Enhancing Groundwater Recharge Estimation in Otukpo Basin through a Modified Soil Moisture Balance Approach.
Abstract:
This study focuses on estimating groundwater recharge in the Otukpo basin, located in the Middle Belt region of Nigeria, which experiences a tropical climate characterized by distinct dry and wet seasons. A modified daily soil moisture balance model, relying on a single soil water store, was developed using Python programming language and employed to estimate various soil properties such as field capacity, permanent wilting point, readily available water, actual and potential evapotranspiration, and soil moisture deficit. The model also incorporated a new element called “near surface storage,” which accounts for continuing evapotranspiration on days following heavy rainfall, even when the soil moisture deficit remains high.
To estimate runoff, the model utilized runoff matrix and runoff coefficients, which were dependent on rainfall intensity and soil moisture deficits. The groundwater recharge estimation was carried out specifically for cassava and yam, two commonly cultivated vegetable crops in the study area. The analysis was based on meteorological data collected from 2008 to 2018.
The results of the model indicated variations in annual groundwater recharge over the years. For instance, in the water year 2009, the annual groundwater recharge was approximately 333.35 mm, accounting for just 20.01% of the annual rainfall. On the other hand, the water year 2017 recorded the lowest annual groundwater recharge of about 38.119 mm, equivalent to 3.6% of the annual rainfall. Similarly, the highest annual rainfall depth was observed in 2009 at 1665.4 mm, while the lowest occurred in 2017 at 1062.4 mm.
Furthermore, the study found that the annual runoff ranged from 322.04 mm in 2015, comprising 32.16% of the annual rainfall for that year, to 935.56 mm in 2008, which accounted for 58.17% of the annual rainfall. The actual evapotranspiration (AE) also exhibited variations, with the lowest AE observed in 2017 and the highest in 2012. The AE ranged from 583.84 mm in 2017 to 721.39 mm in 2012.
In conclusion, the developed model provided a simplified approach for estimating groundwater recharge and runoff depth, while also establishing the relationship between rainfall and runoff. The findings contribute to a better understanding of the hydrological dynamics in the Otukpo basin and can be valuable for water resource management in the region.
Enhancing Groundwater Recharge Estimation in Otukpo Basin through a Modified Soil Moisture Balance Approach.