the estuary of the Arade River: the estuary and the zone that comprises the Dock of San Francisco, the fishing port, the commercial wharf and the Navy Pier and the maneuvering basin.

In **Figure 5**, the topo-hydrography regarded in the hydrodynamic analysis is presented in a very schematic way, and it was based on the surveys carried out in 2003. For the future layout simulation, this hydrography was modified according to the various reviewed works. This way, the velocity and the water heights at each point were obtained. The interventions planned for the port will not have a significant influence on the hydrodynamics upstream the

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 39

**Figure 5.** (a) Topo-hydrography considered for the reference situation and (b) detail of the estuary.

Portimão road bridge, as there will be no changes in that reach.

**Figure 4.** Calibration points and observation points, for comparison of results.

The flow rate considered for both situations (reference situation and future layout) was 5 m3 /s in the Arade River and 5 m3 /s in the Odelouca stream. In fact, the average current flow rate at the Portimão road bridge is estimated at about 10 m3 /s. For the calibration, and taking into account the flow rates verified on the day of the field readings, a flow rate of 0.5 m3 /s was used for each of the streams.

**Figure 4.** Calibration points and observation points, for comparison of results.

**Figure 5.** (a) Topo-hydrography considered for the reference situation and (b) detail of the estuary.

The flow rate considered for both situations (reference situation and future layout) was 5 m3

**Figure 3.** Details of the mesh in the estuary of the Arade River: the estuary and the zone that comprises the Dock of San

account the flow rates verified on the day of the field readings, a flow rate of 0.5 m3

Francisco, the fishing port, the commercial wharf and the Navy Pier and the maneuvering basin.

/s in the Odelouca stream. In fact, the average current flow rate

/s. For the calibration, and taking into

in the Arade River and 5 m3

for each of the streams.

at the Portimão road bridge is estimated at about 10 m3

**Figure 2.** Finite element mesh of the case study and the harbor location.

38 Sedimentation Engineering

/s

/s was used

In **Figure 5**, the topo-hydrography regarded in the hydrodynamic analysis is presented in a very schematic way, and it was based on the surveys carried out in 2003. For the future layout simulation, this hydrography was modified according to the various reviewed works. This way, the velocity and the water heights at each point were obtained. The interventions planned for the port will not have a significant influence on the hydrodynamics upstream the Portimão road bridge, as there will be no changes in that reach.

• Upstream, between the road bridge and the downstream part of the maneuvering basin, as

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 41

• Downstream of the former and to the southern end of the Portimão Marina, as an area of

It is considered that the occurrence of erosion and sedimentation in the mooring area, and the coarser sediments, is more related to the swell of SW, than to the currents caused by

In this zoning, "fine sediments" include materials ranging from fine sand to mud, including silts; in "medium sediments" fine to medium sand, with some silt, are included; the "coarse

**Figure 7** shows the proposed zoning for sediments, which will serve as a basis for the subse-

• To the south of the previous one, and to the bar, as a zone of coarse sediments

quent analysis of the possible acceleration of erosion or sedimentation trends.

**Figure 7.** (a) Sampling points and grain size distribution; (b) simplified zoning of the estuary.

a zone of fine sediments

sediments" include coarse to medium sand.

medium sediments

the tide.

**Figure 6.** Materials (different roughness) considered in the analysis, in the section between the road bridge and immediately downstream of the bar.

Consequently, the "overall" analysis of the results to be achieved will focus only on the section between the Portimão road bridge and the inlet, and so four areas were analyzed in detail: commercial quay and maneuvering basin, Ferragudo channel and Ferragudo bank, the first section of the navigation channel and the inlet. Some considerations are also done about the sandbank channel, upstream the commercial quay. Several zones were considered in the modeling, corresponding to different "materials" and their corresponding roughness, in the RMA2 model, which are represented in **Figure 6**. In fact, the hydrodynamic conditions within the several docks are substantially different from those observed, for example, along the navigation channel.

### **3.1. Zoning (M4)**

Considering the sampling and grain size analysis performed, and considering the fine alternations of thinner and coarser sediments, typical in this type of environment, as well as the various strata, it was decided to divide the estuary into three zones (**Figure 7**):

It is considered that the occurrence of erosion and sedimentation in the mooring area, and the coarser sediments, is more related to the swell of SW, than to the currents caused by the tide.

In this zoning, "fine sediments" include materials ranging from fine sand to mud, including silts; in "medium sediments" fine to medium sand, with some silt, are included; the "coarse sediments" include coarse to medium sand.

**Figure 7** shows the proposed zoning for sediments, which will serve as a basis for the subsequent analysis of the possible acceleration of erosion or sedimentation trends.

**Figure 7.** (a) Sampling points and grain size distribution; (b) simplified zoning of the estuary.

Consequently, the "overall" analysis of the results to be achieved will focus only on the section between the Portimão road bridge and the inlet, and so four areas were analyzed in detail: commercial quay and maneuvering basin, Ferragudo channel and Ferragudo bank, the first section of the navigation channel and the inlet. Some considerations are also done about the sandbank channel, upstream the commercial quay. Several zones were considered in the modeling, corresponding to different "materials" and their corresponding roughness, in the RMA2 model, which are represented in **Figure 6**. In fact, the hydrodynamic conditions within the several docks are substantially different from those observed, for example, along the navigation channel.

**Figure 6.** Materials (different roughness) considered in the analysis, in the section between the road bridge and

Considering the sampling and grain size analysis performed, and considering the fine alternations of thinner and coarser sediments, typical in this type of environment, as well as the

various strata, it was decided to divide the estuary into three zones (**Figure 7**):

**3.1. Zoning (M4)**

immediately downstream of the bar.

40 Sedimentation Engineering

### **3.2. Hydrodynamics**

The reference situation corresponds to the current situation of the port of Portimão, as in 2010; however, the hydrography of the survey of 2003 was used since it is still representative.

For performed modeling, and for all subsequent modeling, the tide of 27 February 2002 (**Figure 8**) was considered for representing a tidal wave, as it corresponds to the obtention of the field values for the calibration of the model. The tide used has a flood level of 3.69 m ZH and a low sea level of 0.30 m ZH.

All the modeling was carried out for a period of 65 hours, i.e. more than five complete cycles of flood and ebb tide. In this way, the aim was to stabilize the obtained results, since, in general, and in the application of the RMA2 model, the two or three first cycles show variations before reaching stabilization. The period considered for analysis, both in this modeling and in the following models, was the between 48 and 62.3 hours of simulation.

**Figures 9**–**11** show some of the results that are considered more relevant for the reference situation. As expected, in this case, there is a delay of almost 1 hour between the peak velocity in the bar and the channel in front of the central zone of Portimão, near the sandbank. There is also a substantial reduction in flow velocity in front of the S. Francisco dock, due to the widening of the flow channel due to the entrance to the fishing port, the S. Francisco dock, and the maneuvering basin. There is also a significant reduction in velocity on the initial section of the channel and in the mooring area, due to the widening of the flow section in that area.

**Figure 8.** Tide used in the modeling, including the 27th of February (calibration data) and the period used in the analysis.

**3.3. Sedimentation and erosion**

the bar and in the channel near the sandbank.

The determination of the areas currently subject to sediment deposition or erosion was done following the methodology explained in Section 2, using the 3D Analyst and the Spatial Analyst tools of ESRI geographic information software. The 2000 and 2003 surveys of the

**Figure 10.** Reference situation. Flow at (a) 53 and (b) 54 hours; (c) delay between the peak of velocity in the ebb tide in

**Figure 9.** Reference situation. Results obtained during ebb flow: (a) 50, (b) 51, (c) 53 and (d) 55 hours.

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 43

**Figure 9.** Reference situation. Results obtained during ebb flow: (a) 50, (b) 51, (c) 53 and (d) 55 hours.

**Figure 10.** Reference situation. Flow at (a) 53 and (b) 54 hours; (c) delay between the peak of velocity in the ebb tide in the bar and in the channel near the sandbank.

#### **3.3. Sedimentation and erosion**

**3.2. Hydrodynamics**

42 Sedimentation Engineering

in that area.

and a low sea level of 0.30 m ZH.

The reference situation corresponds to the current situation of the port of Portimão, as in 2010; however, the hydrography of the survey of 2003 was used since it is still representative.

For performed modeling, and for all subsequent modeling, the tide of 27 February 2002 (**Figure 8**) was considered for representing a tidal wave, as it corresponds to the obtention of the field values for the calibration of the model. The tide used has a flood level of 3.69 m ZH

All the modeling was carried out for a period of 65 hours, i.e. more than five complete cycles of flood and ebb tide. In this way, the aim was to stabilize the obtained results, since, in general, and in the application of the RMA2 model, the two or three first cycles show variations before reaching stabilization. The period considered for analysis, both in this modeling and in

**Figures 9**–**11** show some of the results that are considered more relevant for the reference situation. As expected, in this case, there is a delay of almost 1 hour between the peak velocity in the bar and the channel in front of the central zone of Portimão, near the sandbank. There is also a substantial reduction in flow velocity in front of the S. Francisco dock, due to the widening of the flow channel due to the entrance to the fishing port, the S. Francisco dock, and the maneuvering basin. There is also a significant reduction in velocity on the initial section of the channel and in the mooring area, due to the widening of the flow section

**Figure 8.** Tide used in the modeling, including the 27th of February (calibration data) and the period used in the analysis.

the following models, was the between 48 and 62.3 hours of simulation.

The determination of the areas currently subject to sediment deposition or erosion was done following the methodology explained in Section 2, using the 3D Analyst and the Spatial Analyst tools of ESRI geographic information software. The 2000 and 2003 surveys of the

The two situations of erosion and sediment deposition will be analyzed separately.

In particular, eight distinct locations deserve careful consideration, as follows.

that there was practically no sediment erosion or sedimentation.

tant influence.

deposition of sand.

ance in the current situation.

area.

establishment of the referred port infrastructure.

Firstly the areas where erosion occurs (which are presented in **Figure 12b**) will be analyzed.

