UPFLOW model prediction of capillary rise into root zone soil moisture for shallow water table soils of Obio Akpa river floodplain in the Niger-Delta environment, Nigeria.

Abstract

UPFLOW model was used to provide assessments of capillary rise into root zone soil moisture in shallow water table soils of Obio Akpa river floodplain using drum-culture lysimeters. Soil moisture depletion experiment was undertaken through the use of drums with bases intact and drums with bases removed and sunk in the field at different depths during the dry period with no rainfall and no irrigation. UPFLOW model was validated by comparing simulated capillary soil moisture values from a falling water table with gravimetrically observed data from 0 – 500, 500-1000 and, 1000-1500 mm water table  depth in sandy loam and sandy clay soils. Simulated runs mimic the observed fluctuations and trend of capillary rise to the root zone. The statistical pointers of simulation performance showed that good inter-relation exists between observed and simulated vales for both sandy loam and sandy clay soils respectively. The index of agreement, d (0.9989 and 0.9948) shows a good performance of the model for both sandy loam and sandy clay soils respectively. Model efficiency value of about 99.75 and 99.48 % for both the sandy loam and sandy clay soils respectively indicate that the performance of UPFLOW model in simulating capillary rise is satisfactory. Hence, UPFLOW can be used with confidence in simulating capillary rise to the root zone in Obio Akpa, Nigeria.