GROUNDWATER RECHARGE ESTIMATION AND TREND ANALYSIS USING HYDROLOGICAL AND SOIL MOISTURE BALANCE MODELS IN SEMI ARID REGION

Abstract

Groundwater recharge estimation becomes very important, particularly in a cultivated land mass owing to the roles played by groundwater in the area of agricultural productivity. This paper presents the estimation and trend analysis of groundwater recharge in Kwadna basin using modified soil moisture balance model between the years 1996 and 2016. A single layer soil water balance model coupled with hydrological models was used in the recharge estimation while statistical techniques were used in groundwater recharge trend analysis. The meteorological data used in the models were obtained from Nigeria Meteorological Agency, Minna for the entire study period. Potential evapotranspiration (ETp) on daily basis was also estimated using Hargreaves evapotranspiration equation. Soil properties like moisture content at both field capacity and wilting point, near surface storage, soil moisture deficit, and crop properties like crop rooting depth and crop growth stages were obtained from the past studies and information gathered from the farmers in the study area. The results showed that annual groundwater recharge varied from 156 mm in 2004 to 731 mm in 2012 which correlated positively with rainfall. The soil moisture balance model

results indicated the period of June to September each year when SMD<TAW. The groundwater recharge trend analysis recorded an increasing trend with statistical significance in the two statistical tests used. Thus, the higher groundwater recharge and its increase in trend observed was attributed to higher rainfall depth recorded within the study period in the study area.