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Testing a Methodology for Environmental Water Requirements in Non-perennial Rivers: The Mokolo River Case Study
Expanded Title:This research has contributed considerably to the knowledge of the ecological functioning of non-perennial rivers and the testing of a method to determine the Environmental Water Requirements (EWRs) for non-perennial rivers. This report should be read in conjunction with the WRC report no TT459/10 (Seaman et al., 2010) where the ecological functioning of non-perennial rivers and the prototype methodology is explained. Research into the development of a non-perennial Environmental Water Requirements (EWR) method started in 2005 using the Seekoei River (a non-perennial southern tributary of the Orange River) as a case study (Seaman et al., 2010). Results showed that the interaction between groundwater and surface water is of critical importance in non-perennial rivers, (probably also in perennial rivers), and that the methods used to determine the EWR should take this into consideration. It was further found that the existing standard hydrological models are inadequate for describing and predicting the hydrology of the full spectrum of non-perennial rivers (episodic to semi-permanent). Licenses for the abstraction or release of water in these rivers would therefore have to be based on a specific understanding of the ecology of non-perennial rivers and a hydrological model that can address surface and groundwater interaction. The DRIFT-Arid method developed in these projects is based on DRIFT (Downstream Response to Imposed Flow Transformations; Brown et al., 2008) (TT 575/13). This report indicates that the DRIFT-Arid method was applied with success in the semi-permanent Mokolo River. It is now recommended that this model be tested on an episodic river to verify its applicability for use on a range of non-perennial rivers. Hydrology is one of the main drivers of DRIFT-Arid method and the importance of groundwater in non-perennial rivers is emphasised. A first attempt at using an integrated surface and groundwater hydrology model (MIKE SHE) was included in the current project. An important output has been the identification of data gaps and the implications of this for reliable modelling, as well as the sensitivity of the integrated model to vegetation (especially riparian vegetation characteristics), subsurface and soil data. A need exists for further studies in these disciplines. It is evident that monthly flow data were insufficient to capture the variability of flow in non-perennial rivers and that daily flow data should be used for hydrological modelling In systems with sparse data, the modeller could use climate data as a surrogate for gauge data. A recurring theme in all projects where hydrology is modelled is the lack of accurate data. This needs to be addressed and in South Africa where functioning gauging weirs are scarce alternative methods need to be developed to collect data on flow.
Date Published:01/11/2013
Document Type:Research Report
Document Subjects:Water Resource Management/IWRM - Planning and development, Ecosystem - Biodiversity protection
Document Format:Report
Document File Type:pdf
Research Report Type:Technical
WRC Report No:TT 579/13
ISBN No:978-1-43120-485-4
Authors:Seaman MT; Watson M; Avenant MF; Joubert AR; King JM; Barker CH; Esterhuyse S; Graham D; le Roux PA; Prucha B; Redelinghuys N; Rossouw L; Rowntree K; Sokolic F; Van Rensburg L; an der Waal B; Van Tol J; Vos AT; Kemp ME
Project No:K5/798
Originator:WRC
Organizations:University of the Free State
Document Size:10 760 KB
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