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 45

Starting in zone 1, which corresponds to the fishing port, it is important to notice that a maintenance dredging was carried out in 2001, since this zone, and especially the port entrance and the area next to the haul ramp of the shipyards, was very much silted. Therefore, erosion did really not occur here but rather maintenance dredging. In the remaining areas of this fishing port, the alternation between eroded and silted areas, always of very small values, corresponds to the mooring area of the boats, and to the areas under the piers, and indicates

The zone 2, which appears in this analysis as strongly eroded, was in fact subject to a local dredging, so, contrary to the obtained results, this is a zone of strong deposition of sediments; on the other hand, the section upstream of this zone, also at the mouth of the Ferragudo River, is, in fact, an area of high erosion. This is, moreover, an area which is important to analyze with particular attention, since it is probable that the planned works will have there an impor-

In zone 3, the regional departments of environment undertook beach nourishment activities, by placing sands as a coastal reinforcement. According to the empirical experience, confirmed in the present case, the sand that was deposited in this beach was dragged to the mooring area by the effect of the SW waves, so, throughout the tidal range in this zone, there was an erosion of all the material deposited there. Above the level of variation of the tide, there was

Zone 4 corresponds to São Francisco Dock. In this zone, in the period between the two general surveys, the works of establishment of the referred dock were concluded. Thus, there was no erosion here—it is likely that relatively high silting will occur—but rather a dredging for the

The section upstream of the San Francisco Dock and the fishing port and downstream from the road bridge defines the zone 5. Within this area, the erosion is very small, and there is also a small sedimentation under the quay bridges and at the downstream end of the sandbank.

Zone 6 is a muddy, sandy-muddy zone, with a general elevation between low tide and full tide, and is thus under water and out of water in all tide cycles. This zone toggles between erosion and deposition of sediments but always with a very low value, being almost in bal-

Zone 7 is usually a zone of erosion, a tendency that was increased after the construction of the Marina of Portimão, on the right bank of the Arade River, with the consequent narrowing of the channel. The sediments eroded in this Zone will generally be deposited in the mooring

Zone 8 corresponds to the inlet, and the erosion observed there, of the order of 10 cm, is not significant and may be linked to periodic phenomena of storms and, consequently, higher

flow speeds in the inlet. It can be considered that this area is almost in equilibrium.

**Figure 11.** Reference situation. Results obtained during flood flow: (a) 58, (b) 59, (c) 60 and (d) 61 hours.

entire port of Portimão were used. These two surveys allow a good understanding of the erosion sedimentation procedure, as there were no full dredging works in the meantime, only local dredging works.

The application of this model, simple to apply on geo-referenced surveys, allows to determine the locations where the depth has lowered (deposition of material), or risen (erosion of sediments), and to assess the value of these variations, by analyzing the difference on the assessed depths of two hydrographic surveys separated by a certain time interval.

With the application of 3D Analyst and Spatial Analyst to the two surveys of 2000 and 2003, the results, represented graphically in **Figure 12**, were obtained.

**Figure 12.** Results of the application of modules M1 to M5 to the surveys of 2000 and 2003: (a) overall results, (b) erosion and (c) sedimentation areas.

The two situations of erosion and sediment deposition will be analyzed separately.

Firstly the areas where erosion occurs (which are presented in **Figure 12b**) will be analyzed. In particular, eight distinct locations deserve careful consideration, as follows.

Starting in zone 1, which corresponds to the fishing port, it is important to notice that a maintenance dredging was carried out in 2001, since this zone, and especially the port entrance and the area next to the haul ramp of the shipyards, was very much silted. Therefore, erosion did really not occur here but rather maintenance dredging. In the remaining areas of this fishing port, the alternation between eroded and silted areas, always of very small values, corresponds to the mooring area of the boats, and to the areas under the piers, and indicates that there was practically no sediment erosion or sedimentation.

The zone 2, which appears in this analysis as strongly eroded, was in fact subject to a local dredging, so, contrary to the obtained results, this is a zone of strong deposition of sediments; on the other hand, the section upstream of this zone, also at the mouth of the Ferragudo River, is, in fact, an area of high erosion. This is, moreover, an area which is important to analyze with particular attention, since it is probable that the planned works will have there an important influence.

entire port of Portimão were used. These two surveys allow a good understanding of the erosion sedimentation procedure, as there were no full dredging works in the meantime, only

**Figure 11.** Reference situation. Results obtained during flood flow: (a) 58, (b) 59, (c) 60 and (d) 61 hours.

The application of this model, simple to apply on geo-referenced surveys, allows to determine the locations where the depth has lowered (deposition of material), or risen (erosion of sediments), and to assess the value of these variations, by analyzing the difference on the assessed

With the application of 3D Analyst and Spatial Analyst to the two surveys of 2000 and 2003,

**Figure 12.** Results of the application of modules M1 to M5 to the surveys of 2000 and 2003: (a) overall results, (b) erosion

depths of two hydrographic surveys separated by a certain time interval.

the results, represented graphically in **Figure 12**, were obtained.

local dredging works.

44 Sedimentation Engineering

and (c) sedimentation areas.

In zone 3, the regional departments of environment undertook beach nourishment activities, by placing sands as a coastal reinforcement. According to the empirical experience, confirmed in the present case, the sand that was deposited in this beach was dragged to the mooring area by the effect of the SW waves, so, throughout the tidal range in this zone, there was an erosion of all the material deposited there. Above the level of variation of the tide, there was deposition of sand.

Zone 4 corresponds to São Francisco Dock. In this zone, in the period between the two general surveys, the works of establishment of the referred dock were concluded. Thus, there was no erosion here—it is likely that relatively high silting will occur—but rather a dredging for the establishment of the referred port infrastructure.

The section upstream of the San Francisco Dock and the fishing port and downstream from the road bridge defines the zone 5. Within this area, the erosion is very small, and there is also a small sedimentation under the quay bridges and at the downstream end of the sandbank.

Zone 6 is a muddy, sandy-muddy zone, with a general elevation between low tide and full tide, and is thus under water and out of water in all tide cycles. This zone toggles between erosion and deposition of sediments but always with a very low value, being almost in balance in the current situation.

Zone 7 is usually a zone of erosion, a tendency that was increased after the construction of the Marina of Portimão, on the right bank of the Arade River, with the consequent narrowing of the channel. The sediments eroded in this Zone will generally be deposited in the mooring area.

Zone 8 corresponds to the inlet, and the erosion observed there, of the order of 10 cm, is not significant and may be linked to periodic phenomena of storms and, consequently, higher flow speeds in the inlet. It can be considered that this area is almost in equilibrium.

Regarding some of the areas where apparently sedimentation occurs, such as the fishing port, the sediment deposition trend has already been discussed above and related to the observed erosions.

As for the four areas where sedimentation occurs, referred as zones A–D and referenced in **Figure 12c**, these have the greatest interest for port management.

Zone A corresponds to the downstream end of the existing sandbank in front of the central zone of Portimão and is located where the channel widens, with consequent slowing of the flow velocity which results in a reduction of the capacity of solid transport of the river. One of the planned works in the new layout is the dredging of the referred sandbank. There will be an increase of the tide prism, but as the flow section increases, it is not sure if the flow velocity will decrease; as it is possible that there will be a reduction in erosion in the area of the current sandbank, it is important to analyze this area regarding the eventual hydrodynamic change. So, a careful analysis of foreseeable speed variations will be carried out.

Zone B, corresponding to the commercial wharf and the maneuvering basin, is the widest zone in this section of the estuary, where, therefore, the flow velocities decrease, as well as the transportation capacity of the flow, with significant rate of sedimentation.

Zone C is a particularly sensitive zone. In fact, the alternation of the erosion and deposition zones, which are always of small thickness, suggests that the system is close to equilibrium in the navigation channel within this Zone. However, there is a marked deposition both at the entrance to Portimão's marina, on the right bank, and along the left bank of sand, which will be dredged to carry out the planned arrangement of the Ferragudo marginal. Thus, the width of the channel in this section will increase, and it is necessary to carefully analyze what will happen with the flow velocities, especially in the area of the navigation channel.

The zone D, corresponding to the first section of the navigation channel, and the mooring area, is subject to heavy siltation since it is the widest area of the estuary, and that is downstream of areas of substantial erosion, namely, zones 3 and 7.

The histogram (**Figure 13**) shows the distribution of erosion and sedimentation from 2000 to 2003, using ArcGis Space Analyst. Almost all of the values are between −1 m (erosion) and +1 m (sedimentation). Values outside this range correspond, in fact, to one-off dredging interventions or landfill works. Even in the −1 to +1 m interval, part of the values was caused either by dredging or by land filling.

A more detailed analysis of the results is shown in **Figures 14** and **15**. **Figure 14** presents the same results of **Figure 15b** and **c** but superimposed on the hydrography of 2003.

The direct comparison of the two situations, on the section of the navigation channel between the commercial dock and the Marina de Portimão, shows a mixing of the deposition and sedimentation areas. Considering **Figure 14**, where the section in reference is presented in more detail, both the erosions and the settlements have an absolute value inferior to 0.5 m throughout the zone. The analysis of the right-hand side of this same figure suggests that, in general, this absolute value for erosions and sedimentation is, in fact, less than 0.20 m. It also suggests that an interchange occurs at short distance (distances of the order of the metre) between erosion and sedimentation, with the exception of the river bank areas, where, in fact,

only sedimentation is observed, with a value between 0.20 and 0.50 m. Thus in this section of the channel, a relative stability is observed, and the described sedimentation and erosion pattern is due to sediment drift in the bottom of the canal, caused by the tide, as well as the

**Figure 14.** (a) Sedimentation areas on the 2003 hydrography and (b) Erosion.

**Figure 13.** Distribution histogram for the thickness of erosion and sedimentation.

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 47

propellers of the vessels.

**Figure 13.** Distribution histogram for the thickness of erosion and sedimentation.

Regarding some of the areas where apparently sedimentation occurs, such as the fishing port, the sediment deposition trend has already been discussed above and related to the observed

As for the four areas where sedimentation occurs, referred as zones A–D and referenced in

Zone A corresponds to the downstream end of the existing sandbank in front of the central zone of Portimão and is located where the channel widens, with consequent slowing of the flow velocity which results in a reduction of the capacity of solid transport of the river. One of the planned works in the new layout is the dredging of the referred sandbank. There will be an increase of the tide prism, but as the flow section increases, it is not sure if the flow velocity will decrease; as it is possible that there will be a reduction in erosion in the area of the current sandbank, it is important to analyze this area regarding the eventual hydrodynamic change.

