Dams hold numerous benefits for society through their ability to store water on a long-term basis.
However, it is well-known that there is a detrimental effect of dams on the rivers that they
impound, and this has been taken into account by the South African National Water Act (1998).
The Act specifies a two component Reserve to provide a basic water supply to humans and to
provide protection to downstream rivers and their associated ecosystems. From an ecological
perspective, emphasis is now placed on ensuring that flow in rivers is maintained in a state that
closely mimics the natural flow regime in order to sustain the water resource and its associated
aquatic ecosystems. The resulting challenge for water resources modelling is to develop operating
rule frameworks that can account for water supply to multiple users, including the "environment"
which represents downstream aquatic ecosystems. These frameworks need to consider both water
stored in dams, as well as water in the river which has been allocated to different water uscrs.
Such an operating rule framework has been implemented ID the daily time-step ACRU
agrohydrological model in order to:
(a) satisfy the requirements of water users in general,
(b)
(c)
include the environment as a user of water, and thus
attempt to satisfy the water requirements of rivers and their associated ecosystems by
making artificial releases from dams using both a simple and a complicated approach for
determining the environmental requirements.
The framework identifies four types of water users, each of which are capable of requesting water
from a water source. These users are: a domestic user, representing the basic human needs
component of the Reserve, an environmental user, representing the ecological component of the
Reserve, an industrial user and an irrigator. The environmental user can generate water requests
using either a simple or a complex environmental request method. The simple approach has proved
to be oversimplified while the complex approach is capable of producing a flow regime
downstream of a dam that closely mimics the natural flow regime.
Two operating rules are employed to supply water to the four users, a generic dam operating rule,
which considers water requested from a dam, and a channel operating rule, which considers water requested from a river. The two operating rules determine the amounts of water that each user can
receive through the use of a curtailment structure, where abstractions made by users are limited,
based on the storage level in the dam.
Extensive validation of the framework has taken place and a case study was undertaken on the
Pongola-Bivane river system which includes the Paris Dam in order to run various real-life
scenarios. The results obtained show not only that the operating rule framework is functioning
correctly, but that the use of a curtailment structure holds advantages for increasing assurance
levels of the water users. There is also evidence to suggest that future possibilities exist for
practical application of the operating rule framework to "everyday" dam operations. / Thesis (M.Sc.)-University of Natal,Pietermaritzburg, 2001.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5599 |
| Date | January 2001 |
| Creators | Butler, Andrew John Edward. |
| Contributors | Smithers, Jeffrey Colin., Jewitt, Graham Paul Wyndham. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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