Modelling and water yield assessment of Lake Sibhayi

Article


Smithers, J. C., Gray, R. P., Johnson, S. and Still, D.. 2017. "Modelling and water yield assessment of Lake Sibhayi." Water SA. 43 (3), pp. 480-491. https://doi.org/10.4314/wsa.v43i3.13
Article Title

Modelling and water yield assessment of Lake Sibhayi

ERA Journal ID4309
Article CategoryArticle
AuthorsSmithers, J. C. (Author), Gray, R. P. (Author), Johnson, S. (Author) and Still, D. (Author)
Journal TitleWater SA
Journal Citation43 (3), pp. 480-491
Number of Pages12
Year2017
Place of PublicationSouth Africa
ISSN0378-4738
1816-7950
Digital Object Identifier (DOI)https://doi.org/10.4314/wsa.v43i3.13
Web Address (URL)https://www.ajol.info/index.php/wsa/article/view/159664
Abstract

This study has been undertaken to establish the probable causes of the almost 4 m drop in the level of Lake Sibhayi between 2001 and 2014, to assess the impact of abstractions for domestic water consumption and by commercial plantations on lake levels, and to determine what sustainable yield can be abstracted from Lake Sibhayi. From the analysis and simulations undertaken, it is concluded that the major cause of the drop in the level of Lake Sibhayi was the below-average rainfall over the period 2001 to 2011. However, while the simulation results show that the effect on lake levels of abstractions for domestic usage over this period has been negligible, they do indicate that nearly 1.4 m of the drop in lake level can be attributed to the impact of the afforestation which began in the catchment in the 1990s. A yield analysis of simulated results with historical developments in the catchment for the 65-year period of observed climate record was undertaken using both a fixed minimum allowable lake level or a maximum drop from a reference lake level as criteria for system failure. Results from simulating lake levels using the historical climate record with the area afforested and abstractions levels fixed at 2014 values indicate that no sustainable additional yield is possible because of the sustained decline in both the simulated lake levels and conceptual groundwater store, which would be environmentally, socially and ecologically unacceptable. Preliminary simulated results indicate that the removal of approximately 5 km2 of forestry is required to release 1 MCM/yr for domestic abstractions. However, these preliminary results require improved verification of input data and a review of the modelling for increased confidence in the results.

Keywordshydrology of Lake Sibhayi, lake level, abstractions, afforestation and yield
ANZSRC Field of Research 2020400513. Water resources engineering
410404. Environmental management
410402. Environmental assessment and monitoring
Institution of OriginUniversity of Southern Queensland
Byline AffiliationsNational Centre for Engineering in Agriculture
JG Afrika, South Africa
Partners in Development, South Africa
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