Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in ... more Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in basin hydrology and overall ecosystem biogeochemistry. Thus, understanding soil erosion patterns in catchments is critical for conservation planning. This study was conducted in a peri-urban Inner Murchison Bay (IMB) catchment on the northern shores of Lake Victoria since most soil erosion studies in Sub-Saharan Africa have been focused on rural landscapes. The study sought to identify sediment sources by mapping erosion hotspots using the revised universal soil loss equation (RUSLE) model in appendage with field walks. RUSLE model was built in ArcGIS 10.5 software with factors including: rainfall erosivity, soil erodibility, slope length and steepness, land cover and support practices. The model was run, producing an erosion risk map and field assessments conducted to ground-truth findings and identify other hotspots. The percentage areas for RUSLE modelled erosion rates were: 66.8% for 0-2 t ha −1 year −1 ; 10.8% for 2-5 t ha −1 year −1 ; 10.1% for 5-10 t ha −1 year −1 ; 9% for 10-50 t ha −1 year −1 and 3.3% for 50-100 t ha −1 year −1. Average erosion risk was 7 t ha −1 year −1 and the total watershed erosion risk was 197,400 t year −1 , with croplands and steep areas (slope factor > 20) as the major hotspots (> 5 t ha −1 year −1). Field walks revealed exposed soils, marrum (gravel) roads and unlined drainage channels as other sediment sources. This study provided the first assessment of erosion risk in this peri-urban catchment, to serve as a basis for identifying mitigation priorities. It is recommended that tailored soil and water conservation measures be integrated into physical planning, focusing on identified non-conventional hotspots to ameliorate sediment pollution in Lake Victoria.
The main objective of this study was to examine the implications of watershed management (WSM) on... more The main objective of this study was to examine the implications of watershed management (WSM) on hydrological parameters in the Aba Gerima watershed in the Upper Blue Nile Basin. The Hydrus 1D model simulations were conducted in control sites and sites under WSM to estimate various components of the hydrologic cycle, using different soil physical & hydrological data under each category of experimental sites. Results were calibrated with measured soil moisture data through inverse solutions. Thus, Hydrus 1D model was found to be effective in predicting results, with R2 values of 0.73 to 0.853 and RMSE values ranging from 0.015 to 0.04. The cumulative evaporation estimated for 365 days for control sites was 37.6% higher than that of sites under WSM. Surface and bottom fluxes in the sites under WSM were 4.6% and 12.5%, respectively, higher than the control sites. This could be attributed to the increased soil water availability resulting from the implemented WSM practices in Aba Gerim...
<p><em>Study aim</em>: To test the performance of 7 glo... more <p><em>Study aim</em>: To test the performance of 7 global hydrological models against local South African datasets from the Earth2Observe platform in terms of the monthly water balance estimation.</p><p><em>Methodology:</em> The remotely-sensed global forcing datasets tested are actual evapotranspiration (ET) and runoff provided by Earth2Observe models. The local datasets were retrieved from the Water Resources of South Africa (WR2012) database, which quantifies the water resources of South Africa, Lesotho and Swaziland per quaternary catchment. The Quaternary Catchments consist of the lowest and most detailed level of operational catchment in the Department of Water and Sanitation (DWS), South Africa. An assessment of outputs between WR2012 and the ensemble outputs available to download from the seven Earth2Observe models (CEH, CNRS, UNIVK, UNIVU, METFR, JRC, and ECMWF) was conducted in South Africa. The mean annual runoff (MAR) time series analysis for the WR2012 and the Earth2Observe models were calculated. The Percentage of Bias (PoB) of each of the seven models with respect to the WR2012 data were computed as: %bias = (MAR<sub>i</sub> - MAR<sub>WR</sub>) x 100/ MAR<sub>WR.</sub></p><p><em>Results:</em> Models JRC, UNIVU, and CNRS showed excessive bias values in large areas while the remaining four models generally exhibited large negative bias values, but with high positive values in the extreme Northeast and the dry areas of the country. The wetter regions of the country (Eastern Cape and KwaZulu Natal) displayed consistent results across all models. Apart from CNRS, all the results have an approximate water balance (precipitation = evapotranspiration + runoff). This is largely due to compensating over or under estimation of both precipitation and evapotranspiration.</p><p><em>Conclusion and Recommendations:</em> The seven models are therefore rendered unreliable for water balance information in South Africa. Additionally, this study shows that ET data from the Earth2Observe platform is reliable to use, but the global runoff datasets should not be used in South Africa. It is recommended that organisations responsible for the generation of these global datasets issue warnings that these outputs have not been validated thus cannot be relied on.</p>
