Hydrological System and Water Balance of Ungauged Crater Lakes of the Northern Crater Highlands

Abstract

The study aimed to unveil the hydrological system and water balance of the ungauged crater lakes with major focus on the Emakati Lake which occupy 46% of the Empakaai Crater associated to the East African Rift Valley and form part of the Northern Crater Highlands. Water samples for analysis of NO3- , Cl- and stable isotopes (2H and 18O) were collected from the Emakat lake, springs of the inner, outer and the foot of the Empakaai Crater rims. A combination of satellite data such as digital elevation model (DEM), Climate Hazards Group Infrared Precipitation with Station data (CHIRPS), net shortwave solar radiation, surface temperature, and the computation methods such as Curve Number (CN) Model, DeBruin–Keijman (D-K) Model enabled the computation of water balance components such as Lake level changes, precipitation, runoff and evaporation. Results show that, evaporation (1694.57 mm) surpasses rainfall (878.68 mm) of the Empakaai Crater results of higher enrichments of δ18O and δ2H in the lake ranging between 3.28⁰/₀₀ to 3.96⁰/₀₀ and 31.99 to 33.93⁰/₀₀ compared to springs which range between -5.18 to -4.05⁰/₀₀ and -26.62 to -19.48⁰/₀₀ respectively. Springs plots to the left and above of both the GMWL and TMWL, implying that they receive direct recharge from rainfall. The water balance in the area shows that, groundwater flow plays a major role on the lakes hydrological system as it contributes about 22,004,361.12 m3/year as the groundwater inflow to Emakat Lake which is about 56% of the lake’s total inflow and about 22,734,274.00 m3/year as groundwater outflow which is about 63% of total lake outflow. This imply that, the lake depends less on the weather condition and hence ensuring the sustainability of the ecosystem of the Empakaai crater and the downstream.