Integrated hydrogeological modelling of hard-rock semi-arid terrain: supporting sustainable agricultural groundwater use in Hout catchment, Limpopo Province, South Africa

Abstract

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.

Hydrochemical characterization of shallow and deep groundwater in Basement Complex areas of southern Kebbi State, Sokoto Basin, Nigeria

“…However, groundwater has been studied using different techniques: geothermal techniques (Nwankwo 2015;Nwankwo and Shehu 2015;Olatunji and Musa 2013;Toyin et al 2016), isotope techniques (Adelana et al 2003;Geyh and Wirth 1980;Fillion et al 2014Fillion et al , 2018Selck et al 2018;Kattan 2018;Alemayehu et al 2019;Besser et al 2019), multivariate statistics (Mondal et al 2010;Azhar et al 2015;Yidana et al 2018), univariate statistics (Marghade et al 2010;Selvakumar et al 2017;Wali et al 2018a, b), modeling (Ebrahim et al 2019;Locatelli et al 2019), and chemical indices (Marghade et al 2010;Panaskar et al 2016;Wagh et al 2016). Results obtained from these studies showed groundwater quality is influenced by both the natural geogenic processes and anthropogenic activities.…”

Diamonds on the Soles of Their Feet: Groundwater Monitoring in the Hout Catchment, South Africa

“…The complexity of the hydrological cycle, especially in these arid areas with highly variable and event-based rainfall, contrasts strongly with poor data availability, limiting the number of techniques and methods available to researchers and the accuracy of models and predictions (Ebrahim et al, 2019). Our aim was to gather reliable data and to develop a community of practice in the catchment.…”

Navigating wicked water governance in the “solutionscape” of science, policy, practice, and participation

“…Some farmers interviewed felt there was no problem, while others were increasingly worried about increasingly frequent drought events and depleting water levels. Meanwhile, recent modeling suggests a more cyclical and dynamic nature of the aquifer's recharge, rather than straightforward overabstraction (Ebrahim et al 2019). However, increasing climate variability and more frequent drought events may make recharge dynamics more difficult to discern.…”

“…First, considering the science and research dimension, there has historically been high uncertainty regarding the aquifer's physical status, though this is slowly improving because of recent hydrogeological modeling (Ebrahim et al 2019). However, data scarcity remains; long-term groundwater level observations are limited because of a degraded monitoring network, as are some issues of data sharing because of distrust between commercial farmers and the government.…”

“…Research regarding the groundwater status of the catchment has been carried out on and off for the past few decades, although there is little evidence of significant change in groundwater-use due to these studies. More recent research has been focused on groundwater modelling (by the International Water Management Institute) due to low groundwater data availability (most groundwater level recordings do not go back far enough to provide a clear picture of the aquifer's status) (Ebrahim et al 2019). This work has been carried out alongside contact with some commercial farmers, with interest paid to local knowledge of the environment.…”