Zone B, corresponding to the commercial wharf and the maneuvering basin, is the widest zone in this section of the estuary, where, therefore, the flow velocities decrease, as well as the

Zone C is a particularly sensitive zone. In fact, the alternation of the erosion and deposition zones, which are always of small thickness, suggests that the system is close to equilibrium in the navigation channel within this Zone. However, there is a marked deposition both at the entrance to Portimão's marina, on the right bank, and along the left bank of sand, which will be dredged to carry out the planned arrangement of the Ferragudo marginal. Thus, the width of the channel in this section will increase, and it is necessary to carefully analyze what will

The zone D, corresponding to the first section of the navigation channel, and the mooring area, is subject to heavy siltation since it is the widest area of the estuary, and that is down-

The histogram (**Figure 13**) shows the distribution of erosion and sedimentation from 2000 to 2003, using ArcGis Space Analyst. Almost all of the values are between −1 m (erosion) and +1 m (sedimentation). Values outside this range correspond, in fact, to one-off dredging interventions or landfill works. Even in the −1 to +1 m interval, part of the values was caused either

A more detailed analysis of the results is shown in **Figures 14** and **15**. **Figure 14** presents the

The direct comparison of the two situations, on the section of the navigation channel between the commercial dock and the Marina de Portimão, shows a mixing of the deposition and sedimentation areas. Considering **Figure 14**, where the section in reference is presented in more detail, both the erosions and the settlements have an absolute value inferior to 0.5 m throughout the zone. The analysis of the right-hand side of this same figure suggests that, in general, this absolute value for erosions and sedimentation is, in fact, less than 0.20 m. It also suggests that an interchange occurs at short distance (distances of the order of the metre) between erosion and sedimentation, with the exception of the river bank areas, where, in fact,

same results of **Figure 15b** and **c** but superimposed on the hydrography of 2003.

**Figure 12c**, these have the greatest interest for port management.

So, a careful analysis of foreseeable speed variations will be carried out.

transportation capacity of the flow, with significant rate of sedimentation.

happen with the flow velocities, especially in the area of the navigation channel.

stream of areas of substantial erosion, namely, zones 3 and 7.

by dredging or by land filling.

erosions.

46 Sedimentation Engineering

**Figure 14.** (a) Sedimentation areas on the 2003 hydrography and (b) Erosion.

only sedimentation is observed, with a value between 0.20 and 0.50 m. Thus in this section of the channel, a relative stability is observed, and the described sedimentation and erosion pattern is due to sediment drift in the bottom of the canal, caused by the tide, as well as the propellers of the vessels.

includes a new marina, the reshaping of the river bank downstream Ferragudo and the deep-

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 49

Regarding the sandbank area, a dredging level of −1 m ZH was considered. However this value is not yet final. In the analysis of the obtained results, it will be discussed which would be the most advantageous level for dredging, from the hydrodynamic point of view. **Figures 16**–**18**

**Figure 16.** Modeling with the new layout. Results for ebb tide: (a) 50, (b) 51, (c) 53 and (d) 55 hours (see **Figure 12**).

**Figure 17.** Modeling with the new layout. The delay of the peak velocity in ebb tide (c), between the harbor inlet and the

sandbank (a) 53 and (b) 54 hours.

ening of the navigation channel in order to allow larger ships.

present some relevant results obtained for the whole harbor.

**Figure 15.** (a) Total erosions and sedimentations, 1 m intervals, (b) erosions from 0 to −0.5 m and sedimentations from 0 to +0.5 m, (c) erosions from 0 to −0.20 m and sedimentations from 0 to +0.20 m.

Another area that deserves a careful analysis is the one that constitutes the section, limited upstream by the road bridge and downstream by the south end of the maneuvering basin. The observation of **Figure 14** shows that there is a high erosion rate in the channel, but not in the sandbank, probably due to the small channel width between the shallows in front of the shipyards and the central zone of Portimão, where higher flow speeds are verified.

Downstream, with the widening of the flow section, the velocities decrease, and a strong sedimentation of 0.50 m in the canal and in the maneuver basin is observed. That is to say, the sandbank is moving downstream, which is a serious problem for the management of the port. It is necessary to consider the complete removal of this sandbank or at least a dredging intervention that would establish a balance, without sedimentation or erosion, in the sandbank section.

As can be seen from **Figure 15**, in the navigation channel and the anchoring area at the southern end of the estuary, most of the erosions and sedimentations are of the order of 0.20 m; however, in some localized areas, higher values are observed. But in the navigation channel, throughout this section, the sedimentation is always on the order of 0.50 m.

In the bar itself, erosions reach, for this same period of 3 years, values of 0.50 m.

#### **3.4. Simulation for layout changes**

After the calibration of the model for the reference situation, it was applied to the new layout, changing accordingly the topography and hydrography of the harbor. The new layout includes a new marina, the reshaping of the river bank downstream Ferragudo and the deepening of the navigation channel in order to allow larger ships.

Regarding the sandbank area, a dredging level of −1 m ZH was considered. However this value is not yet final. In the analysis of the obtained results, it will be discussed which would be the most advantageous level for dredging, from the hydrodynamic point of view. **Figures 16**–**18** present some relevant results obtained for the whole harbor.

**Figure 16.** Modeling with the new layout. Results for ebb tide: (a) 50, (b) 51, (c) 53 and (d) 55 hours (see **Figure 12**).

Another area that deserves a careful analysis is the one that constitutes the section, limited upstream by the road bridge and downstream by the south end of the maneuvering basin. The observation of **Figure 14** shows that there is a high erosion rate in the channel, but not in the sandbank, probably due to the small channel width between the shallows in front of the

**Figure 15.** (a) Total erosions and sedimentations, 1 m intervals, (b) erosions from 0 to −0.5 m and sedimentations from 0

Downstream, with the widening of the flow section, the velocities decrease, and a strong sedimentation of 0.50 m in the canal and in the maneuver basin is observed. That is to say, the sandbank is moving downstream, which is a serious problem for the management of the port. It is necessary to consider the complete removal of this sandbank or at least a dredging intervention that would establish a balance, without sedimentation or erosion, in the sand-

As can be seen from **Figure 15**, in the navigation channel and the anchoring area at the southern end of the estuary, most of the erosions and sedimentations are of the order of 0.20 m; however, in some localized areas, higher values are observed. But in the navigation channel,

After the calibration of the model for the reference situation, it was applied to the new layout, changing accordingly the topography and hydrography of the harbor. The new layout

shipyards and the central zone of Portimão, where higher flow speeds are verified.

to +0.5 m, (c) erosions from 0 to −0.20 m and sedimentations from 0 to +0.20 m.

throughout this section, the sedimentation is always on the order of 0.50 m.

In the bar itself, erosions reach, for this same period of 3 years, values of 0.50 m.

bank section.

48 Sedimentation Engineering

**3.4. Simulation for layout changes**

**Figure 17.** Modeling with the new layout. The delay of the peak velocity in ebb tide (c), between the harbor inlet and the sandbank (a) 53 and (b) 54 hours.

effect in the main part of the estuary, and so the referred influences were not considered in this analysis. However, taking into account the new layout, **Figure 19**, it can be observed that the construction of the new marina affects the main flow in the channel leading it to the right

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 51

The new shape for the Ferragudo river bank will increase the flow velocity near the left margin. Also the flow, as being diverted by the promontory of the castle of S. João towards the right bank, will increase the velocity near the entrance of the Marina of Portimão; moreover, there is an flow velocity increase, upstream of the São Francisco dock, in the area of the sandbank, due to its dredging to −1 m. The planned dredging will have a significant influence on the flow in the sandbank area, where the flow will be more evenly distributed over the whole width, with a significant reduction of the maximum speed that occurred in the reference situ-

In front of the commercial wharf, and the new marina, is located the maneuvering basin of the harbor; as a consequence of the increase in the ships draft that is aimed, and also due to the construction of the new marina, this area will be dredged, and so it will present a larger water section. As it can be seen from the velocity variation from the reference situation, there will be

As for the maneuvering basin, **Figure 21**, there is also a clear reduction of the velocity; the peak velocity values obtained for the ebb tide were 0.076 m/s and for the flood tide 0.063 m/s.

**Figure 20.** Upstream of the study area, in the sandbank in front of the town, the dredging of that sandbank will reduce

bank, downstream of the commercial wharf.

ation in the channel near the right bank of the river (**Figure 20**).

a still significant decrease in the velocity in this area.

significantly the velocities (velocity in absolute value).

**Figure 18.** Modeling with the new layout. Results for the flood tide: (a) 58, (b) 59, (c) 60 and (d) 61 hours.

### **4. Results**

According to the mineralogy and grain size of sediments, the longshore transport of sediments only affects this estuary near the inlet, more precisely in the mooring area, due to SW waves. In this particular case study, the longshore transport and the waves have no significant

**Figure 19.** The estuary, in the peak of ebb tide (53 hours), (a) for the reference situation and (b) for the new layout simulation.

effect in the main part of the estuary, and so the referred influences were not considered in this analysis. However, taking into account the new layout, **Figure 19**, it can be observed that the construction of the new marina affects the main flow in the channel leading it to the right bank, downstream of the commercial wharf.

The new shape for the Ferragudo river bank will increase the flow velocity near the left margin. Also the flow, as being diverted by the promontory of the castle of S. João towards the right bank, will increase the velocity near the entrance of the Marina of Portimão; moreover, there is an flow velocity increase, upstream of the São Francisco dock, in the area of the sandbank, due to its dredging to −1 m. The planned dredging will have a significant influence on the flow in the sandbank area, where the flow will be more evenly distributed over the whole width, with a significant reduction of the maximum speed that occurred in the reference situation in the channel near the right bank of the river (**Figure 20**).

In front of the commercial wharf, and the new marina, is located the maneuvering basin of the harbor; as a consequence of the increase in the ships draft that is aimed, and also due to the construction of the new marina, this area will be dredged, and so it will present a larger water section. As it can be seen from the velocity variation from the reference situation, there will be a still significant decrease in the velocity in this area.

**4. Results**

50 Sedimentation Engineering

simulation.

According to the mineralogy and grain size of sediments, the longshore transport of sediments only affects this estuary near the inlet, more precisely in the mooring area, due to SW waves. In this particular case study, the longshore transport and the waves have no significant

**Figure 18.** Modeling with the new layout. Results for the flood tide: (a) 58, (b) 59, (c) 60 and (d) 61 hours.

**Figure 19.** The estuary, in the peak of ebb tide (53 hours), (a) for the reference situation and (b) for the new layout

As for the maneuvering basin, **Figure 21**, there is also a clear reduction of the velocity; the peak velocity values obtained for the ebb tide were 0.076 m/s and for the flood tide 0.063 m/s.

**Figure 20.** Upstream of the study area, in the sandbank in front of the town, the dredging of that sandbank will reduce significantly the velocities (velocity in absolute value).

**Figure 21.** It can be seen from the velocity variation that there will be a still significant decrease in the velocity in this area (velocity in absolute value) and so an increased sedimentation.