<p><strong></strong></p><p>... more <p><strong></strong></p><p><em>Background/aims</em></p><p>Water scarcity is a significant problem in South Africa. Low average rainfall results in limited water available for human and environmental needs. Consequently, competition for water resources is increasing and has resulted in water-related conflicts among the various water users in many areas of South Africa. Unfortunately, when competition for water use exists, Environmental Water Requirements (EWRs) are often ignored, thus impacting the health of riverine ecosystems and downstream ecosystem services. Such a situation characterises the Koue Bokkeveld farming region. Conflicts are rife between upstream farmers who have initial access to river water and downstream farmers forced to use what remains after upstream users satisfy their needs. The situation entrenches inequality and fuels conflict and, if left unmanaged, may lead to a breakdown in the farming community. The resultant loss in agricultural productivity will affect food security and the livelihood of the thousands of farmworkers who work in the area. This research project responds to this problem by negotiating a shared water management strategy that achieves equity in water access and respects EWR.  The broader aim is to assist Koue Bokkeveld (KBV) stakeholders in co-developing a water resources management strategy that results from a shared understanding.</p><p><em>Methodological framework</em></p><p>To achieve the research aim, a mixed methodological approach driven by Agent-Based Modelling is employed. A companion modelling approach is adopted, thus placing stakeholders at the centre of the model development and application. A series of stakeholder workshops are lined where stakeholders will provide input into and validate the model. Future scenarios (and subsequent impacts on an agreed water management plan) will be evaluated, assisted by hydrological modelling of future flows.</p><p><em>Preliminary results </em></p><p> An initial conceptual ABM model based on literature and an understanding of the study area representing the key actors, resources and dynamics obtained in the catchment has been developed. An initial stakeholder workshop to solicit stakeholder buy-in has been conducted with success. Although stakeholders remain sceptical about their identities and activities being kept in confidence-they are keen to participate in the following workshops.</p><p>Keywords: ABM, South Africa, stakeholder-engagement, water resources, modelling</p>
<p>Changing climate and expanding irrigated agriculture exert significant pressure ... more <p>Changing climate and expanding irrigated agriculture exert significant pressure on the already limited water resources in many regions of the world. This study is located in a South African strategic water source area called the Koue Bokkeveld (KBV). The area is characterised by a strongly seasonal flow regime, where winter flash flood flows dominate and long dry summer periods are experienced. Numerous small reservoirs have been constructed in the catchment to capture the extreme winter flows. The region is a biodiversity hotspot with a number of endemic species and forms part of the strategic water source area in South Africa (10% of South Africa’s land surface produces 80% of the country’s runoff).</p><p>During the long dry summer period, conflicts over water use and allocation among farmers in the study catchment emerge. When this happens, river flows are abstracted without considering ecological reserve (environmental flow) requirements.</p><p>This study quantifies the availability of water resources in the KBV catchment to contribute to creating an equitable and more sustainable water management plan that addresses water-related conflicts among farmers and ensures that ecological reserve requirements are met. SWAT+ has been set up for this study as it allows the representation of spatially distributed reservoirs and river diversion points within a catchment. This study also simulates future flow scenarios in the context of changing climate.</p><p>The outcomes of this project will be used to support decision-making regarding sustainable water management. This includes being used as input into an Agent-Based Model (ABM) that will be utilised to explore various management scenarios. Furthermore, the modelled current and future water availability information will assist catchment managers in making informed decisions about how water management could be adapted to changes in water availability.</p><p>The project is half way through, with SWAT setup complete. A meeting with the farmers in early 2022 will assist with further calibration of the model, in terms of reservoir and irrigation dynamics. The possibility of additional reservoirs will be explored to counter the run of river summer abstraction occurring that is currently negatively impacting the biodiversity.</p>
The Ecological Reserve (environmental flows) as defined under the South African National Water Ac... more The Ecological Reserve (environmental flows) as defined under the South African National Water Act 36 of 1998 was designed to equitably manage water for river sustainability while maximizing economic and social welfare. We investigated the climate change impacts on the Ecological Reserve targets for a seasonal river in an agricultural catchment in the Western Cape region using the Habitat Flow Stressor Response method (which integrates hydrology, hydraulics, water quality, and ecological data) under projected climate scenarios (2041–2070). Current Ecological Reserve model outcomes for 3 sites on the Doring River were compared with the future hydrology using Global Circulation Models associated with four Representative Concentration Pathways (RCP 2.6–8.5). Climate predictions reflected reduced future flows, but the uncertainty band of predicted future flows overlapped with present day flows. Flood flashiness following heavy rains and the increased length of dry periods that are predi...
