VARIATIONS OF WAVE-ENERGY LEVELS AND COASTAL SEDIMENTATION, EASTERN NICARAGUA

Abstract

High rates of weathering, abundant rainfall, and high discharge rates combine to supply large volumes of sediment to the coastal zone of eastern Nicaragua. This terrigenous sediment is confined to a narrow section of the inner shelf (<30 km wide) due to the circulation pattern within a coastal boundary layer. Sediment transport within the inner shelf and shore zone is to the south. This simple transport pattern is considerably modified by variations in wave-energy levels that are a function of shelf width, bottom friction, and wave sheltering. In northern sections, the shelf is up to 200 km wide but narrows to less than 20 km in the south. A direct result is that wave-energy levels at the shoreline are of the order of three times greater in the south. In the north the Rio Coco delta is propagating seaward in a fluvially dominated environment, whereas the Rio San Juan delta in the south has a wave-dominated morphology characterized by deflected distributaries. Other major accumulation features have developed where wave-shadowing is produced by offshore reefs and cays. Alongshore a spatial variation was recorded, with straight beaches and simple linear bars in the north that change to rhythmic beach topography and crescentic nearshore bars as wave-energy levels increase toward the south.