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1 Watson, A.; Miller, J.; Fleischer, M.; de Clercq, W. 2018. Estimation of groundwater recharge via percolation outputs from a rainfall/runoff model for the Verlorenvlei estuarine system, west coast, South Africa. Journal of Hydrology, 558:238-254. [doi: https://doi.org/10.1016/j.jhydrol.2018.01.028]
Groundwater recharge ; Rainfall-runoff relationships ; Models ; Percolation ; Coastal area ; Brackishwater environment ; Aquifers ; Groundwater table ; Water levels ; Catchment areas ; Soil types ; Evaporation ; Evapotranspiration ; Sensitivity analysis / South Africa / Verlorenvlei Estuarine Lake
(Location: IWMI HQ Call no: e-copy only Record No: H048590)
(3.76 MB)
Wetlands are conservation priorities worldwide, due to their high biodiversity and productivity, but are under threat from agricultural and climate change stresses. To improve the water management practices and resource allocation in these complex systems, a modelling approach has been developed to estimate potential recharge for data poor catchments using rainfall data and basic assumptions regarding soil and aquifer properties. The Verlorenvlei estuarine lake (RAMSAR #525) on the west coast of South Africa is a data poor catchment where rainfall records have been supplemented with farmer’s rainfall records. The catchment has multiple competing users. To determine the ecological reserve for the wetlands, the spatial and temporal distribution of recharge had to be well constrained using the J2000 rainfall/runoff model. The majority of rainfall occurs in the mountains (±650 mm/yr) and considerably less in the valley (±280 mm/yr). Percolation was modelled as 3.6% of rainfall in the driest parts of the catchment, 10% of rainfall in the moderately wet parts of the catchment and 8.4% but up to 28.9% of rainfall in the wettest parts of the catchment. The model results are representative of rainfall and water level measurements in the catchment, and compare well with water table fluctuation technique, although estimates are dissimilar to previous estimates within the catchment. This is most likely due to the daily timestep nature of the model, in comparison to other yearly average methods. These results go some way in understanding the fact that although most semi-arid catchments have very low yearly recharge estimates, they are still capable of sustaining high biodiversity levels. This demonstrates the importance of incorporating shorter term recharge event modeling for improving recharge estimates.
2 Addo, K. A.; Brempong, E. K.; Jayson-Quashigah, P. N. 2020. Assessment of the dynamics of the Volta River Estuary shorelines in Ghana. Geoenvironmental Disasters, 7:19. [doi: https://doi.org/10.1186/s40677-020-00151-1]
Rivers ; Estuaries ; Coastal erosion ; Brackishwater environment ; Disaster risk reduction ; Vulnerability ; Assessment ; Sediment ; Flooding ; Climate change ; Communities / Ghana / Volta River Estuary / Volta Delta / Akosombo Dam
(Location: IWMI HQ Call no: e-copy only Record No: H049778)
https://geoenvironmental-disasters.springeropen.com/track/pdf/10.1186/s40677-020-00151-1
https://vlibrary.iwmi.org/pdf/H049778.pdf
https://vlibrary.iwmi.org/pdf/H049778.pdf
(1.66 MB) (1.66 MB)
Estuarine shorelines similar to marine coastlines are highly dynamic and may increase disaster risk in vulnerable communities. The situation is expected to worsen with climate change impacts and increasing anthropogenic activities such as upstream water management. This study assessed shoreline changing trends along the Volta river estuary in Ghana as well as the marine coastline using satellite imageries, orthophotos and topographic maps spanning a period of 120 years (1895, 1990, 2000, 2005 and 2015). Linear regression method in the Digital Shoreline Analysis System (DSAS) was used to determine the estuary shoreline migration trend by estimating the shorelines rate of change for the eastern and western sides of the estuary. The rates of change of the marine coastlines on the east and west of the estuary were also estimated. The results show that the eastern and western shoreline of the estuary are eroding at an average rate of about 1.94 m/yr and 0.58 m/yr respectively. The coastlines on the marine side (eastern and western) are eroding at an average rate of about 2.19 m/yr and 0.62 m/yr respectively. Relatively high rates of erosion observed on the eastern estuarine shoreline as well as the coastline could be explained by the reduced sediment supply by the Volta River due to the damming of the Volta River in Akosombo and the sea defence structures constructed to manage erosion problems. The trend is expected to increase under changing oceanographic conditions and increased subsidence in the Volta delta. Effective management approach, such as developing disaster risk reduction strategy, should be adopted to increase the resilience of the communities along the estuarine shoreline and increase their adaptive capacity to climate change hazards and disasters.
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