An Assessment of the Role of Water Hyacinth in the Water Level Changes of Lake Naivasha Using GIS and Remote Sensing

Abstract

Lake Naivasha is an important water resource for Kenya being a fresh-water lake in a region dominated by saltywater lakes. The lake supports several human activities around it. Its water level, though fluctuates, was gradually declining before 2010. The water level rose from March 2010 and has since remained relatively high. As a result, areas around the lake that were previously land surface are currently submerged in water. This is threatening the survival of human activities around the lake. Consequently, the study sought to establish the causes of the lake’s water level fluctuations in the period 2000-2016, focusing on the role of rainfall, temperature, human activities around the lake, and water hyacinth. Surface area of the lake covered by water and surface area of the lake covered by water hyacinth were extracted from Landsat images. The SEBAL model was used to estimate evaporation potential over the lake and differences in evaporation over areas covered by water hyacinth and open water surfaces were analysed. Water hyacinth cover was found to have significant, positive correlation with monthly average water levels (p < .05). Open water surfaces lost significantly higher water volume through evaporation than areas covered by water hyacinth (p < .05). This suggests that water hyacinth contributes to the high water levels. Rainfall received over Nyandarua slopes, which is the catchment region for in-flow rivers was also an almost statistically significant contributor to lake’s water level changes, while temperature was not. On the other hand, growing human activities around the lake seemed to contribute to water level decline through increasing abstraction from the lake. The study recommends more research on, and implementation of better and more ecologically efficient measures for controlling water hyacinth growth in Lake Naivasha.