River delta slope offshore, waves will make river deltas smoother. Waves can also be responsible for carrying sediments away from the river delta, causing the delta to retreat. For deltas that form further upriver in an estuary, there are complex yet quantifiable linkages between winds, tides, river discharge, and delta water levels. Erosion is also an important control in tide-dominated deltas, such as the Ganges Delta, which may be mainly submarine, with prominent sandbars and ridges. This tends to produce a "dendritic" structure. Tidal deltas behave differently from a river- and wave-dominated deltas, which tend to have a few main distributaries. Once
Saskatchewan River Delta such that normally high spring and summer flows are significantly diminished. Removal of sediment outflow by impoundment has caused enlargement of channels downstream of the dam and reduction of sediment-borne nutrients to the delta ecosystem. In addition, suppression of annual discharge peaks has reduced the frequency of overbank flooding and, consequently, the frequency at which water and nutrients are replenished in the delta wetlands. Reduction of peak flows to the delta is exacerbated by the Gardiner dam on the South Saskatchewan River whose impoundment, Lake Diefenbaker, is nearly five times larger than the Tobin Lake reservoir, with a commensurately larger