To increase the resilience of regional water supply systems in South Africa in the face of antici... more To increase the resilience of regional water supply systems in South Africa in the face of anticipated climatic changes and a constant increase in water demand, water supply sources require diversification. Many water‐stressed metropolitan regions in South Africa depend largely on surface water to cover their water demand. While climatic and river discharge data is widely available in these regions, information on groundwater resources – which could support supply source diversification – is scarce. Groundwater recharge is a key parameter that is used to estimate groundwater amounts that can be sustainably exploited at a sub‐watershed level. Therefore, the objective of this study was to develop a reliable hydrological modelling routine that enables the assessment of regional spatio‐temporal variations of groundwater recharge to discern the most promising areas for groundwater development. Accordingly, we present a semi‐distributed hydrological modelling approach that incorporates wa...
Accurately quantifying actual evapotranspiration (ETa) over wetlands is important for the improve... more Accurately quantifying actual evapotranspiration (ETa) over wetlands is important for the improved management of these ecosystems, since 65% of them are threatened by clearing or drainage in South Africa. This study evaluated a range of available estimates of ETa over six palmiet wetlands, which are key ecological structures in terms of water regulation and sediment trapping. The research compared three remote sensing based products (a local product, FruitLook, and two global data products, MOD16 ET and EEFlux) across different rainfall years (2008 to 2019). Their outputs were validated, where possible, with limited ground-based scintillometer data on the Krom palmiet wetland, which indicated that MOD16 and EEFlux were most representative of ground-based measurements. We also compared the small pixel size EEFlux data over three wetlands with ETa over increasing buffers of land cover (100, 500, 1000 m) in order to validate the perception of these wetlands being high water users. Whil...
Drought occurrences in Rakai district take a strange model and it has been rampantly increasing c... more Drought occurrences in Rakai district take a strange model and it has been rampantly increasing causing reduced income levels for farmers, reduced farm yields, increased food insecurity and migration, wetland degradation, illness and loss of livestock. The purpose of this study was to investigate past and future characteristics of drought due to climate change in Rakai district. Datasets used include dynamically downscaled daily precipitation and temperature data from Coordinated Regional Climate Downscaling Experiment (CORDEX) at 0.44°×0.44° resolution over the Africa domain. R software (Climpact2 package), was used to generate SPI values, Mann Kendall trend test and Inverse Distance Weighting methods were used to examine temporal and spatial drought characteristics respectively. Results depicted more extreme and severe drought conditions for SPI12 under historical compared to SPI3,Kakuto, Kibanda and Lwanda sub counties were the most drought hot spot areas, positive trends of drou...
The Albany Thicket (AT) biome contains outstanding global biodiversity as well as the potential t... more The Albany Thicket (AT) biome contains outstanding global biodiversity as well as the potential to achieve carbon credits associated with water-efficient Crasslucean acid metabolism (CAM). Understanding the water fluxes in the AT is crucial to determining carbon (C) sequestration rates and water-use efficiency. Despite large variation in water fluxes across the AT, only a few studies have been conducted in this region with their results validated against short periods of observed data. This study aims to evaluate three models of water fluxes over AT against data from an eddy covariance (EC) system active from October 2015 to May 2018. ET was modelled using the BioGeoChemistry Management (BGC-MAN) model, a biophysical model (Penman-Monteith-Leuning (PML)) and a remotely-sensed product (MOD16), and their results compared with that from the EC system. More than three decades of rainfall data from Climate Hazards Group InfraRed Precipitation with Station Data (CHIRPS) was used to assess some rainfall characteristics of the region. The mean annual rainfall is 404 mm and mean monthly rainfall ranges from 16.0-50.7 mm, with minima likely to occur in winter period (between May and July) and monthly maxima in the summer period (between October and March). Among the three hydrological years in this study, total ET for 2016-2017 exceeded rainfall received by about 7% which shows that AT is likely to be supported by groundwater at some point but this requires further investigations. Generally, the three models applied in this study performed reasonably well when compared with the measured ET. The cumulative ET from BGC-MAN was slightly higher than that from EC by 16% and 8% in
The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface m... more The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface mulching with dry grasses/legume, on the infiltration characteristics and intrinsic structural properties of a deep, well-drained soil in southeastern Nigeria are assessed. Treatments are RHD-amended, CD-amended and 'unamended', each plot being either surface-mulched ore bare, with the unamended-bare plots as control. Amendments and mulch were applied at 20 t/ha equivalents. Their effects on the soil's infiltration characteristics 7 months later were not evident; however, there was a tendency for differences: CD-amended ≥ RHD-amended ≥ unamended and surface-mulched ≥ bare-surface. By contrast, saturated hydraulic conductivity (K s) differed thus: CD-mulched ≥ unamended-mulched > the rest. Values were similar for K s (50.89 cm/h) and final infiltration rate (50.74 cm/h) only under CD-amended plots, which also showed the highest transmissivity (43.50 cm/h). Soil penetrometer resistance was lowest in CD-amended plots (113.44 kPa) and highest in unamended plots (166.78 kPa). Topsoil addition of cattle dung and surface mulching could increase infiltration, though marginally, and permeability of coarsetextured tropical soils beyond the season of their application when their effects on soil structure have almost waned.
