Interpreting soil and topographic properties to conceptualise hillslope hydrology

Abstract

The sustainability of agricultural practices is enhanced when vegetation makes optimal use of natural hydrological processes. For example, planting tree belts where slope gradient sharply decreases can enable harvesting of run-on water. This can be beneficial for example in reducing water logging and enhancing tree production. There is a need for rapid and low cost identification of water flow paths and conceptualisation of hillslope hydrology so that local landuse planning can reflect such opportunities. The collection of detailed hillslope hydrological data is prohibitively expensive for such applications and so the use of soil morphology and visual observation of topography and surface condition is evaluated as an alternative.At a study site in south eastern Australia the soil physical profile was described down a hillslope with additional measurements of the hydraulic conductivity, bulk density, cation exchange capacity, electrical conductivity, and particle size distribution of the key horizons. This data was used to identify the perceived significant hydrological flow paths down the hillslope. Measurement of the surface runoff, subsurface lateral flow, and the distribution of saturation measured in piezometers were subsequently used to test the conceptual hydrological model. Soil morphology, particularly the soil colour and presence of redox concretions were useful in identifying the locations and depths where saturation and lateral flow occur. The morphology provides an integrated reflection of the dominant hydrological conditions, but care must be taken to ensure that the observations reflect the current hydrological environment and not relic conditions. Other collaborating information such as the history of geomorphological events at the site, a validation of plausible water sources for the potentially transmitting layers, surface soil condition and landholder observations give improved confidence. Combining soil morphological understanding with visual observations of other site characteristics enabled rapid conceptualisation of hillslope hydrological behaviour as needed for local landuse planning.

Spatial soil information in South Africa: Situational analysis, limitations and challenges

“…34 Water is a primary agent in soil genesis, resulting in the development of soil properties containing unique signatures of the way they were formed. Interpretation of soil properties can therefore serve as an indicator of the dominant hydrological processes 35,36 and assist in the structuring and configuration of hydrological models. 37 Hydrologists agree that soil properties and their spatial variation should be captured in hydrological models for accurate water quantity and quality predictions and estimation of the hydrologic sensitivity of the land to change 38,39 , but they generally lack the skill to gather and interpret soil information 40,41 .…”

Soil Indicators of Hillslope Hydrology

“…Three major flow pathways exist in a typical hillslope: overland flow, subsurface lateral flow and bedrock flow (Karvonen et al 1999;Ticehurst et al, 2007). Subsurface lateral flow can be divided into: subsurface macropore flow, subsurface lateral flow at A-B horizon interface, return flow at the footslope and toeslope and flow at the soil-bedrock interface (Lin et al, 2006).…”

“…Ideally these hydrological models can best be developed using measurements of the surface and subsurface lateral flow paths, water table fluctuations, connectivity of the various water bodies and the residence flow time of water through the landscape. The landscape unit that is of particular importance is the hillslope (Karvonen et al, 1999;Lin et al, 2006;Ticehurst et al, 2007), hence the accent here on this landscape unit. The measurements named are however expensive and time consuming since these processes are dynamic in nature with strong temporal and spatial variation (McDonnell et al, 2007;Park & Van de Giesen, 2004;Ticehurst et al, 2007).…”

“…The landscape unit that is of particular importance is the hillslope (Karvonen et al, 1999;Lin et al, 2006;Ticehurst et al, 2007), hence the accent here on this landscape unit. The measurements named are however expensive and time consuming since these processes are dynamic in nature with strong temporal and spatial variation (McDonnell et al, 2007;Park & Van de Giesen, 2004;Ticehurst et al, 2007). The need for predictions of the named hydrological processes is becoming increasingly important and led to the launch an International Association of Hydrological Sciences (IAHS) initiative called Predictions in Ungauged Basins or PUB (Sivapalan 2003;Sivapalan et al, 2003) encouraging researchers and modellers to focus their efforts on predicting the hydrological behaviour of catchments based on physical principles without relying on calibrations of hydrological models.…”

Creating a conceptual hydrological soil response map for the Stevenson Hamilton Research Supersite, Kruger National Park, South Africa

“…Thus soil properties contain unique signatures of the hydrological regime under which they formed. Concepts developed about the soil water regime by field observations and quantification (Van Tol et al, 2011) make it possible to predict the conceptual response of different soil forms (Ticehurst et al, 2007;Van Tol et al, 2010;Kuenene et al, 2011). A soil map can be the basis to provide both the size and position of conceptual hydrological soil responses (CHSR's).…”