Impact of Water Abstraction on the Water Level of Lake Ziway, Ethiopia

Abstract

Significant change has been observed in the water level of Lake Ziway in Ethiopia which hinders its services for a wide variety of ecosystems. However, the contribution of water withdrawal and its impact on the lake water level variation has not been quantified yet. In this study, we conducted a water abstraction survey (WAS) to estimate actual water withdrawal from the lake. Then, we applied a water balance model coupling with simulated river inflow from rainfall-runoff model output data to evaluate the isolated impact of water withdrawal on the lake water level from 1986-2000 at monthly time steps. The amount of water withdrawal from the lake for irrigation water use is 37 10 6 m 3 per year. This led to 0.36 m drop in the lake level which corresponded to 18 km 2 reductions in the lake surface area. This consequently resulted in a reduction of mean annual lake volume by 162 10 6 m 3 from 1986-2000, which accounts for 23% of the total lake inflow from rivers.The results indicate that abstraction from the lake is a significant contributor to the drop in water level of Lake Ziway. This calls for serious action on the management of water abstraction from the lake.

Gap and opportunity analysis of hydrological monitoring in the Ziway-Shala Sub-basin, Ethiopia

“…It is mainly fed by the Katar and Meki rivers, which drain the highlands on the East and West of the Central Rift Valley, respectively (Hengsdijk and Jansen 2006). Based on simulated time series (1986-2014), the average annual inflow from gauged and ungauged catchments is approximately 269 Mm 3 for Meki and 438 Mm 3 for Katar (Goshime et al 2020b).…”

“…• Abstraction: Water abstraction surveys (Goshime et al 2020b). Notes: For an equilibrium system, changes in lake storage are expected to be zero.…”

“…According to the Rift Valley Lake Development Master Plan, issued by MoWR, population is expected to increase at a rate between 2.8% and 3.4% by 2020 (Halcrow 2009). As a result, more and more people are claiming agricultural land for food production (Goshime et al 2020b). In the uplands of the sub-basin, rain-fed agriculture is dominant and typical crops cultivated include maize, wheat and teff (Meijeren and Van Der Poel 2019).…”

“…From remote sensing images, it was identified that this area has increased now to approximately 75 km 2 . However, based on a water abstraction survey conducted by Goshime et al (2020b), Lake Ziway is supplying water to 20 km 2 of irrigated land excluding the irrigated area around Bulbula River at the outflow of the lake. This large deviation between irrigated areas reported by different analyses indicates the need for further validation of the methods used for monitoring.…”

“…more than 50% of irrigation water use around Lake Ziway, according to water abstraction surveys conducted by Goshime et al (2020b). Moreover, several commercial farms use surface water for large-scale horticultural and floricultural production (Seyoum et al 2015).…”