Developing a model to assess the impact of farm dams and irrigation for data-scarce catchments

ABSTRACT

Productive agricultural supply chains require the support of functional ecosystems, but intense agricultural practices change local hydrological systems (e.g. river diversion). In this study, the impact of farm dams was assessed for the Verlorenvlei catchment, a sensitive ecosystem currently under a state of hydrological change in South Africa. We developed a new module for the Jena Adaptable Modelling System (JAMS)/J2000 rainfall–runoff model to assess the streamflow impact from the points of abstraction, losses during storage and irrigation. The model achieved a satisfactory streamflow calibration with efficiencies Nash Sutcliffe Efficiency (NSE, logNSE) of 0.52 and 0.51. The irrigated area reduced simulated streamflow by 12 to 19%. The results from the study agree with remote sensed evapotranspiration, measured lake surface water levels and streamflow, but uncertainty remains in the total simulated dam evaporation. While many catchments lack the data required for a detailed irrigation impact assessment, this approach considers total water use, dam storage to area relationships and general farming practices.

KEYWORDS:

• Irrigation
• rainfall–runoff modelling
• JAMS/J2000
• hydrological change
• South Africa

Editor K. Soulis; Associate Editor S. Huang

Editor K. Soulis; Associate Editor S. Huang

Acknowledgements

The authors thank the WRC, SASSCAL and DWS for project funding as well as the NRF, Iphakade and DAAD (German Academic Exchange Service: sponsored by BMBF, The Federal Ministry of Education and Research) for bursary support. Furthermore, recognition is given to the Agricultural Research Council (ARC), South African Weather Service (SAWS), South African Earth Observation network (SAEON), the Department of Water Affairs and Sanitation (DWS) and Hortec (iLeaf) for access to hydroclimatic data. Monique and Frans Vlok provided information regarding irrigation scheduling. The authors thank the Associate Editor Shaochun Huang and two anonymous reviewers for their valuable comments and additions. The publisher is fully responsible for the content.

Disclosure statement

No potential conflict of interest was reported by the author(s).