In order to feed growing populations under scare water resources, a suitable technology that impr... more In order to feed growing populations under scare water resources, a suitable technology that improves crop water productivity (CWP) is crucial. Precision agriculture that utilizes digital techniques such as unmanned aerial systems (UAS) can play a significant role in improving CWP. CWP is an important indicator that quantifies the effect of agricultural water management. To improve CWP, implementation of suitable methods for early detection of crop water stress before irreversible damage on crops occurs, is vital. Conventionally, farmers have relied on in situ measurements of soil moisture and weather variables for detecting crop water status for irrigation scheduling. This method is time consuming and does not account for spatial and temporal variability associated with crop water status. Hence, the aim of this study is to give an overview of the current and potential capabilities of UAS for crop water productivity in precision agriculture. Identified in this study are the factors as well as the technology that can improve CWP. UAS thermal remote sensing is found to be the most suitable technology for monitoring and assessing crop water status using certain indices. Determining a crop water stress index (CWSI) from thermal imagery has the potential to detect instantaneous variations of water status. CWSI obtained from UAS thermal imaging camera can be adapted for real-time irrigation scheduling for maximum crop water productivity. 2014). CWP is an indicator that quantifies the effect of agricultural water management (Sakthivadivel et al., 1999; Sun et al., 2017). The use of CWP helps to meet the rising demand of water by irrigation amidst other sectors and also provide food for the growing population. According to Igbadun et al. (2006), there are many expressions and definitions for quantifying CWP, such as water use (technical) efficiency, which is defined as quantity of agricultural output per unit amount of water used in the production; water use (economic) efficiency, which is
Abstract Interactions between surface water and groundwater systems in fractured rock environment... more Abstract Interactions between surface water and groundwater systems in fractured rock environments, covering large parts of southern Africa, are poorly understood, such that modelling the different water balance components is highly uncertain. Some of these uncertainties are highlighted and attempts are made to resolve them using hypothesis testing with an uncertain ensemble version of the widely used Pitman hydrological model that includes relevant groundwater components. Five study catchments are used to represent many of the major uncertainties in linking surface and groundwater resources, including the relative importance of deep unsaturated zone drainage, the balance between recharge and losses through riparian evapotranspiration and channel transmission losses. The study demonstrates that some uncertainties can be reduced, but this also involves making a number of assumptions about other aspects of a catchment water balance that can be conceptually supported but not completely validated with available data. The remaining uncertainties need to be resolved through improved process quantification and understanding, possibly using environmental tracers. Editor D. Koutsoyiannis; Guest editor G. Mahé
<p>While some progress has been made towards improving the sustainable management o... more <p>While some progress has been made towards improving the sustainable management of water resources, challenges remain. In the water scarce Doring River, in South Africa, these are associated with achieving equitable sharing of the resource among a range of stakeholders which include commercial farmers and emerging farmers.  A participatory water sharing tool has been developed which aims to contribute to  water governance, and includes some key variables such as  the inclusion of uncertainty, environmental Reserve requirements (environmental flows), and the incorporation of socio-economic factors associated with water use. The Institute for Water Research at Rhodes University developed the water sharing tool in response to the <em>Panta Rhei</em> initiative. The tool promotes water sharing at a community level by different water users/user groups, and it encourages deliberation to identify an optimal water sharing (or reallocation) strategy by communicating frequency distributions of assurance shortfall risk. The tool explicitly considers epistemic and alleatory uncertainty; the water users’ value for environmental water requirements; and considers social heterogeneity using socio-economic factors that may influence the way people make water use decisions. However, the tool has never been applied in practice. To complete the tool’s development, a commercial farming setting (i.e. the Doring River in the Koue Bokkeveld region of South Africa) will be used as a case site. The model allocates the available water resource based on the differing impacts on users (impacts of the same deficit will be different for emerging and commercial farmers for example), and produces information which assists the stakeholders to manage the risks of the shortfalls. Ultimately, the stakeholders select the best water sharing option based on a number of possibilities, produced through various combinations of socio-economic factors. In light of growing water scarcity, and the highly uneven distribution of water often found in developing nations, the tool’s approach can be valuable in negotiating increasing water crisis among very different users/user groups.</p>