The navigation channel, in front of Ferragudo, **Figure 22**, presents almost no velocity variation from the reference situation to the final layout situation. This is due to contrary effects of the various interventions planned for the harbor: on one hand, the dredging of the channel will increase the section flow and, so, decrease the velocity, and on the other hand, the works upstream, marina, sandbank, by example, will increase the tide prism upstream this analysis point and so increase the velocity. The referred effects, opposite to each other, cause almost

Sedimentation and Erosion in Harbor Estuaries http://dx.doi.org/10.5772/intechopen.74049 53

**Figure 23.** At the inlet the velocity will decrease slightly (velocity in absolute value).

After the planned work completion, the predicted peak velocity of the ebb in the inlet is 0.36 m/s. In the flood, the peak velocity, which in the reference situation was 0.36 m/s, will then change, with the three interventions performed, to 0.32 m/s (**Figure 23**). So, at the inlet the velocity will decrease slightly, and so an increase in sedimentation and consequently of

Reference situation 0.350 0.090 0.220 0.400 New layout 0.220 0.077 0.225 0.365

Notes: Ref. situation erosion zone; Ref. situation limited erosion zone; Ref. situation equilibrium zone; Ref.

**Sandbank Maneuvering Basin Ferragudo Inlet**

no variation in velocity.

dredging should be expected.

situation sedimentation zone.

**Table 1.** Result summary.

**Analyzed situation Ebb maximum velocity (m/s)**

**Figure 22.** In front of Ferragudo, the velocity is almost unchanged (velocity in absolute value).

**Figure 23.** At the inlet the velocity will decrease slightly (velocity in absolute value).

The navigation channel, in front of Ferragudo, **Figure 22**, presents almost no velocity variation from the reference situation to the final layout situation. This is due to contrary effects of the various interventions planned for the harbor: on one hand, the dredging of the channel will increase the section flow and, so, decrease the velocity, and on the other hand, the works upstream, marina, sandbank, by example, will increase the tide prism upstream this analysis point and so increase the velocity. The referred effects, opposite to each other, cause almost no variation in velocity.

After the planned work completion, the predicted peak velocity of the ebb in the inlet is 0.36 m/s. In the flood, the peak velocity, which in the reference situation was 0.36 m/s, will then change, with the three interventions performed, to 0.32 m/s (**Figure 23**). So, at the inlet the velocity will decrease slightly, and so an increase in sedimentation and consequently of dredging should be expected.

**Table 1.** Result summary.

**Figure 22.** In front of Ferragudo, the velocity is almost unchanged (velocity in absolute value).

**Figure 21.** It can be seen from the velocity variation that there will be a still significant decrease in the velocity in this area

(velocity in absolute value) and so an increased sedimentation.

52 Sedimentation Engineering

**Table 1** presents, for the four reference sections above mentioned, the ebb maximum velocity in the reference situation and in the simulation considering the new layout. It presents also, for the reference situation, if each zone presents erosion and sedimentation or is in equilibrium.

**References**

Portugal, 16 p (in Portuguese)

IH, 21 and 22 Jun 2010, Lisbon. pp. 251-254 (in Portuguese)

Lisbon: Direcção-Geral de Portos; 1985 (in Portuguese)

[1] Santos Ferreira AMG, Trigo Teixeira AA. As novas infraestruturas portuárias no estuário do Arade: influência prevista na hidrodinâmica estuarina. In: Proceedings of the 6th Jornadas Portuguesas de Engenharia Costeira e Portuária, 8 and 9 Oct 2009, Funchal,

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[2] Silva APF, Santos-Ferreira A, Dias E. Análise multitemporal e morfodinâmica no estuário do Arade com geoprocessamento automático. In: Proceedings of the 1st Jornadas Hidrográficas,

[3] Trigo Teixeira AA, Santos Ferreira AMG. Erosão e sedimentação no estuário do rade. Interpretação da evolução com consideração da hidrodinâmica estuarina. In: Proceedings of the 1st Jornadas Hidrográficas, IH, 21 and 22 Jun 2010, Lisbon. pp. 255-258 (in Portuguese)

[4] Santos-Ferreira A, Dias E, Trigo Teixeira AA, Silva APF. Análise morfodinâmica por geoprocessamento automático: aplicação ao planeamento de dragagens no porto de Portimão. In: Proceedings 6th Congresso Planeamento e Gestão de Zonas Costeiras de Países de expressão portuguesa, 4-8 Apr 2011, Boavista Island, Cape Verde. 14 p (in Portuguese) [5] Dias E. Utilização de um Sistema de Informação Geográfica na Caracterização de Áreas de Dragagem [thesis]. ISEGI, UNL, Lisboa (Portugal). 2005. 150 p. (in Portuguese)

[6] Santos-Ferreira A, Dias E, Silva APF, Santos C, Cabral M. Dredging of Vila do Conde harbor, Portugal – Contamination of sediments. In: Proceedings 8th International

[7] Santos-Ferreira A, da Silva APF, Dias E. Harbor geotechnics: The case of the Portuguese small Harbor. In: Proceedings of GeoHubei International Conference 2014 – Sustainable Civil Infrastructures: Innovative Technologies and Materials, Yichang, Hubei, China, 20-22 Jul 2014. Application of Nanotechnology in Pavements, Geological Disasters, and Foundation Settlement Control Technology, GSP 244. 2014. pp. 78-85 (© ASCE 2014) [8] Santos Ferreira AMG. Impacte do Plano do Porto de Portimão na Hidrodinâmica do Estuário do Arade [thesis]. IST – University of Lisbon; 2006. 145 p (in Portuguese)

[9] Weinholtz MB. Estudo da Situação do Troço Terminal do Rio Arade a Jusante das Pontes e Zona marítima Frontal após a Conclusão da Primeira Fase das Obras Portuárias.

### **5. Conclusions**

As stated, harbors are, whenever possible, established in estuaries to take advantage of the existing natural safety and protection conditions. But to keep harbors in a safe and usable way, periodic dredging works are carried out. The expansion of harbor's activities and the growth of maritime traffic may lead to changes in the harbor's layout or to improvements of navigation channels and basins depths. Such adjustments entail changes in estuarine hydrodynamics, and therefore the usual dredging rates are subject to alteration, namely, tending to increase. It is then important to assess the influence of a harbor's new layout on the solid transport pattern and how its effects can be minimized, aiming the reduction of economic and environmental impacts. Within this context, in this chapter estuary hydrodynamics and sedimentation-erosion patterns were summarized. Also, the modeling methodology for planning and management of dredging works which uses geo-processing automatic GIS environment, developed by the Portuguese harbor authority, was presented. Finally, the case study of harbor of Portimão was also described showing the implementation of the referred methodology.

The method presented to estimate erosion and deposition ratings, and so allowing to plan dredging works, has proven its usefulness and proved to be of easy implementation. In the case study presented, it allowed to identify the areas where the hydrodynamic changes will likely increase sedimentation and also where no change or an increase of erosion should be expected. Lower velocities will mean higher depositions and, accordingly, a greater volume to dredge. Anyway its application must be careful, as it is important, besides the use of adequate topographic surveys, to know where, in the time period of those topographic surveys, dredging works were carried on, as well as the volumes dredged.

Also the hydrodynamic pattern of the harbor is of the uttermost importance, mainly when a changing in the harbor layout is planned, in order to forecast the changing in the erosion deposition rates in the different harbor zones.

### **Author details**

Alexandre M.G. Santos Ferreira\* and Cláudia S.N. Santos

\*Address all correspondence to<EMAIL_ADDRESS>
DGRM, Directorate-General for Natural Resources, Safety and Maritime Services Lisbon, Portugal

### **References**

**Table 1** presents, for the four reference sections above mentioned, the ebb maximum velocity in the reference situation and in the simulation considering the new layout. It presents also, for the reference situation, if each zone presents erosion and sedimentation or is in equilibrium.

As stated, harbors are, whenever possible, established in estuaries to take advantage of the existing natural safety and protection conditions. But to keep harbors in a safe and usable way, periodic dredging works are carried out. The expansion of harbor's activities and the growth of maritime traffic may lead to changes in the harbor's layout or to improvements of navigation channels and basins depths. Such adjustments entail changes in estuarine hydrodynamics, and therefore the usual dredging rates are subject to alteration, namely, tending to increase. It is then important to assess the influence of a harbor's new layout on the solid transport pattern and how its effects can be minimized, aiming the reduction of economic and environmental impacts. Within this context, in this chapter estuary hydrodynamics and sedimentation-erosion patterns were summarized. Also, the modeling methodology for planning and management of dredging works which uses geo-processing automatic GIS environment, developed by the Portuguese harbor authority, was presented. Finally, the case study of harbor of Portimão was also described showing the implementation of the referred

The method presented to estimate erosion and deposition ratings, and so allowing to plan dredging works, has proven its usefulness and proved to be of easy implementation. In the case study presented, it allowed to identify the areas where the hydrodynamic changes will likely increase sedimentation and also where no change or an increase of erosion should be expected. Lower velocities will mean higher depositions and, accordingly, a greater volume to dredge. Anyway its application must be careful, as it is important, besides the use of adequate topographic surveys, to know where, in the time period of those topographic surveys,

Also the hydrodynamic pattern of the harbor is of the uttermost importance, mainly when a changing in the harbor layout is planned, in order to forecast the changing in the erosion

DGRM, Directorate-General for Natural Resources, Safety and Maritime Services Lisbon,

dredging works were carried on, as well as the volumes dredged.

deposition rates in the different harbor zones.

Alexandre M.G. Santos Ferreira\* and Cláudia S.N. Santos

\*Address all correspondence to<EMAIL_ADDRESS>
**5. Conclusions**

54 Sedimentation Engineering

methodology.

**Author details**

Portugal

**Chapter 4**

Provisional chapter

**Sedimentary Processes and Sedimentation in the**

Sedimentary Processes and Sedimentation in the

Prince Suka Momta

Abstract

Prince Suka Momta

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74135

and shallow marine origin.

