Calibration, validation and application of the SWAT model to determine the hydrological benefit of wetland rehabilitation in KwaZulu-Natal, South Africa

In South Africa, with highly variable and intense land-use practices, coupled with limited soil fertility and water resources, there has been a long history of encroachment of arable lands (sugarcane and timber plantations) into surrounding wetlands. Although wetland delineation within the timber an...

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Bibliographic Details
Published in:Water S. A. 2022-10, Vol.48 (4), p.348-358
Main Authors: Scott-Shaw, Bc, Lechmere-Oertel, R, Hill, Tr
Format: Article
Language:English
Subjects:
Aquatic resources
Biodiversity
Buffers
Calibration
Climate
Commercial species
Continuous time systems
Evaporation
Hydrologic cycle
Hydrological cycle
Hydrology
Land use
Land use management
Legislation
Moisture content
Nonpoint source pollution
Point source pollution
Pollution sources
Precipitation
Rehabilitation
Resource management
Return flow
River basins
Rivers
Runoff
Soil
Soil moisture
Soil water
South Africa
Stream discharge
Stream flow
Streamflow
Sugarcane
Surface runoff
Timber
Vadose water
Water balance
Water content
Water pollution
Water resources
Water resources management
Water supply
Water use
Watersheds
Wetland conservation
Wetlands
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Summary:In South Africa, with highly variable and intense land-use practices, coupled with limited soil fertility and water resources, there has been a long history of encroachment of arable lands (sugarcane and timber plantations) into surrounding wetlands. Although wetland delineation within the timber and sugar sectors is well-defined in policy, and existing and proposed legislation, there are significant areas of non-compliance. The spatially-explicit Soil Water Assessment Tool (SWAT) was adopted to investigate the interactions of climate, land-use and soil on the water-use of natural and encroached wetlands. This paper documents the calibration, validation and application of the SWAT model on Quaternary Catchment (QC) U20G, which is a 498 [km.sup.2] catchment that forms part of the uMngeni River basin. The SWAT-CUP parameter sensitivity and optimization model was tested with daily observed streamflow data for this catchment. Parameters were modified using the sequential uncertainty fitting (SUFI-2) analysis routine to calibrate the model. The simulated flow had a close fit to the observed flow with a regression coefficient ([r.sup.2]) of 0.87 and a Nash-Sutcliffe (NS) coefficient of 0.8. Through the buffer scenario analysis, the model showed that if the wetland and a 20-m buffer were to be returned to a natural state, there could be a 16% increase in the annual streamflow contribution, with an upper limit of a 60% increase in some hydrologic response units (HRUs).Thus there would be a hydrological gain if wetlands and sensitive buffer areas were to be cleared of commercial timber species and sugarcane. KEYWORDS SWAT modelling calibration stream flow reduction commercial plantations sugarcane
ISSN:0378-4738
DOI:10.17159/wsa/2022.v4S.i4.3857