Malawi Hydrogeological and Water Quality Mapping: National Scale Recharge Estimation

Scheidegger, J.; Lafare, A.; Mansour, M.M.. 2015 Malawi Hydrogeological and Water Quality Mapping: National Scale Recharge Estimation. Nottingham, UK, British Geological Survey, 79pp. (CR/15/061N) (Unpublished)

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A toolbox of different recharge values and a distributed recharge model have been applied to estimate the recharge values over Malawi. The toolbox is prepared within Microsoft Excel and coded using Visual Basics. The distributed recharge calculation is undertaken using the BGS ZOODRM model. The model uses gridded daily rainfall and potential evaporation data as well as gridded landuse, topography, soil, and river data to calculate recharge. The distributed recharge model is calibrated by matching the simulated overland flows to the observed ones at selected gauging stations. However, difficulties were encountered during the calibration of the recharge model due to: (i) the resolution of the model grid being relatively coarse so that the topographical characteristics could not be fully captured, (ii) the number of runoff zones specified in the model not being enough to represent the characteristics of the study area, and (iii) there being a need to improve the representation of land cover in the model since the land cover affects the estimated recharge values. The estimated recharge values presented in this study are highly affected by the quality of data used in the distributed recharge model. Comparing the recharge values estimated from the recharge model and averaged over the district areas to the recharge values calculated using the recharge toolbox, it was clear that the former agree with the values of at least one analytical method included in the toolbox. However, there was no consistency of agreement, i.e. the recharge values produced by the distributed model did not agree with one particular method. The sensitivity analysis results indicate that the recharge values are highly affected by the soil type parameter values specified in the model and by the definition of spatial distribution of land cover. To improve the accuracy of recharge calculations using the distributed recharge model, it is recommended that maps with a better representation of these features are included in the model. In addition, further model calibration runs are needed to improve the quality of the estimated recharge values. This can be only achieved by obtaining better field data.

Item Type: Publication - Report
Funders/Sponsors: Council for Geoscience, British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed. Item made open by author in May 2019.
NORA Subject Terms: Hydrology
Date made live: 10 May 2019 09:09 +0 (UTC)

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