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

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dc.contributor.authorWatson, Andrewen_ZA
dc.contributor.authorMiller, Jodieen_ZA
dc.contributor.authorFink, Manfreden_ZA
dc.contributor.authorKralisch, Svenen_ZA
dc.contributor.authorFleischer, Melanieen_ZA
dc.contributor.authorDe Clercq, Willemen_ZA
dc.date.accessioned2019-06-26T07:16:24Z
dc.date.available2019-06-26T07:16:24Z
dc.date.issued2019-06-24
dc.descriptionCITATION: Watson, A., et al. 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):2679-2697, doi:10.5194/hess-23-2679-2019.en_ZA
dc.descriptionThe original publication is available at https://www.hydrol-earth-syst-sci.neten_ZA
dc.description.abstractRiver 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.en_ZA
dc.description.urihttps://www.hydrol-earth-syst-sci.net/23/2679/2019/
dc.description.versionPublisher's versionen_ZA
dc.format.extent19 pages : illustrations, mapsen_ZA
dc.identifier.citationWatson, A., et al. 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):2679-2697, doi:10.5194/hess-23-2679-2019en_ZA
dc.identifier.issn1607-7938 (online)
dc.identifier.issn1027-5606 (print)
dc.identifier.otherdoi:10.5194/hess-23-2679-2019
dc.identifier.urihttp://hdl.handle.net/10019.1/106302
dc.language.isoen_ZAen_ZA
dc.publisherEuropean Geosciences Unionen_ZA
dc.rights.holderAuthors retain copyrighten_ZA
dc.subjectRiver ecosystemsen_ZA
dc.subjectGroundwater components distributionen_ZA
dc.subjectRainfall–runoff modellingen_ZA
dc.subjectEstuarine lakes -- Verlorevlei (South Africa)en_ZA
dc.titleDistributive 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 Africaen_ZA
dc.typeArticleen_ZA
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