1. Introduction

**Shallow Offshore, Eastern Niger Delta, Gulf of Guinea**

The Cretaceous Afikpo sedimentary Basin in Southeastern Nigeria contains rocks of fluvial, deltaic and shallow marine origin. This study examines the role of sedimentary processes in sediment distribution in the various geologic environments. The outcrop sections and the Afikpo River were studied by visual observation and photographing of important features during a field mapping exercise. Well log data from the Niger Delta Basin were also used to infer depositional environments based on gamma ray log motifs. These outcrop sections consist of fluvial, deltaic and shallow marine sediments that occurred as braids, point-bars, mouth-bars and beach/regressive bars. Braids and point-bar deposits also occurred within the recent Afikpo River channel, a major conduit transporting sediments to the offshore area of eastern Niger Delta. Sandstone outcrops showing a mouthbar architecture occurred at Akpoha Town east of Afikpo Town, with a shallow marine sequence at Amasiri area, west of Afikpo Town. The Amasiri sandstone is a massive outcrop with large lateral extent covering more than 8 kilometers. Gamma ray log trends observed on well log from offshore area in the eastern Niger Delta indicated deposits of fluvial, deltaic

Keywords: Afikpo Basin, cross river, fluvial, sedimentation, Niger delta, shallow offshore

The Gulf of Guinea has recently received tremendous attention from both the oil companies and the academia for several decades due to increasing hydrocarbon discoveries in the region. To maximize production from offshore reservoirs, there is the need to properly understand the processes of sedimentation and the consequent depositional architecture of facies and their distribution within the marine realm. The two major rivers (Niger and Benue rivers) in Nigeria

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Shallow Offshore, Eastern Niger Delta, Gulf of Guinea

DOI: 10.5772/intechopen.74135

#### **Sedimentary Processes and Sedimentation in the Shallow Offshore, Eastern Niger Delta, Gulf of Guinea** Sedimentary Processes and Sedimentation in the Shallow Offshore, Eastern Niger Delta, Gulf of Guinea

DOI: 10.5772/intechopen.74135

Prince Suka Momta Prince Suka Momta

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.74135

#### Abstract

The Cretaceous Afikpo sedimentary Basin in Southeastern Nigeria contains rocks of fluvial, deltaic and shallow marine origin. This study examines the role of sedimentary processes in sediment distribution in the various geologic environments. The outcrop sections and the Afikpo River were studied by visual observation and photographing of important features during a field mapping exercise. Well log data from the Niger Delta Basin were also used to infer depositional environments based on gamma ray log motifs. These outcrop sections consist of fluvial, deltaic and shallow marine sediments that occurred as braids, point-bars, mouth-bars and beach/regressive bars. Braids and point-bar deposits also occurred within the recent Afikpo River channel, a major conduit transporting sediments to the offshore area of eastern Niger Delta. Sandstone outcrops showing a mouthbar architecture occurred at Akpoha Town east of Afikpo Town, with a shallow marine sequence at Amasiri area, west of Afikpo Town. The Amasiri sandstone is a massive outcrop with large lateral extent covering more than 8 kilometers. Gamma ray log trends observed on well log from offshore area in the eastern Niger Delta indicated deposits of fluvial, deltaic and shallow marine origin.

Keywords: Afikpo Basin, cross river, fluvial, sedimentation, Niger delta, shallow offshore

### 1. Introduction

The Gulf of Guinea has recently received tremendous attention from both the oil companies and the academia for several decades due to increasing hydrocarbon discoveries in the region. To maximize production from offshore reservoirs, there is the need to properly understand the processes of sedimentation and the consequent depositional architecture of facies and their distribution within the marine realm. The two major rivers (Niger and Benue rivers) in Nigeria

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

are of significance in the distribution of sediments in the east and western offshore area of the country. The Niger River is active and supplies sediments toward the western part of the Niger Delta, whereas, the Benue River concentrates sedimentation in the eastern offshore (Figure 1) area. There are subsurface evidences of the occurrence of ancient river channels and canyons that served as conduits for transporting sediments from the continent to the Gulf of Guinea [1]. These sedimentation processes are still active today and sediments keep building out along the shores and on the continental shelf of the Niger Delta. We will look at the outcrop evidence of fluvial and marine sandstones at Afikpo Town, and trace the course of the Cross River from Afikpo (Figure 2) to the coastal town of Calabar where presently these sediments are deposited into the estuaries and open marine environments. The subsurface occurrence of shallow marine facies will serve as analogue to the outcrop exposures of marine sandstones in the Afikpo basin. The eastern offshore of the Niger Delta occurs within few kilometers away from the active volcanic line of the Cameroun Mountain. The geomorphic features and surface processes in this region are of interest to most researchers and enables the paleo-reconstruction of subsurface sediments of Tortonian age in the offshore area. The adjacent highland areas consisting of the Precambrian basement of the Oban Massif, Obudu Plateau and the Cameroun Mountain form the sources of weathered sediments that are transported through the Great Kwa and Calabar Rivers to the offshore area south of Calabar Town, South Eastern Nigeria [2]. These rocks are weathered, highly fractured, foliated, and exposed by stream channels cutting through them [2]. They from the major provenance of sediments deposited within the shallow to deep offshore through submarine canyons. In this paper, we will consider a major tributary

of the Benue River, the Afikpo-Cross River, which transport sediments from the hinterland in eastern Nigeria to the eastern offshore area of the Niger Delta. We will discuss the continental, deltaic and shallow marine processes, sediments and their responses from both outcrop and subsurface data. A consideration of the subsurface architecture of shallow marine sediments from the eastern part of the Tertiary Niger Delta sedimentary basin will also be made. The study and understanding of sedimentary processes and their responses have serious economic,

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Generally, there are two major rivers in Nigeria that run through the country with several tributaries. They are; the Niger and Benue rivers. The Niger river empties into the Atlantic Ocean in the south- western axis of Nigeria, whereas the Benue River in the southeastern part. These rivers supply sediments to the Gulf of Guinea. The active river system controlled by climate and topographic landscapes accounts for sediment distribution within the continent and offshore areas. Along the stream and river channels there are serious mining of these sediments used for construction purposes. Generally, sites for sand deposition fall into three main categories: 1. the alluvial fan province which is an area proximal to the base of mountains and high-altitude rock outcrops which serve as the major sources of high sediment supply to the rivers. These outcrops include; the weathered Cretaceous rocks of Afikpo Basin and other basement rocks from Obudu Plateau, the Oban Massif and the Cameroun Mountain 2. channelized braided stream sediments and associated overbanks, and, 3. meandering stream province

environmental and mineral exploration significance.

Figure 2. The river configuration within Afikpo town, SE Nigeria.

2. Sedimentation processes

Figure 1. Map of Africa showing the location of Afikpo town and the Cross River flowing south-ward into the Gulf of Guinea.

Sedimentary Processes and Sedimentation in the Shallow Offshore, Eastern Niger Delta, Gulf of Guinea http://dx.doi.org/10.5772/intechopen.74135 59

Figure 2. The river configuration within Afikpo town, SE Nigeria.

of the Benue River, the Afikpo-Cross River, which transport sediments from the hinterland in eastern Nigeria to the eastern offshore area of the Niger Delta. We will discuss the continental, deltaic and shallow marine processes, sediments and their responses from both outcrop and subsurface data. A consideration of the subsurface architecture of shallow marine sediments from the eastern part of the Tertiary Niger Delta sedimentary basin will also be made. The study and understanding of sedimentary processes and their responses have serious economic, environmental and mineral exploration significance.

#### 2. Sedimentation processes

are of significance in the distribution of sediments in the east and western offshore area of the country. The Niger River is active and supplies sediments toward the western part of the Niger Delta, whereas, the Benue River concentrates sedimentation in the eastern offshore (Figure 1) area. There are subsurface evidences of the occurrence of ancient river channels and canyons that served as conduits for transporting sediments from the continent to the Gulf of Guinea [1]. These sedimentation processes are still active today and sediments keep building out along the shores and on the continental shelf of the Niger Delta. We will look at the outcrop evidence of fluvial and marine sandstones at Afikpo Town, and trace the course of the Cross River from Afikpo (Figure 2) to the coastal town of Calabar where presently these sediments are deposited into the estuaries and open marine environments. The subsurface occurrence of shallow marine facies will serve as analogue to the outcrop exposures of marine sandstones in the Afikpo basin. The eastern offshore of the Niger Delta occurs within few kilometers away from the active volcanic line of the Cameroun Mountain. The geomorphic features and surface processes in this region are of interest to most researchers and enables the paleo-reconstruction of subsurface sediments of Tortonian age in the offshore area. The adjacent highland areas consisting of the Precambrian basement of the Oban Massif, Obudu Plateau and the Cameroun Mountain form the sources of weathered sediments that are transported through the Great Kwa and Calabar Rivers to the offshore area south of Calabar Town, South Eastern Nigeria [2]. These rocks are weathered, highly fractured, foliated, and exposed by stream channels cutting through them [2]. They from the major provenance of sediments deposited within the shallow to deep offshore through submarine canyons. In this paper, we will consider a major tributary

Figure 1. Map of Africa showing the location of Afikpo town and the Cross River flowing south-ward into the Gulf of

Guinea.

58 Sedimentation Engineering

Generally, there are two major rivers in Nigeria that run through the country with several tributaries. They are; the Niger and Benue rivers. The Niger river empties into the Atlantic Ocean in the south- western axis of Nigeria, whereas the Benue River in the southeastern part. These rivers supply sediments to the Gulf of Guinea. The active river system controlled by climate and topographic landscapes accounts for sediment distribution within the continent and offshore areas. Along the stream and river channels there are serious mining of these sediments used for construction purposes. Generally, sites for sand deposition fall into three main categories: 1. the alluvial fan province which is an area proximal to the base of mountains and high-altitude rock outcrops which serve as the major sources of high sediment supply to the rivers. These outcrops include; the weathered Cretaceous rocks of Afikpo Basin and other basement rocks from Obudu Plateau, the Oban Massif and the Cameroun Mountain 2. channelized braided stream sediments and associated overbanks, and, 3. meandering stream province that finally discharges into the open sea. The alluvial fan sediments occurred in the hinterland proximal to the Afikpo Basin sedimentary rock outcrops and the basement rocks of the Oban Massif. The Afikpo-Calabar River south-east of Afikpo Town in the South-eastern part of Nigeria possesses high sediment loads that account for the braids deposited within the channel in this area. This area is highly prone to river bank erosion that claims parts of adjacent farmlands (Figure 3). This river maintains a straight course from Afikpo area through Adim town to Etono where the river meanders in the south-west direction as it flows towards Iyakpan. The general trend of the river from Afikpo to Calabar is in the NE-SW direction.

