An integrated hydrogeological modelling approach applicable to hard-rock aquifers in semi-arid data-scarce Africa was developed using remote sensing, rainfall-runoff modelling, and a three-dimensional (3D) dynamic model. The integrated modelling approach was applied to the Hout catchment, Limpopo Province, South Africa, an important agricultural region where groundwater abstraction for irrigation doubled during 1968-1986. Since the 1960s, groundwater levels in irrigated areas have displayed extended periods of decline with partial or full recovery in response to major decadal rainfall events or periods. The integrated dynamic 3D hydrogeological flow model, based on the One-Water Hydrologic Flow Model (MODFLOW-OWHM), helped to understand recharge and flow processes and inform water use and management. Irrigation abstraction was estimated based on irrigated crop area delineated using the Landsat Normalized Difference Vegetation Index (NDVI) and crop water requirements. Using groundwater level data, the model was calibrated (2008-2012) and validated (2013-2015). Estimated mean diffuse recharge (3.3 ± 2.5% of annual rainfall) compared well with estimates from the Precipitation Runoff Modelling System model. Recharge and groundwater storage showed significant inter-annual variability. The ephemeral river was found to be losing, with mean net flux to the aquifer (focused recharge) of~1.1% of annual rainfall. The results indicate a delicate human-natural system reliant on the small but highly variable recharge, propagating through variable pumping to an even more variable storage, making the combined system vulnerable to climate and anthropogenic changes. The integrated modelling is fundamental for understanding spatio-temporal variability in key parameters required for managing the groundwater resource sustainably.
A field experiment was carried out to study the effect of drain depth on the drainage water quality and flax productivity. The flax crop was planted during winter season. The field experiment was conducted at the Bahteem Research Station, Qaliubiya Governorate, from November 2015 till April 2016. Two design systems were selected, the first was conventional drainage system (CDS), with drain depth 1.5 m, the second was modified drainage system (MDS), three lateral drain lines were installed to main drain directly. The depth of the lateral drain was (0.90-1.0) m. The obtained results revealed that the salinity of the average soil profile decreased after the second irrigation onward. The soil salinity percentages of (MDS) decreased by (47, 30 and 9.5) for (2 nd , 3 rd and 4 th) irrigation, respectively. On the other hand, soil salinity percentages of (CDS) decreased by (40, 32 and 9) for (2 nd , 3 rd and 4 th) irrigation, respectively. The chloride percentages for average soil profile of (MDS) decreased by (77, 82 and 54) for (2 nd , 3 rd and 4 th) irrigation, respectively. On the other hand, the chloride percentages of (CDS) decreased by (70, 75 and 35) for (2 nd , 3 rd and 4 th) irrigation, respectively. The EC values of drainage water of (MDS) decreased from first irrigation onwards. The EC percentages of drainage water salinity of (MDS) decreased by (10.6, 18.2 and 22.7) for (2 nd , 3 rd and 4 th) irrigation, respectively. On the other hand, the EC percentages of drainage water salinity of (CDS) decreased by (6.3, 5.6 and 24.6) for (2 nd , 3 rd and 4 th) irrigation, respectively. The chloride percentages of drainage water salinity of (MDS) decreased by (22.6, 43 and 14.2) for (2 nd , 3 rd and 4 th) irrigation, respectively. On the other hand, the chloride percentages of (CDS) decreased by (14.7, 32 and 16.4) for (2 nd , 3 rd and 4 th) irrigation, respectively. The piezometer reading showed that the water table levels reaching the soil surface upon irrigation reached low level before the next irrigation. The average values of water table after first irrigation were (14.5, 11 cm) for (MDS) and (29.5, 24 cm) for (CDS) for (L/4, L/2 distance from drain line), respectively. Also the results indicated that the water table level continue decreasing for both systems before 2 nd and 3 rd irrigation. The results recorded were (91, 82 cm), (140.5, 132 cm) before 2 nd irrigation; (75.5, 60 cm), (133.5, 125 cm) before 3 rd irrigation for (L/4, L/2 distance from drain line) for both systems (MDS) and (CDS), respectively. On the other hand data showed that the water table was higher after 2 nd irrigation on ward. The results recorded were (16.5, 10 cm), (33.5, 25 cm) after 2 nd irrigation; (7.5, 3 cm), (28, 21 cm) after 3 rd irrigation for (L/4, L/2 distance from drain line) for both systems (MDS) and (CDS) respectively. So (MDS) produced drainage water with higher quality and lower salts concentration than the (CDS). At the end of the season the flax productivity was 3.5 ton/fed for both systems. It can be recommended to be us...
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