Simulated interflow measurements on selected landuse types in the Kuils-Eerste River Catchment, Western Cape, South Africa

Abstract

Hillslope hydrology over the last few decades has attracted much attention which is not surprising considering that they dominate the hydrological processes of catchments all over the world. The complexity of the hillslope with its various processes influences the water movement when it enters and migrates through this fundamental landscape unit. The subsurface flow of this water movement is considered a vital process in runoff generation on hill slopes. Determining the hydraulic behaviour of soils on hillslopes in situ has increased tremendously over the years. This type of flow is generated by various mechanisms due to the antecedent conditions present on the surface and subsurface. The main objective of the study is to understand and characterise the in situ hydraulic behaviour of soils along hillslopes with various conditions present respectively. Secondly, to assess whether the hillslope infiltrometer is a viable instrumentation to be used for these in situ estimation. The studied system is situated on the Zevenwacht Wine Estate Farm located in the KuilsEerste River catchment in the Western Cape. These hillslopes were selected with various land cover/land use present which include natural vegetated areas and cultivated areas subjected to agricultural practices. Three different plots were selected along these hillslopes. By investigating the different factors of water movement through the hillslope system, the hydrologic response and the impact of the various land cover/land use practices on these hillslope systems were determined. The hillslope infiltrometer were used to determine in situ hydraulic behaviour of these hillslopes with soil physical data collected. The results showed that intertlow will not occur as a shallow subsurface flow in the soil matrix for all hillslope sites, respectively. This is due to the soil physical properties which indicated that the sites are characterised by deep highly permeable and porous soils (sandy loam and loamy sand) with low clay contents. The absence of a less permeable soil horizon was also observed which further reduced the possibility of interflow being produced. Therefore, the vertical flow direction was considered to be dominant. Even though interflow could not be estimated, the hillslope infiltrometer still proved to be useful in estimating the in situ hydraulic behaviour of these hillslope soils.