River delta eco-morphodynamics under changing scenarios. The case of
Lake Turkana, Kenya
Abstract
In this work we explore the impact that changes in local climate and
river hydrology have on the morphodynamics of a river delta,
particularly focusing on the evolution of the delta generating at the
lake inlet. We investigated the case of the delta in the lower reach of
the Omo River in Ethiopia, which flows into Lake Turkana, Kenya. The
lake is the fourth largest lake and the largest desert lake in the
world. This case study is of particular interest because within the last
decades three dams have been built within the Omo basin. To quantify
changes in land use and river morphology and relate these to river
hydrology we collect a historical dataset by combining information from
different satellite sources. We observed that the amount of bare
sediments progressively diminished and the biomass became more dense
compared to the existence of sparse biomass in the past. We argue that
this is due to the new river hydrology and sediment load imposed by the
dam, which increased sediment erosion by deepening the channel. The dam
also increased the low flow and reduced peak during flood season
reducing the natural oscillations of the water table and the possibility
to plant was removed during floods. We also indicate that the new
hydrology and reduced sediments have changed, respectively, the
downstream (e.g. lake level), and upstream (e.g. mouth bar deposition)
boundary conditions controlling the evolution of the delta structure. As
a result, the delta morphology became less dynamic and less complex.