The connections between surface water and groundwater systems remain poorly understood in many ca... more The connections between surface water and groundwater systems remain poorly understood in many catchments throughout the world and yet they are fundamental to effectively managing water resources. Managing water resources in an integrated manner is not straightforward, particularly if both resources are being utilised, and especially in those regions that suffer problems of data scarcity. This study explores some of the principle issues associated with understanding and practically modelling surface and groundwater interactions. In South Africa, there remains much controversy over the most appropriate type of integrated model to be used and the way forward in terms of the development of the discipline; part of the disagreement stems from the fact that we cannot validate models adequately. This is largely due to traditional forms of model testing having limited power as it is difficult to differentiate between the uncertainties within different model structures, different sets of alternative parameter values and in the input data used to run the model. While model structural uncertainties are important to consider, the uncertainty from input data error together with parameter estimation error are often more significant to the overall residual error, and essential to consider if we want to achieve reliable predictions for water resource decisions. While new philosophies and theories on modelling and results validation have been developed (Beven, 2002; Gupta et al., 2008), in many cases models are not
Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in ... more Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in basin hydrology and overall ecosystem biogeochemistry. Thus, understanding soil erosion patterns in catchments is critical for conservation planning. This study was conducted in a peri-urban Inner Murchison Bay (IMB) catchment on the northern shores of Lake Victoria since most soil erosion studies in Sub-Saharan Africa have been focused on rural landscapes. The study sought to identify sediment sources by mapping erosion hotspots using the revised universal soil loss equation (RUSLE) model in appendage with field walks. RUSLE model was built in ArcGIS 10.5 software with factors including: rainfall erosivity, soil erodibility, slope length and steepness, land cover and support practices. The model was run, producing an erosion risk map and field assessments conducted to ground-truth findings and identify other hotspots. The percentage areas for RUSLE modelled erosion rates were: 66.8% for 0-2 t ha −1 year −1 ; 10.8% for 2-5 t ha −1 year −1 ; 10.1% for 5-10 t ha −1 year −1 ; 9% for 10-50 t ha −1 year −1 and 3.3% for 50-100 t ha −1 year −1. Average erosion risk was 7 t ha −1 year −1 and the total watershed erosion risk was 197,400 t year −1 , with croplands and steep areas (slope factor > 20) as the major hotspots (> 5 t ha −1 year −1). Field walks revealed exposed soils, marrum (gravel) roads and unlined drainage channels as other sediment sources. This study provided the first assessment of erosion risk in this peri-urban catchment, to serve as a basis for identifying mitigation priorities. It is recommended that tailored soil and water conservation measures be integrated into physical planning, focusing on identified non-conventional hotspots to ameliorate sediment pollution in Lake Victoria.
The main objective of this study was to examine the implications of watershed management (WSM) on... more The main objective of this study was to examine the implications of watershed management (WSM) on hydrological parameters in the Aba Gerima watershed in the Upper Blue Nile Basin. The Hydrus 1D model simulations were conducted in control sites and sites under WSM to estimate various components of the hydrologic cycle, using different soil physical & hydrological data under each category of experimental sites. Results were calibrated with measured soil moisture data through inverse solutions. Thus, Hydrus 1D model was found to be effective in predicting results, with R2 values of 0.73 to 0.853 and RMSE values ranging from 0.015 to 0.04. The cumulative evaporation estimated for 365 days for control sites was 37.6% higher than that of sites under WSM. Surface and bottom fluxes in the sites under WSM were 4.6% and 12.5%, respectively, higher than the control sites. This could be attributed to the increased soil water availability resulting from the implemented WSM practices in Aba Gerim...