#### 2.1. Braided stream

Braided stream sediments occur within Afikpo Town in both ancient outcrop section and within the recent Afikpo-Calabar River course (Figure 4). The formation of braids usually occurred in areas proximal to sediment provenance with high sediment supply and stream gradient. The channel within this region possesses steep gradient with variations in stream discharge, eroding the river banks at Ndibe Beach (Figure 3) and adjacent lands along the entire river course. The river channel is constantly expanding due to this erosion and has exceeded 100 m in width within Ndibe Beach (Figure 3). The region generally possesses uneven topography due to tectonism and differential weathering of the basement rock along the river channel [2]. The Cretaceous sandstone outcrop in the Afikpo Basin revealed this multi-story braided sediments stacking into about eight braids (Figure 4). These braided stream deposits reflect high sediment supply within the stream channel, great proportions of suspended and bedload load sediments which are the main controlling factors on the development of the ancient river that transported the sediments. Fluvial sediments are widespread in outcrop exposures in Afikpo Town and the various stream sedimentary features at various points along the channel are obvious in the outcrop sections in the area.

approaches Calabar area in the Niger Delta (Figure 5). This river and its tributaries forms the major sediment transporting conduit to the offshore area in the south-eastern Niger Delta and to the Gulf of Guinea. Site for more sediment accumulation within the meandering system is the point bar characterized by poorly sorted, coarse to very coarse-grained sands with gravels deposited in the deeper parts of the meander belt by a slow-moving water along the curve (Figure 6). It grades upward into a very fine grained well-sorted sediment from the deeper part of the channel towards the shallow section with reduced current flow. The amount of suspended sediments guaranteed the deposition of fine grained sands along the meandering curve prompting a swift transition from braided deposition to a meandering configuration. The areas experiencing high degree of meandering along the river course include; south of Afikpo Town, Etono area, Iyakpan, Itu and Ayadeghe with waning energy as it approaches Calabar Town where the river empties into the open sea to deposit its sediments. These sediments are moved oceanward into the Gulf of Guinea through canyon. Some are distributed within the shores by waves, longshore currents and other marine energy fluxes to form beaches as can be seen in Ibeno Beach south of Eket Town in Akwa Ibom State, west of Calabar Town. The ancient river deposits within the shallow offshore in the eastern Niger Delta have

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Figure 4. Stacked multi-story braided channel deposit at MacGregor Hill, Afikpo, SE Nigeria.

The marine portion of the outcrops in Afikpo marks a transition from a more fluvially influenced sedimentation to a deltaic process. This is evident in the isolated lobes of sandstone outcrops that occur within Akpoha area west of Afikpo Town (Figure 7). It may possibly be a

been identified from subsurface data [3].

2.3. Deltaic deposits

#### 2.2. Meandering channels

There are more than seven major meandering loops along this river from Afikpo to Calabar Area (Figure 5). The degree of meandering along this river course increases downstream as it

Figure 3. Ndibe Beach, Afikpo-Cross River area: latitude N05�500 30.400; longitude E-007�560 55.600; elevation is 17 m. The width of the river is more than 100 m. The banks of the river in this area is prone to constant erosion.

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Figure 4. Stacked multi-story braided channel deposit at MacGregor Hill, Afikpo, SE Nigeria.

approaches Calabar area in the Niger Delta (Figure 5). This river and its tributaries forms the major sediment transporting conduit to the offshore area in the south-eastern Niger Delta and to the Gulf of Guinea. Site for more sediment accumulation within the meandering system is the point bar characterized by poorly sorted, coarse to very coarse-grained sands with gravels deposited in the deeper parts of the meander belt by a slow-moving water along the curve (Figure 6). It grades upward into a very fine grained well-sorted sediment from the deeper part of the channel towards the shallow section with reduced current flow. The amount of suspended sediments guaranteed the deposition of fine grained sands along the meandering curve prompting a swift transition from braided deposition to a meandering configuration. The areas experiencing high degree of meandering along the river course include; south of Afikpo Town, Etono area, Iyakpan, Itu and Ayadeghe with waning energy as it approaches Calabar Town where the river empties into the open sea to deposit its sediments. These sediments are moved oceanward into the Gulf of Guinea through canyon. Some are distributed within the shores by waves, longshore currents and other marine energy fluxes to form beaches as can be seen in Ibeno Beach south of Eket Town in Akwa Ibom State, west of Calabar Town. The ancient river deposits within the shallow offshore in the eastern Niger Delta have been identified from subsurface data [3].

#### 2.3. Deltaic deposits

that finally discharges into the open sea. The alluvial fan sediments occurred in the hinterland proximal to the Afikpo Basin sedimentary rock outcrops and the basement rocks of the Oban Massif. The Afikpo-Calabar River south-east of Afikpo Town in the South-eastern part of Nigeria possesses high sediment loads that account for the braids deposited within the channel in this area. This area is highly prone to river bank erosion that claims parts of adjacent farmlands (Figure 3). This river maintains a straight course from Afikpo area through Adim town to Etono where the river meanders in the south-west direction as it flows towards Iyakpan. The general

Braided stream sediments occur within Afikpo Town in both ancient outcrop section and within the recent Afikpo-Calabar River course (Figure 4). The formation of braids usually occurred in areas proximal to sediment provenance with high sediment supply and stream gradient. The channel within this region possesses steep gradient with variations in stream discharge, eroding the river banks at Ndibe Beach (Figure 3) and adjacent lands along the entire river course. The river channel is constantly expanding due to this erosion and has exceeded 100 m in width within Ndibe Beach (Figure 3). The region generally possesses uneven topography due to tectonism and differential weathering of the basement rock along the river channel [2]. The Cretaceous sandstone outcrop in the Afikpo Basin revealed this multi-story braided sediments stacking into about eight braids (Figure 4). These braided stream deposits reflect high sediment supply within the stream channel, great proportions of suspended and bedload load sediments which are the main controlling factors on the development of the ancient river that transported the sediments. Fluvial sediments are widespread in outcrop exposures in Afikpo Town and the various stream sedimentary features at various

There are more than seven major meandering loops along this river from Afikpo to Calabar Area (Figure 5). The degree of meandering along this river course increases downstream as it

30.400; longitude E-007�560

55.600; elevation is 17 m. The

trend of the river from Afikpo to Calabar is in the NE-SW direction.

points along the channel are obvious in the outcrop sections in the area.

Figure 3. Ndibe Beach, Afikpo-Cross River area: latitude N05�500

width of the river is more than 100 m. The banks of the river in this area is prone to constant erosion.

2.1. Braided stream

60 Sedimentation Engineering

2.2. Meandering channels

The marine portion of the outcrops in Afikpo marks a transition from a more fluvially influenced sedimentation to a deltaic process. This is evident in the isolated lobes of sandstone outcrops that occur within Akpoha area west of Afikpo Town (Figure 7). It may possibly be a

Figure 5. Meandering points along the river course from Afikpo town to Calabar. The degree of meandering increases in the south-east direction as the river approaches the sea.

Figure 6. Meandering channel deposit: Fining upward point bar channel deposits showing lag base with very coarse grained, pebbles and gravels (cretaceous sandstone of Afikpo Basin, south-eastern Nigeria).

mouth-bar deposit that occurred towards the end of a distributary channel. It consists of two facies units: a massive planar bed overlying a mega trough cross-beds facies of between 250 and 300 cm thick (Figure 7). The sandstone is underlain by mudstones and shale portraying a coarsening upward sequence in grain size typical of a deltaic environment. A shoreface shallow marine section is observed in the Cretaceous age Amasiri sandstone (Afikpo Basin) showing a large lateral extent of more than 8 km with thickness greater than 100 m (Figure 8a and b).

3. Subsurface sedimentary analogue of eastern offshore Niger Delta

09.900; longitude E-007�520

Stratigraphically, the Niger Delta Basin has three formations. They include; Akata Formation, a prodelta marine shale which is the basal unit; the Agbada Formation, a paralic sequence of

Figure 8. (a) Regressive barrier bars (Amasiri, Afikpo Basin, SE Nigeria). Thickness: over 100 m; width: 3 m; length: (more than 8 km). These regressive bars are underlain by marine shales, (b) shallow marine regressive Amasiri sandstone in Afikpo Basin, SE Nigeria. It is laterally extensive and runs parallel to paleo-coastline. The thickness is above 70 m, more

15.400. Elevation is 67.8 m.

Figure 7. Massive planar beds underlain by cross-bedded sandstone (250–300 cm thick). The sandstone is underlain by

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marine shale—Deltaic environment.

than 3 m in width. N05�530

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Figure 7. Massive planar beds underlain by cross-bedded sandstone (250–300 cm thick). The sandstone is underlain by marine shale—Deltaic environment.

Figure 8. (a) Regressive barrier bars (Amasiri, Afikpo Basin, SE Nigeria). Thickness: over 100 m; width: 3 m; length: (more than 8 km). These regressive bars are underlain by marine shales, (b) shallow marine regressive Amasiri sandstone in Afikpo Basin, SE Nigeria. It is laterally extensive and runs parallel to paleo-coastline. The thickness is above 70 m, more than 3 m in width. N05�530 09.900; longitude E-007�520 15.400. Elevation is 67.8 m.

### 3. Subsurface sedimentary analogue of eastern offshore Niger Delta

mouth-bar deposit that occurred towards the end of a distributary channel. It consists of two facies units: a massive planar bed overlying a mega trough cross-beds facies of between 250 and 300 cm thick (Figure 7). The sandstone is underlain by mudstones and shale portraying a coarsening upward sequence in grain size typical of a deltaic environment. A shoreface shallow marine section is observed in the Cretaceous age Amasiri sandstone (Afikpo Basin) showing a large lateral extent of more than 8 km with thickness greater than 100 m (Figure 8a

Figure 6. Meandering channel deposit: Fining upward point bar channel deposits showing lag base with very coarse

grained, pebbles and gravels (cretaceous sandstone of Afikpo Basin, south-eastern Nigeria).

Figure 5. Meandering points along the river course from Afikpo town to Calabar. The degree of meandering increases in

the south-east direction as the river approaches the sea.

62 Sedimentation Engineering

and b).

Stratigraphically, the Niger Delta Basin has three formations. They include; Akata Formation, a prodelta marine shale which is the basal unit; the Agbada Formation, a paralic sequence of shale and sandstone beds occurring in almost equal proportions, which forms the hydrocarbon habitat in the basin, and finally the youngest continental Benin Formation comprising of loose fluvial sands and gravels [4–10]. There are four unique Members that occur within the Agbada Formation in the eastern offshore Niger Delta. They include; the Qua Iboe Shale, Biafra Member, the Rubble Bed, and the D-1 Sand [3]. The Qua Iboe Shale (QIS) is identified on well log as the first continuous shale interval that occurred towards the base of the continental Benin Formation. The well data used for this study were taken from an oilfield located in the shallow offshore area in the eastern part of the Niger Delta sedimentary basin. The location is about 4 km away from the Calabar Town, just at the mouth of the major estuary where most sediments from the continent are deposited and consequently transported to the deep sea in the Gulf of Guinea.

