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Distributive rainfall-runoff modelling to understand runoff-to-baseflow proportioning and its impact on the determination of reserve requirements of the Verlorenvlei estuarine lake, west coast, South Africa

Watson, Andrew and Miller, Jodie and Fink, Manfred and Kralisch, Sven and Fleischer, Melanie and de Clercq, Willem (2019) Distributive rainfall-runoff modelling to understand runoff-to-baseflow proportioning and its impact on the determination of reserve requirements of the Verlorenvlei estuarine lake, west coast, South Africa. Hydrology and Earth System Sciences, 23 (6), pp. 2679-2697. Copernicus Publications. DOI: 10.5194/hess-23-2679-2019 ISSN 1027-5606

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Official URL: https://www.hydrol-earth-syst-sci.net/23/2679/2019/

Abstract

River systems that support high biodiversity profiles are conservation priorities worldwide. Understanding river ecosystem thresholds to low-flow conditions is important for the conservation of these systems. While climatic variations are likely to impact the streamflow variability of many river courses into the future, understanding specific river flow dynamics with regard to streamflow variability and aquifer baseflow contributions is central to the implementation of protection strategies. While streamflow is a measurable quantity, baseflow has to be estimated or calculated through the incorporation of hydrogeological variables. In this study, the groundwater components within the J2000 rainfall–runoff model were distributed to provide daily baseflow and streamflow estimates needed for reserve determination. The modelling approach was applied to the RAMSAR-listed Verlorenvlei estuarine lake system on the west coast of South Africa, which is under threat due to agricultural expansion and climatic fluctuations. The sub-catchment consists of four main tributaries, Krom Antonies, Hol, Bergvallei and Kruismans. Of these, Krom Antonies was initially presumed the largest baseflow contributor, but was shown to have significant streamflow variability attributed to the highly conductive nature of the Table Mountain Group sandstones and Quaternary sediments. Instead, Bergvallei was identified as the major contributor of baseflow. Hol was the least susceptible to streamflow fluctuations due to the higher baseflow proportion (56%) as well as the dominance of less conductive Malmesbury shales that underlie it. The estimated flow exceedance probabilities indicated that during the 2008–2017 wet cycle average lake inflows exceeded the average evaporation demand, although yearly rainfall is twice as variable in comparison to the first wet cycle between 1987 and 1996. During the 1997–2007 dry cycle, average lake inflows are exceeded 85% of the time by the evaporation demand. The exceedance probabilities estimated here suggest that inflows from the four main tributaries are not enough to support Verlorenvlei, with the evaporation demand of the entire lake being met only 35% of the time. This highlights the importance of low-occurrence events for filling up Verlorenvlei, allowing for regeneration of lake-supported ecosystems. As climate change drives increased temperatures and rainfall variability, the length of dry cycles is likely to increase into the future and result in the lake drying up more frequently. For this reason, it is important to ensure that water resources are not over-allocated during wet cycles, hindering ecosystem regeneration and prolonging the length of these dry cycle conditions.

Item URL in elib:https://elib.dlr.de/128475/
Document Type:Article
Title:Distributive rainfall-runoff modelling to understand runoff-to-baseflow proportioning and its impact on the determination of reserve requirements of the Verlorenvlei estuarine lake, west coast, South Africa
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Watson, AndrewDepartment of Earth Sciences, Stellenbosch UniversityUNSPECIFIED
Miller, JodieDepartment of Earth Sciences, Stellenbosch UniversityUNSPECIFIED
Fink, ManfredDepartment of Geoinformatics, Friedrich Schiller University JenaUNSPECIFIED
Kralisch, SvenGerman Aerospace Center (DLR), Institute of Data ScienceUNSPECIFIED
Fleischer, MelanieDepartment of Geoinformatics, Friedrich Schiller University JenaUNSPECIFIED
de Clercq, WillemStellenbosch Water Institute, Stellenbosch UniversityUNSPECIFIED
Date:24 June 2019
Journal or Publication Title:Hydrology and Earth System Sciences
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:23
DOI :10.5194/hess-23-2679-2019
Page Range:pp. 2679-2697
Publisher:Copernicus Publications
ISSN:1027-5606
Status:Published
Keywords:rainfall–runoff modelling, river ecosystem, low-flow, baseflow, water resources
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:other
DLR - Research area:Raumfahrt
DLR - Program:R - no assignment
DLR - Research theme (Project):R - no assignment
Location: Jena
Institutes and Institutions:Institute of Data Science
Deposited By: Kralisch, Sven
Deposited On:28 Aug 2019 11:59
Last Modified:28 Aug 2019 11:59

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