<p><em>Study aim</em>: To test the performance of 7 glo... more <p><em>Study aim</em>: To test the performance of 7 global hydrological models against local South African datasets from the Earth2Observe platform in terms of the monthly water balance estimation.</p><p><em>Methodology:</em> The remotely-sensed global forcing datasets tested are actual evapotranspiration (ET) and runoff provided by Earth2Observe models. The local datasets were retrieved from the Water Resources of South Africa (WR2012) database, which quantifies the water resources of South Africa, Lesotho and Swaziland per quaternary catchment. The Quaternary Catchments consist of the lowest and most detailed level of operational catchment in the Department of Water and Sanitation (DWS), South Africa. An assessment of outputs between WR2012 and the ensemble outputs available to download from the seven Earth2Observe models (CEH, CNRS, UNIVK, UNIVU, METFR, JRC, and ECMWF) was conducted in South Africa. The mean annual runoff (MAR) time series analysis for the WR2012 and the Earth2Observe models were calculated. The Percentage of Bias (PoB) of each of the seven models with respect to the WR2012 data were computed as: %bias = (MAR<sub>i</sub> - MAR<sub>WR</sub>) x 100/ MAR<sub>WR.</sub></p><p><em>Results:</em> Models JRC, UNIVU, and CNRS showed excessive bias values in large areas while the remaining four models generally exhibited large negative bias values, but with high positive values in the extreme Northeast and the dry areas of the country. The wetter regions of the country (Eastern Cape and KwaZulu Natal) displayed consistent results across all models. Apart from CNRS, all the results have an approximate water balance (precipitation = evapotranspiration + runoff). This is largely due to compensating over or under estimation of both precipitation and evapotranspiration.</p><p><em>Conclusion and Recommendations:</em> The seven models are therefore rendered unreliable for water balance information in South Africa. Additionally, this study shows that ET data from the Earth2Observe platform is reliable to use, but the global runoff datasets should not be used in South Africa. It is recommended that organisations responsible for the generation of these global datasets issue warnings that these outputs have not been validated thus cannot be relied on.</p>
<p><strong></strong></p><p>... more <p><strong></strong></p><p><em>Background/aims</em></p><p>Water scarcity is a significant problem in South Africa. Low average rainfall results in limited water available for human and environmental needs. Consequently, competition for water resources is increasing and has resulted in water-related conflicts among the various water users in many areas of South Africa. Unfortunately, when competition for water use exists, Environmental Water Requirements (EWRs) are often ignored, thus impacting the health of riverine ecosystems and downstream ecosystem services. Such a situation characterises the Koue Bokkeveld farming region. Conflicts are rife between upstream farmers who have initial access to river water and downstream farmers forced to use what remains after upstream users satisfy their needs. The situation entrenches inequality and fuels conflict and, if left unmanaged, may lead to a breakdown in the farming community. The resultant loss in agricultural productivity will affect food security and the livelihood of the thousands of farmworkers who work in the area. This research project responds to this problem by negotiating a shared water management strategy that achieves equity in water access and respects EWR.  The broader aim is to assist Koue Bokkeveld (KBV) stakeholders in co-developing a water resources management strategy that results from a shared understanding.</p><p><em>Methodological framework</em></p><p>To achieve the research aim, a mixed methodological approach driven by Agent-Based Modelling is employed. A companion modelling approach is adopted, thus placing stakeholders at the centre of the model development and application. A series of stakeholder workshops are lined where stakeholders will provide input into and validate the model. Future scenarios (and subsequent impacts on an agreed water management plan) will be evaluated, assisted by hydrological modelling of future flows.</p><p><em>Preliminary results </em></p><p> An initial conceptual ABM model based on literature and an understanding of the study area representing the key actors, resources and dynamics obtained in the catchment has been developed. An initial stakeholder workshop to solicit stakeholder buy-in has been conducted with success. Although stakeholders remain sceptical about their identities and activities being kept in confidence-they are keen to participate in the following workshops.</p><p>Keywords: ABM, South Africa, stakeholder-engagement, water resources, modelling</p>
<p>Changing climate and expanding irrigated agriculture exert significant pressure ... more <p>Changing climate and expanding irrigated agriculture exert significant pressure on the already limited water resources in many regions of the world. This study is located in a South African strategic water source area called the Koue Bokkeveld (KBV). The area is characterised by a strongly seasonal flow regime, where winter flash flood flows dominate and long dry summer periods are experienced. Numerous small reservoirs have been constructed in the catchment to capture the extreme winter flows. The region is a biodiversity hotspot with a number of endemic species and forms part of the strategic water source area in South Africa (10% of South Africa’s land surface produces 80% of the country’s runoff).</p><p>During the long dry summer period, conflicts over water use and allocation among farmers in the study catchment emerge. When this happens, river flows are abstracted without considering ecological reserve (environmental flow) requirements.</p><p>This study quantifies the availability of water resources in the KBV catchment to contribute to creating an equitable and more sustainable water management plan that addresses water-related conflicts among farmers and ensures that ecological reserve requirements are met. SWAT+ has been set up for this study as it allows the representation of spatially distributed reservoirs and river diversion points within a catchment. This study also simulates future flow scenarios in the context of changing climate.</p><p>The outcomes of this project will be used to support decision-making regarding sustainable water management. This includes being used as input into an Agent-Based Model (ABM) that will be utilised to explore various management scenarios. Furthermore, the modelled current and future water availability information will assist catchment managers in making informed decisions about how water management could be adapted to changes in water availability.</p><p>The project is half way through, with SWAT setup complete. A meeting with the farmers in early 2022 will assist with further calibration of the model, in terms of reservoir and irrigation dynamics. The possibility of additional reservoirs will be explored to counter the run of river summer abstraction occurring that is currently negatively impacting the biodiversity.</p>
The Ecological Reserve (environmental flows) as defined under the South African National Water Ac... more The Ecological Reserve (environmental flows) as defined under the South African National Water Act 36 of 1998 was designed to equitably manage water for river sustainability while maximizing economic and social welfare. We investigated the climate change impacts on the Ecological Reserve targets for a seasonal river in an agricultural catchment in the Western Cape region using the Habitat Flow Stressor Response method (which integrates hydrology, hydraulics, water quality, and ecological data) under projected climate scenarios (2041–2070). Current Ecological Reserve model outcomes for 3 sites on the Doring River were compared with the future hydrology using Global Circulation Models associated with four Representative Concentration Pathways (RCP 2.6–8.5). Climate predictions reflected reduced future flows, but the uncertainty band of predicted future flows overlapped with present day flows. Flood flashiness following heavy rains and the increased length of dry periods that are predi...
