Process and modelling studies in forest hydrology.
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Date
1995
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Abstract
The demand for timber products in South Africa, and consequently afforestation, is
increasing. There exists, however, abundant experimental evidence that trees utilise more
soil water than other dryland crops. Because water is limited in South Africa, decision
makers therefore currently face the challenge of determining a socially, and economically
acceptable afforestation management plan to enable the reconciliation of increased timber
demand with scarce water supply. This challenge, and the subsequent decisions that need
to be made, may be accomplished by making use of suitable simulation models to predict
the impacts of the forest hydrological system on water resources. Currently, these impacts
are assessed through an Afforestation Permit System (APS) which is based on a model now
acknowledged to have become outdated. In this dissertation an enhanced ACRU Forest
Decision Support System (FDSS), now called the ACRU Forest model, is developed and
proposed as a tool for modelling forest hydrological impacts on water resources.
Research for this study included a literature survey, fieldwork at two locations, viz. at
forest irrigation trials at Mkuze in northern KwaZulu-Natal, and at forest site preparation
trials near Ugie in the Eastern Cape, as well as the evaluation, for purposes of model
development, of a series of workshops. Results from the fieldwork experiments show that
large tree water use potentials are possible if water is not limiting, although a water supply
threshold exists at about 1400mm.annum-1, above which diminishing growth returns occur.
Furthermore, trees display improved growth on more intensive forest site preparations, but
at the expense of higher water usage rates. A series of workshops which had as the main
objective the extraction of expert knowledge by stimulating responses to prepared questions
and by constructive discussion on relative issues pertaining to forest hydrological
modelling, yielded valuable information. This information, together with that gleaned
from the literature, the fieldwork and a new Quaternary catchment database for South
Africa, was used to develop the ACRU Forest model.
The PC-based ACRU Forest model has the potential to aid decision makers by providing
an initial indication of the impacts of afforestation on water resources, within a matter of
minutes. An example of the model's application is used to demonstrate its operation,
relative accuracy and its potential benefits in simulating hydrological responses to
afforestation.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Hydrology, Forest--South Africa., Soil moisture--Mathematical models., Hydrology--Mathematical models., Theses--Bioresources engineering and environmental hydrology.