The Eco-hydrology of Lake Naivasha: A focus on sediment deposition and aggregation to investigate changes in water volume and methods of continual long term monitoring.

Abstract

Lake Naivasha is an important economic asset for Kenya; it currently supports a growing population, a thriving tourism industry, geothermal energy production and over 60 flower farms which predominantly export to Europe. Recent declines in lake level and water quality have led to a marked increase in scientific studies with a common goal to improve management and conservation. The lake is vulnerable to long, hot periods with low rainfall, which increases evaporation rates resulting in concentrations of pollutants in the water rising. The effect of variations in water quality and availability are both felt locally and internationally. While the flower farms and other abstractive industries are easy to blame for the lakes decline in water level, sediment deposition is, and has been, occurring since the formation of Lake Naivasha. Changes in sediment load and streamflow are indicative of the health of the upper catchment. Upstream land usage has changed from natural forests and open land to farming and anthropogenic uses and due to erosion, riverine loads have increased in recent decades. By using remote sensing and coring, this study sought to identify areas of sediment deposition and quantify recent changes in deposition rates due to upstream erosion events or changes in land-management practices. A novel low-cost and easily replicable remote sensing technique was developed successfully to quantify deposition rates. Sedimentation was found to be most prominent in the northern area of Lake Naivasha at an average of 23 mm yr-1, displacing 308139 m³ of water each year. Current management plans set abstraction quotas using lake level measured in metres above sea level. While long-term fluctuations of lake-levels are consistent or perhaps even increasing, lake volume may in fact be slowly declining. This paper recommends that regular satellite and sonar remote sensing could be key to monitoring the health of the basin as well as effectively improving the management of Lake Naivasha which will ensure the long-term existence of the resource and the population and industry it supports.