Definition of soil water dynamics by combining hydrometry and geophysics in a hillslope transect in the KNP.
Loading...
Date
2006
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The budgeting of water fluxes in the soil is an extremely complex problem, and is
compounded by subsurface controls and environmental forces which modify the soil water
dynamics. Of the controlling factors, the underlying geology and the soil media are vital
components and are often misinterpreted. The geology and soil media components have been
neglected mostly because of the difficulty in monitoring the dominant processes that are
linked to the water balance in the subsurface. Until recently, hydrometry has been the
dominant method of measuring and monitoring the subsurface water balance. Hydrometric
measurements have included water content measurement by Time Domain Reflectometry
(TDR), soil water potential measurements through tensiometry and groundwater water level
monitoring. Hydrometry is still the preferred method of monitoring soil water dynamics, but
measurements are generally localised and lateral accumulations and fluxes of water are
difficult to interpret.
Using geophysical methods and instrumentation to define soil water dynamics could have
numerous advantages over conventional hydrometric methods. Among the geophysical
techniques dedicated to image the near surface, Electrical Resistivity Tomography (ERT)
surveying has been increasingly used for environmental, engineering and geological purposes
during the last decade. The aim of this study is to determine if ERT observations could yield
the accuracy required to define vertical and lateral soil water dynamics.
The ERT instrumentation uses an electrical current that is inserted into the subsurface through
various electrode arrangements and a resulting resistance is determined at the take-out
electrodes. With the aid of a modelling package these resistance values are reproduced into a
pseudosection of underlying resistivity distribution which is influenced by the moisture
conditions of the subsurface medium. This geophysical method is primarily used for
geological studies but by doing repeated surveys with the same electrode positioning,
moisture fluctuation monitoring could be realised.
Use of the ERT technique is at the forefront of soil water dynamics monitoring. The main
objective of this study is to propose that the ERT instrumentation could be a more efficient
and more informative method of studying soil water dynamics than the traditional soil water dynamics monitoring equipment, particularly to define lateral fluxes and accumulation of
subsurface water. The study site is a well instrumented transect in the Nkuhlu Exclosures in
the Kruger National Park, South Africa, where ongoing soil water dynamics are monitored.
The project aims to compare the ERT data to fiR data on a daily basis, over a period of three
weeks, during the rain season, monitoring event based wetting and the subsequent drying
phases of the soils in a 2-dimensional section.
The project and its fmdings are shown to be valuable to the hydrological interpretation of the
subsurface water balance. The application is shown to be particularly important to
ecohydrology, in the monitoring of soil water dynamics in a 2-dimensional transect and
understanding how the natural cycles of water distribution and plant uptake are linked
together. The study demonstrates that ERT can be used to observe changes in the water
storage and lateral fluxes within a transect which supports varying vegetation and ecologies.
The linking of water fluxes in the hydrology cycle to uptakes and controls in the ecosystem
has been developed into the research focus known as ecohydrology The use of the ERT
instrument can only benefit this research focus in the future. The study demonstrates that ERT
instrumentation can be used to provide valuable understanding of subsurface water dynamics
and in turn the effects on ecohydrology.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
Keywords
Ecohydrology., Plant-water relationships., Groundwater-data processing., Soil dynamics--Data processing., Hydraulic measurements., Theses--Bioresources engineering and environmental hydrology.