Water Budget Analysis of Agulu Lake in Anambra State, Nigeria

The elements of water budget equation were analyzed for the Agulu lake area and underlying aquifers. The water budget implications for soil and gully erosion were evaluated in relation to the geological formations and hydrogeotechnics. Results show that rainfall constitutes the main source of precipitation. It ranges from 1714.04mm to 1995.53mm annually. The potential groundwater aquifer volume is 1.5 X 10⁷m³. Discharge from aquifers contributes 7.4 X 10⁷m³ water annually. The amount of 1.72 X 10⁵m³ that is 60% of precipitation is lost to evaporation; 17 to 21% to infiltration. The quasi steady state of the lake water level and volume shows surface and groundwater continuity as explained by the small difference between total input and output values of the computed water budget of the lake and the aquifer. Flood studies indicate that 19.5% of the annual precipitation constitutes runoff, the main agent of gully and soil erosion, flooding and landslides. The other factors that control the distribution and location of gullies are lithologic and stratigraphical, while topography/geomorphology controls gully distribution within various geologic units. A typical gully is about 500m X 50m X 30m long, wide and deep respectively. The destruction to life and property by runoffs/floods demands joint and sustained efforts by the community dwellers, NGOs, Local Government Areas, State governments, Federal Government and the International Communities.