Studies of modern sedimentary environments revealed that vertical profiles of grain size from a specific environment have certain log characteristics [11–14]. For instance, prograding deltas and barrier bars deposit display an upward-coarsening grain size profiles (Figure 9). Three prominent trends identified on well log that helped to delineate the various depositional settings are: coarsening upward trend representing deltaic facies (Figure 10, number 4).; fining upward trend showing transgressive facies (Figure 10, number 1 and 5), boxcar gamma ray log motif of regressive barrier bar/beach deposits (Figure 10, number 2 and 3).

3.1. Gamma ray log facies description

Figure 10. Specific gamma ray log trends in the study area.

sediments (Figure 11).

delta (Figure 11) [3].

Seven main gamma-ray log characteristics (Figure 11) have been established using gamma-ray log trends; (1) spiky or mixed (2) blocky and coarsening-upward (3) blocky and fining-upward (4) coarsening upward (5) fining upward (6) erratic and (7) blocky [3]. The log facies descriptions below are used to infer genetically related environments. The gamma-ray electrofacies patterns represent environments that range from deltaic front to shallow marine setting.

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Electrofacies 1: This facies is characterized by spiky or mixed gamma ray log signature, which

Electrofacies 2: This facies consists of both a blocky pattern in association with a coarseningupward trend. The repeated blocky pattern may represent amalgamated fluvial (distributary) or estuarine channels, whereas coarsening upward shows seaward progradation of continental

Electrofacies 3: This unit has a sharp lower contact with a weak fining upward trend at the upper boundary displaying a blocky shape typical of distributary channel or tidally influenced

Electrofacies 4: This unit displayed a spiky and coarsening upward gamma ray log motif that may represents a prograding deltaic or a delta front facies (Figure 11) [3]. The environments

may represent middle or lower deltaic plain environment (Figure 11).

Figure 9. Electrofacies patterns showing some distinct depositional environments.

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Figure 10. Specific gamma ray log trends in the study area.

#### 3.1. Gamma ray log facies description

shale and sandstone beds occurring in almost equal proportions, which forms the hydrocarbon habitat in the basin, and finally the youngest continental Benin Formation comprising of loose fluvial sands and gravels [4–10]. There are four unique Members that occur within the Agbada Formation in the eastern offshore Niger Delta. They include; the Qua Iboe Shale, Biafra Member, the Rubble Bed, and the D-1 Sand [3]. The Qua Iboe Shale (QIS) is identified on well log as the first continuous shale interval that occurred towards the base of the continental Benin Formation. The well data used for this study were taken from an oilfield located in the shallow offshore area in the eastern part of the Niger Delta sedimentary basin. The location is about 4 km away from the Calabar Town, just at the mouth of the major estuary where most sediments from the continent are deposited and consequently transported to the deep sea in

Studies of modern sedimentary environments revealed that vertical profiles of grain size from a specific environment have certain log characteristics [11–14]. For instance, prograding deltas and barrier bars deposit display an upward-coarsening grain size profiles (Figure 9). Three prominent trends identified on well log that helped to delineate the various depositional settings are: coarsening upward trend representing deltaic facies (Figure 10, number 4).; fining upward trend showing transgressive facies (Figure 10, number 1 and 5), boxcar gamma ray log

motif of regressive barrier bar/beach deposits (Figure 10, number 2 and 3).

Figure 9. Electrofacies patterns showing some distinct depositional environments.

the Gulf of Guinea.

64 Sedimentation Engineering

Seven main gamma-ray log characteristics (Figure 11) have been established using gamma-ray log trends; (1) spiky or mixed (2) blocky and coarsening-upward (3) blocky and fining-upward (4) coarsening upward (5) fining upward (6) erratic and (7) blocky [3]. The log facies descriptions below are used to infer genetically related environments. The gamma-ray electrofacies patterns represent environments that range from deltaic front to shallow marine setting.

Electrofacies 1: This facies is characterized by spiky or mixed gamma ray log signature, which may represent middle or lower deltaic plain environment (Figure 11).

Electrofacies 2: This facies consists of both a blocky pattern in association with a coarseningupward trend. The repeated blocky pattern may represent amalgamated fluvial (distributary) or estuarine channels, whereas coarsening upward shows seaward progradation of continental sediments (Figure 11).

Electrofacies 3: This unit has a sharp lower contact with a weak fining upward trend at the upper boundary displaying a blocky shape typical of distributary channel or tidally influenced delta (Figure 11) [3].

Electrofacies 4: This unit displayed a spiky and coarsening upward gamma ray log motif that may represents a prograding deltaic or a delta front facies (Figure 11) [3]. The environments

Electrofacies 5: The unit characteristically displayed sharp lower contact with a gradational upper boundary (Figure 11). It is a transgressive unit. The bell-shaped succession usually occurs in three types of environments: tidal channels, turbidite fills and fluvial or deltaic channels. Tidal channels and turbidite fills also commonly include glauconite and shell debris [16]. The only bell-shaped successions with carbonaceous detritus are deposited in environ-

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Electrofacies 6: This is erratic in nature. It may represent a lower deltaic plain to shallow

Electrofacies 7: The electrofacies of this unit shows sharp upper and lower contact (blocky) [3]. The thickness of the boxcar gamma ray log motifs in all the studied intervals is less than 25 m [3]. Mudlog report indicates that the lithologies of these sections are mostly sandstones (off white to creamy white, gray in part, translucent to transparent, very fine to fine, occasionally medium grained, sub-rounded to rounded, sub-spherical, primarily calcareous cement, argillaceous in part poorly to moderately sorted [3], very good porosity and permeability) (Table 1) [3]. In the Yowi field, the boxcar shaped gamma-ray log occurred in all the wells with average thickness of 58 ft. in well A2P2 between the intervals of 3357–3412 ft., 5286–5344 ft., 5750– 5813 ft., 6047–6110 ft. and 6848–6903 ft. Carbonaceous matter, mica and glauconitic materials are also present in the successions (Table 1). The presence of glauconite depicts a marine environment, whereas mica and carbonaceous detritus showed that the sediments were depos-

Sedimentary deposits identified using well log motifs helped in reconstructing sediments that were deposited within the open sea and reworked to confer the various architecture and

> quartz grains, very fine, slightly silty, sub rounded to rounded, well sorted, glauconitic, carbonaceous speckles, micaceous, good porosity and permeability. Oil Shows: Very light brown oil stain, very dull yellow fluorescence, weak diffuse white cut fluorescence, no residue, faint Hydrocarbon odor.

> opaque, quartz grains, very fine, silty in part, with thin Siltstone laminae, sub rounded to rounded, well sorted, micaceous, glauconitic, carbonaceous speckles, traces of pyrite, moderate to good porosity and permeability.

Sandstone: Medium to dark brown oil saturated sandstone, clear, translucent, medium brown, friable to loose quartz grains, very fine to fine, predominantly very fine, sub rounded to rounded, very well sorted, excellent porosity and permeability, micaceous, trace glauconite, trace carbonaceous speckles.  Very strong

A regressive bar

Lower part of a regressive bar

Top of 5.2 sand, a regressive bar

Reservoir interval Core description Remarks

5018–5021 Sandstone: Light to medium brown, friable, clear, translucent, light brown,

5027–5033 Silty Sandstone: Light to medium gray, friable, clear, translucent, Lower part of

ments of fluvial or deltaic channels [11].

ited within the shallow marine/coastal realm.

hydrocarbon odor.

Table 1. Ditch-cutting description of rock samples [3].

3.2. Depositional environments

5042–5045 Well A2P2, N5.2 sand

marine shelf deposits.

Figure 11. Gamma ray log motifs in association.

depicted by this trend could be shoreface, tidal or mouth bar. By the methods reported in [15], the environments of coarsening upward successions can be classified into three general categories: (1) prograding submarine fans (2) regressive barrier bars, and (3) prograding deltas or crevasse splays [3]. Prograding submarine fans and regressive barrier bars are commonly associated with glauconite and shell debris [3, 11, 15, 16]. Glauconite debris occurred in all the samples from about 1800 ft. in all the wells, consequently, there is the possibility of the first two environments (regressive barrier bars or prograding submarine fans) occurring in the field. Deductively, the paleoenvironments of funnel shape facies can be attributed to shallow marine and deltaic front environments. One of the major difference between a prograding delta and a crevasse splay is the scale of deposition; the scope of a prograding delta is comparatively large. The work of [11, 15], shows that environments of funnel-shaped successions with the presence of carbonaceous detritus may be depicted a prograding delta or a crevasse splay [3]. The average thickness of the thin funnel-shaped successions in this work is less than 800 cm, which suggests that the paleoenvironment could be a crevasse splay associated with a deltaic channel. A scale of less than 800 cm is comparatively small to be classified as a prograding delta [3].

Electrofacies 5: The unit characteristically displayed sharp lower contact with a gradational upper boundary (Figure 11). It is a transgressive unit. The bell-shaped succession usually occurs in three types of environments: tidal channels, turbidite fills and fluvial or deltaic channels. Tidal channels and turbidite fills also commonly include glauconite and shell debris [16]. The only bell-shaped successions with carbonaceous detritus are deposited in environments of fluvial or deltaic channels [11].

Electrofacies 6: This is erratic in nature. It may represent a lower deltaic plain to shallow marine shelf deposits.

Electrofacies 7: The electrofacies of this unit shows sharp upper and lower contact (blocky) [3]. The thickness of the boxcar gamma ray log motifs in all the studied intervals is less than 25 m [3]. Mudlog report indicates that the lithologies of these sections are mostly sandstones (off white to creamy white, gray in part, translucent to transparent, very fine to fine, occasionally medium grained, sub-rounded to rounded, sub-spherical, primarily calcareous cement, argillaceous in part poorly to moderately sorted [3], very good porosity and permeability) (Table 1) [3]. In the Yowi field, the boxcar shaped gamma-ray log occurred in all the wells with average thickness of 58 ft. in well A2P2 between the intervals of 3357–3412 ft., 5286–5344 ft., 5750– 5813 ft., 6047–6110 ft. and 6848–6903 ft. Carbonaceous matter, mica and glauconitic materials are also present in the successions (Table 1). The presence of glauconite depicts a marine environment, whereas mica and carbonaceous detritus showed that the sediments were deposited within the shallow marine/coastal realm.