To increase the resilience of regional water supply systems in South Africa in the face of antici... more To increase the resilience of regional water supply systems in South Africa in the face of anticipated climatic changes and a constant increase in water demand, water supply sources require diversification. Many water‐stressed metropolitan regions in South Africa depend largely on surface water to cover their water demand. While climatic and river discharge data is widely available in these regions, information on groundwater resources – which could support supply source diversification – is scarce. Groundwater recharge is a key parameter that is used to estimate groundwater amounts that can be sustainably exploited at a sub‐watershed level. Therefore, the objective of this study was to develop a reliable hydrological modelling routine that enables the assessment of regional spatio‐temporal variations of groundwater recharge to discern the most promising areas for groundwater development. Accordingly, we present a semi‐distributed hydrological modelling approach that incorporates wa...
Accurately quantifying actual evapotranspiration (ETa) over wetlands is important for the improve... more Accurately quantifying actual evapotranspiration (ETa) over wetlands is important for the improved management of these ecosystems, since 65% of them are threatened by clearing or drainage in South Africa. This study evaluated a range of available estimates of ETa over six palmiet wetlands, which are key ecological structures in terms of water regulation and sediment trapping. The research compared three remote sensing based products (a local product, FruitLook, and two global data products, MOD16 ET and EEFlux) across different rainfall years (2008 to 2019). Their outputs were validated, where possible, with limited ground-based scintillometer data on the Krom palmiet wetland, which indicated that MOD16 and EEFlux were most representative of ground-based measurements. We also compared the small pixel size EEFlux data over three wetlands with ETa over increasing buffers of land cover (100, 500, 1000 m) in order to validate the perception of these wetlands being high water users. Whil...
Drought occurrences in Rakai district take a strange model and it has been rampantly increasing c... more Drought occurrences in Rakai district take a strange model and it has been rampantly increasing causing reduced income levels for farmers, reduced farm yields, increased food insecurity and migration, wetland degradation, illness and loss of livestock. The purpose of this study was to investigate past and future characteristics of drought due to climate change in Rakai district. Datasets used include dynamically downscaled daily precipitation and temperature data from Coordinated Regional Climate Downscaling Experiment (CORDEX) at 0.44°×0.44° resolution over the Africa domain. R software (Climpact2 package), was used to generate SPI values, Mann Kendall trend test and Inverse Distance Weighting methods were used to examine temporal and spatial drought characteristics respectively. Results depicted more extreme and severe drought conditions for SPI12 under historical compared to SPI3,Kakuto, Kibanda and Lwanda sub counties were the most drought hot spot areas, positive trends of drou...
