Lake delta biomorphodynamics under changing inflow scenarios: the case of Lake Turkana, Kenya

Abstract:

Lake Turkana is located in Northern-Western Kenya and is the world’s fourth largest lake (closed basin) measuring 200 km by 40 km. The lake is fed predominantly by the Omo River, which flows in Ethiopia. The use of its waters for energy production and irrigation has created potential transnational and interregional political and economic tensions, exacerbated from December 17^th, 2016 by the start of operations of the third dam built on the Omo River. Previous research has shown that the dam and irrigation efficiency could have significant impacts on Lake Turkana’s water level causing significant shoreline recession and morphological changes in the delta of the Omo River.

In this work we use multispectral satellite data to investigate how vegetation dynamics, river hydrology and sediment load interact, to determine the morphological evolution of the Northern section of Lake Turkana, Kenya. The aim of the work is to use such information to explore the effect of Omo River headwaters impoundment on the downstream water, sediment and vegetation dynamics controlling the delta evolution. This is also crucial to understand how changes in lake morphodynamics and vegetation patterns will affect groundwater recharge and thus the underground springs that are an important irrigational source for the communities populating the lake shores.

The analysis of multiband satellite imagery has allowed us to extract information on land coverage, namely vegetation, water and bare ground for the study area over the period of analysis. Temporal changes in vegetation spatial patterns and lake morphology associated with the historical hydrological signal have revealed the existence of four evolutionary phases for the delta of Turkana Lake. In particular, during the last phase, the reduced water flow and sediment supply due to the construction and the filling of the dams have progressively lowered the lake water depth and reduced the morphodynamic activity of the delta.

Our analysis shows that in order to have complex morphological structures and land and lake equilibrium, the lake should not become too shallow, and periodical overflows either from the river or the lake should be maintained. This will sustain shallow groundwater table levels and provide fine sediment during floods thus also benefiting agriculture activities along the shore.