#### 3.2. Depositional environments

depicted by this trend could be shoreface, tidal or mouth bar. By the methods reported in [15], the environments of coarsening upward successions can be classified into three general categories: (1) prograding submarine fans (2) regressive barrier bars, and (3) prograding deltas or crevasse splays [3]. Prograding submarine fans and regressive barrier bars are commonly associated with glauconite and shell debris [3, 11, 15, 16]. Glauconite debris occurred in all the samples from about 1800 ft. in all the wells, consequently, there is the possibility of the first two environments (regressive barrier bars or prograding submarine fans) occurring in the field. Deductively, the paleoenvironments of funnel shape facies can be attributed to shallow marine and deltaic front environments. One of the major difference between a prograding delta and a crevasse splay is the scale of deposition; the scope of a prograding delta is comparatively large. The work of [11, 15], shows that environments of funnel-shaped successions with the presence of carbonaceous detritus may be depicted a prograding delta or a crevasse splay [3]. The average thickness of the thin funnel-shaped successions in this work is less than 800 cm, which suggests that the paleoenvironment could be a crevasse splay associated with a deltaic channel. A scale of less than 800 cm is comparatively small to be classified

as a prograding delta [3].

Figure 11. Gamma ray log motifs in association.

66 Sedimentation Engineering

Sedimentary deposits identified using well log motifs helped in reconstructing sediments that were deposited within the open sea and reworked to confer the various architecture and

Table 1. Ditch-cutting description of rock samples [3].

configurations of the deposits [3, 17]. Well log correlation revealed sand bodies displaying lateral continuity across the field (Figures 12 and 13). The Qua Iboe Shale (QIS) forms a key stratigraphic marker across the field that delimits the marine sediments from the continental deposits. The top and base of key sand units are used for correlation base on gamma ray trends (Figure 12). Each depositional stack (parasequence) is unique to guide sand body correlation thereby complementing the traditional lithostratigraphic correlation. High gamma ray (with a cut-off of 75 0 API value and above) corresponding to the shale base line indicates shale lithology. In the sequence of the various major environments, there is swift transition from fluvial to marine. The fluvial section occurred at the top of the Qua Iboe Shale which demarcated the continental sediments from the marine section (Figure 13). The marginal marine segment comprises of the coastal plain sands, whereas delta front sandstones occurred within the shallow marine realm (Figure 13). The delta front sandstone is characterized by thicker, cleaner and more shale-free sandstones than the coastal plain sands (Figure 13).

From the perspective of facies models, layer-caked shore-parallel facies have been assumed to form homogenous, uniform reservoirs with high production capacities. Wave-influenced coastline

deposits possess distinct facies with homogenous beach and shoreface sands accumulating on the updrift side of the river mouth with significantly more heterogeneous facies on the downdrift side. The heterogeneous unit is noticed towards the lower parts of the reservoirs (N4, N5, and N5.2) in wells A2P2 and A9P2 (Figure 9). The thick shale segments within each sequence are interpreted to

Figure 13. E-W correlation showing increasing shale thickness towards the west (A9P2) and increasing thickness of

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The well log signature of the continental fluvial environment of the Benin sand shows a jagged log motif, a typical characteristic of siliciclastic fluvial environment [3]. It occurred above the top of Qua Iboe Shale Member (QISM) at 1850 ft. (Figure 13) [3]. Different subenvironments that occurred within the Benin Formation include; braided stream, channel fills, flood plain, meandering channels, point-bar, etc. [3]. For example, sand beds that indicate meandering channel system consist of an alternation of fining-upward (Figure 11), channel fills and mud dominated floodplain deposits [3]. Braided fluvial systems are often composed of amalgamated channel fills, which confer a blocky pattern to the well logs [3]. In contrast, other types of rivers, including fine grained meandering or flashy ephemeral, produce a more irregular, jagged type of motif on well logs (Figure 11, number 1) [3]. Relatively thin-bedded (m scale) coarsening-upward sand units may also occur in fluvial successions relative to crevasse splays in a low-energy and confined meandering system [3, 18]. The ditch cutting description for the

sandy section shows sand dominated by Quartz grains (Table 1) after [3].

be shelf or deep marine deposits.

coastal plain/deltaic front sandstones towards the east.

3.2.1. Fluvial sediments

Figure 12. E-W Litho-correlation of key sand bodies across the field.

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Figure 13. E-W correlation showing increasing shale thickness towards the west (A9P2) and increasing thickness of coastal plain/deltaic front sandstones towards the east.

deposits possess distinct facies with homogenous beach and shoreface sands accumulating on the updrift side of the river mouth with significantly more heterogeneous facies on the downdrift side. The heterogeneous unit is noticed towards the lower parts of the reservoirs (N4, N5, and N5.2) in wells A2P2 and A9P2 (Figure 9). The thick shale segments within each sequence are interpreted to be shelf or deep marine deposits.

#### 3.2.1. Fluvial sediments

configurations of the deposits [3, 17]. Well log correlation revealed sand bodies displaying lateral continuity across the field (Figures 12 and 13). The Qua Iboe Shale (QIS) forms a key stratigraphic marker across the field that delimits the marine sediments from the continental deposits. The top and base of key sand units are used for correlation base on gamma ray trends (Figure 12). Each depositional stack (parasequence) is unique to guide sand body correlation thereby complementing the traditional lithostratigraphic correlation. High gamma ray (with a

lithology. In the sequence of the various major environments, there is swift transition from fluvial to marine. The fluvial section occurred at the top of the Qua Iboe Shale which demarcated the continental sediments from the marine section (Figure 13). The marginal marine segment comprises of the coastal plain sands, whereas delta front sandstones occurred within the shallow marine realm (Figure 13). The delta front sandstone is characterized by thicker,

From the perspective of facies models, layer-caked shore-parallel facies have been assumed to form homogenous, uniform reservoirs with high production capacities. Wave-influenced coastline

cleaner and more shale-free sandstones than the coastal plain sands (Figure 13).

Figure 12. E-W Litho-correlation of key sand bodies across the field.

API value and above) corresponding to the shale base line indicates shale

cut-off of 75 0

68 Sedimentation Engineering

The well log signature of the continental fluvial environment of the Benin sand shows a jagged log motif, a typical characteristic of siliciclastic fluvial environment [3]. It occurred above the top of Qua Iboe Shale Member (QISM) at 1850 ft. (Figure 13) [3]. Different subenvironments that occurred within the Benin Formation include; braided stream, channel fills, flood plain, meandering channels, point-bar, etc. [3]. For example, sand beds that indicate meandering channel system consist of an alternation of fining-upward (Figure 11), channel fills and mud dominated floodplain deposits [3]. Braided fluvial systems are often composed of amalgamated channel fills, which confer a blocky pattern to the well logs [3]. In contrast, other types of rivers, including fine grained meandering or flashy ephemeral, produce a more irregular, jagged type of motif on well logs (Figure 11, number 1) [3]. Relatively thin-bedded (m scale) coarsening-upward sand units may also occur in fluvial successions relative to crevasse splays in a low-energy and confined meandering system [3, 18]. The ditch cutting description for the sandy section shows sand dominated by Quartz grains (Table 1) after [3].

#### 3.2.2. Deltaic and shallow marine sediments

The deltaic front environment is highly unstable due to the variety of processes operating within this realm. A combination of marine and fluvial influences account for the depositional styles within the marginal marine. Studies on modern sedimentary environments revealed that vertical profiles of grain size from a specific environment have certain log characteristics [3, 11]. Hence, prograding deltas and barrier bar deposits have coarsening upward grain size trends (Figure 12, number 4) [3, 19]. Gamma ray motifs with a bell-shape reflects a gradual vertical transition from shale to sandstone, whereas an upward increase in sand-size is indicative of a gradual change in the energy level of the depositional milieu, and no unique SP-curve pattern is representative of any specific depositional environment [12]. However, when these patterns are integrated with the presence or absence of glauconite and/or carbonaceous detritus from cuttings, a more meaningful and reliable interpretation emerges [20]. The presence of glauconite is observed in ditchcutting samples from studied wells in the field at about 1800 ft., which is the base of Benin Formation and the beginning of the marine sequence. The highest occurrence of glauconite is reported at 2005 ft. It has been consistently recorded from the uppermost part of the Agbada sand sequence down hole, signifying a more marine influence than fluvial or deltaic. The associated environments based on log shapes and the presence of glauconite within this interval in the study area include [3]; beach, barrier foot, offshore/regressive bars, and shoreface deposits. bars. Most of the log facies units displaying erratic/fining upward motifs are representatives of tidal events. The ancient and recent sediments identified in the area form the major sources of sand used for construction purposes. Some essential minerals are also concentrated in these sedimentary units. In the subsurface, the sediments form reservoirs for

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The author acknowledges the O.B Lulu Briggs Chair in Petroleum Geoscience at the Institute of Petroleum Studies, University of Port Harcourt, Nigeria, for providing the platform for carrying out the subsurface studies. The occupant of the O.B Lulu Briggs Chair, Prof. Minapuye I. Odigi, is also acknowledged for supervising the project. The following persons are recognized for their encouragement and comfort throughout the period of this research: Mrs. Perfect Suka, Ms. Victory Suka and Ms. Virtue Suka. This project was supported finan-

cially by Engr. LeBari Nania of the Nigerian Agip Oil Company.

The author declares that no conflict of interest exists.

Address all correspondence to<EMAIL_ADDRESS>
Geoscience. 2015, Science Publication (under review)

Exploration Department, Belemaoil Producing Limited, Port Harcourt, Nigeria

[1] Petters SW. An ancient submarine canyon in the Oligocene-Miocene of the western Niger Delta. Sedimentology. 1984;31:805-810. DOI: 10.1111/j.1365-3091. 1984.tb00887

[2] Momta PS, Essien NU. The geology and structural evolution of the Aningeje Metasediment in the lower part of the Oban massif, SE Nigeria. Journal of Geography, Environment and Earth Science International. 2015, 2016;4(1):1-16. DOI: 10.9734/JGEESI/2016/19888 ISSN:

[3] Momta PS, Odigi MI. Reconstruction of the depositional setting of Tortonian sediments in the Yowi field, shallow offshore Niger Delta, using Wireline logs. American Journal of

hydrocarbon accumulation.

Acknowledgements

Conflict of interest

Author details

Prince Suka Momta

References

2454-7352

#### 4. Conclusions

The Cretaecous exposure in Afikpo Basin South Eastern Nigeria comprises of sediments of fluvial, deltaic and marine origin. Ancient fluvial deposits in the area contains both braided stream and point bar channel sedimentary units. These deposits are also observed in the recent fluvial process that is continuously transporting sediments from the highland into the open sea in the offshore of the eastern Niger Delta through the Afikpo-Cross River. This has significant implications for paleo-environmental reconstruction of the subsurface formations of the Niger Delta. Subsurface data from an offshore field south of Calabar Town revealed the architecture of sediments probably of fluvial, deltaic and marine origin.