Patterns of infiltration on a bench terraced hillslope of Kigezi highlands

Abstract

The patterns of infiltration process on bench terraced hillslopes in the Kigezi highlands are not fully understood. Yet, steady state infiltration is among the major hillslope processes which affect hillslope hydrology, terrestrial ecosystem, slope stability. This study was designed to determine the spatial patterns of steady state infiltration rates on a hillslope; assess the effect of soil properties on steady state infiltration, and evaluate the performance of selected infiltration models. The bench terraced hillslope was stratified into three positional segments, Upslope, Middle slope and Downslope. In each hillslope position, a bench terrace was selected which was also stratified into three segments namely the Upper, the Middle, and the Bottom. Three infiltration experiments were replicated to each of these bench terrace segments of (upper, middle and bottom) to ascertain the intra-bench and inter-bench steady state infiltration rates. The field experimental design for determining steady state infiltration entailed three slope segments, three bench terraces and three replications culminating into a total of 27 measurements. The infiltration measurements were conducted using a double ring infiltrometer. A total of 54 samples each infiltration experiment, two soil samples were picked at two soil depths (0-15cm, and 15-30cm) to establish the influence of soil properties on infiltration. There was a significant (P<0.018) variation in the spatial patterns of steady state infiltration rates from 5cm hr-1 to 40cm hr-1 between the bench terrace positions on the hillslope, with a mean rate of 21cm hr-1. However, Intra-bench steady state infiltration rates varied higher in the bottom segments compared to upper and middle segments especially in the upslope where rates varied from 6cm hr-1 to 20cm hr-1 with (CV=45%). The clay content in the soil had a significant influence (P<0.003) on infiltration in the study sites of the hillslope with a correlation coefficient (R, r2=-0.5). The precision of the three selected infiltration models was good with mean R2 values ranging from 0.93 to 0.99 and RMSE (cm min -1) ranging from 0.015 to 1.4. Although the overall performance of Phillip and Green and Ampt were also satisfactory, Kostiakov had the best precision, model fit and least bias.