Rigorous Methodology For Sustainable Yield Estimation Using Groundwater Numerical Modelling Validation To Detailed Long Term Pumping Test Data

Groundwater numerical models are commonly used to determine the impact that groundwater abstraction has on the ability of surrounding areas to supply water, and thus to inform Water Use Licence (WUL) Applications. However, data available is often limited to that generated by relatively short-term geohydrological studies and pumping tests. In most cases this data and the degree of defined uncertainty in the model results are sufficient. However, for large scale abstractions (such as municipal abstraction) and in sensitive or complex geological areas, a more rigorous approach to calculating the impact from pumping is recommendable. The study area is located on a syncline consisting of two sandstone aquifers. However, there was a lack of data to quantify the connectivity between the two aquifers. SRK Consulting (South Africa) (Pty) Ltd undertook a rigorous, long-term approach, which included a 3- year monitoring plan of the area, input from stakeholders, extending the hydrocensus to the entire catchment and monitoring of pumping in the area. Using this comprehensive data set, the existing numerical groundwater model was updated, re-calibrated and validated such that predictive scenarios could be run to assess the long-term potential impact of the municipal wellfield. These results were submitted for the final allocation of the WUL. Along with mitigation measures, recommendations could also be made on where to focus monitoring and future testing. This rigorous methodology and the use of long- term comprehensive monitoring data is recommended for future use in similarly complex environments to decrease uncertainty on the expected impacted area from large-scale abstractions.

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Port Alfred
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