The Albany Thicket (AT) biome contains outstanding global biodiversity as well as the potential t... more The Albany Thicket (AT) biome contains outstanding global biodiversity as well as the potential to achieve carbon credits associated with water-efficient Crasslucean acid metabolism (CAM). Understanding the water fluxes in the AT is crucial to determining carbon (C) sequestration rates and water-use efficiency. Despite large variation in water fluxes across the AT, only a few studies have been conducted in this region with their results validated against short periods of observed data. This study aims to evaluate three models of water fluxes over AT against data from an eddy covariance (EC) system active from October 2015 to May 2018. ET was modelled using the BioGeoChemistry Management (BGC-MAN) model, a biophysical model (Penman-Monteith-Leuning (PML)) and a remotely-sensed product (MOD16), and their results compared with that from the EC system. More than three decades of rainfall data from Climate Hazards Group InfraRed Precipitation with Station Data (CHIRPS) was used to assess some rainfall characteristics of the region. The mean annual rainfall is 404 mm and mean monthly rainfall ranges from 16.0-50.7 mm, with minima likely to occur in winter period (between May and July) and monthly maxima in the summer period (between October and March). Among the three hydrological years in this study, total ET for 2016-2017 exceeded rainfall received by about 7% which shows that AT is likely to be supported by groundwater at some point but this requires further investigations. Generally, the three models applied in this study performed reasonably well when compared with the measured ET. The cumulative ET from BGC-MAN was slightly higher than that from EC by 16% and 8% in
The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface m... more The effects of topsoil addition of rice-husk dust (RHD) and cattle dung (CD), alongside surface mulching with dry grasses/legume, on the infiltration characteristics and intrinsic structural properties of a deep, well-drained soil in southeastern Nigeria are assessed. Treatments are RHD-amended, CD-amended and 'unamended', each plot being either surface-mulched ore bare, with the unamended-bare plots as control. Amendments and mulch were applied at 20 t/ha equivalents. Their effects on the soil's infiltration characteristics 7 months later were not evident; however, there was a tendency for differences: CD-amended ≥ RHD-amended ≥ unamended and surface-mulched ≥ bare-surface. By contrast, saturated hydraulic conductivity (K s) differed thus: CD-mulched ≥ unamended-mulched > the rest. Values were similar for K s (50.89 cm/h) and final infiltration rate (50.74 cm/h) only under CD-amended plots, which also showed the highest transmissivity (43.50 cm/h). Soil penetrometer resistance was lowest in CD-amended plots (113.44 kPa) and highest in unamended plots (166.78 kPa). Topsoil addition of cattle dung and surface mulching could increase infiltration, though marginally, and permeability of coarsetextured tropical soils beyond the season of their application when their effects on soil structure have almost waned.
In order to feed growing populations under scare water resources, a suitable technology that impr... more In order to feed growing populations under scare water resources, a suitable technology that improves crop water productivity (CWP) is crucial. Precision agriculture that utilizes digital techniques such as unmanned aerial systems (UAS) can play a significant role in improving CWP. CWP is an important indicator that quantifies the effect of agricultural water management. To improve CWP, implementation of suitable methods for early detection of crop water stress before irreversible damage on crops occurs, is vital. Conventionally, farmers have relied on in situ measurements of soil moisture and weather variables for detecting crop water status for irrigation scheduling. This method is time consuming and does not account for spatial and temporal variability associated with crop water status. Hence, the aim of this study is to give an overview of the current and potential capabilities of UAS for crop water productivity in precision agriculture. Identified in this study are the factors as well as the technology that can improve CWP. UAS thermal remote sensing is found to be the most suitable technology for monitoring and assessing crop water status using certain indices. Determining a crop water stress index (CWSI) from thermal imagery has the potential to detect instantaneous variations of water status. CWSI obtained from UAS thermal imaging camera can be adapted for real-time irrigation scheduling for maximum crop water productivity. 2014). CWP is an indicator that quantifies the effect of agricultural water management (Sakthivadivel et al., 1999; Sun et al., 2017). The use of CWP helps to meet the rising demand of water by irrigation amidst other sectors and also provide food for the growing population. According to Igbadun et al. (2006), there are many expressions and definitions for quantifying CWP, such as water use (technical) efficiency, which is defined as quantity of agricultural output per unit amount of water used in the production; water use (economic) efficiency, which is
Abstract Interactions between surface water and groundwater systems in fractured rock environment... more Abstract Interactions between surface water and groundwater systems in fractured rock environments, covering large parts of southern Africa, are poorly understood, such that modelling the different water balance components is highly uncertain. Some of these uncertainties are highlighted and attempts are made to resolve them using hypothesis testing with an uncertain ensemble version of the widely used Pitman hydrological model that includes relevant groundwater components. Five study catchments are used to represent many of the major uncertainties in linking surface and groundwater resources, including the relative importance of deep unsaturated zone drainage, the balance between recharge and losses through riparian evapotranspiration and channel transmission losses. The study demonstrates that some uncertainties can be reduced, but this also involves making a number of assumptions about other aspects of a catchment water balance that can be conceptually supported but not completely validated with available data. The remaining uncertainties need to be resolved through improved process quantification and understanding, possibly using environmental tracers. Editor D. Koutsoyiannis; Guest editor G. Mahé
<p>While some progress has been made towards improving the sustainable management o... more <p>While some progress has been made towards improving the sustainable management of water resources, challenges remain. In the water scarce Doring River, in South Africa, these are associated with achieving equitable sharing of the resource among a range of stakeholders which include commercial farmers and emerging farmers.  A participatory water sharing tool has been developed which aims to contribute to  water governance, and includes some key variables such as  the inclusion of uncertainty, environmental Reserve requirements (environmental flows), and the incorporation of socio-economic factors associated with water use. The Institute for Water Research at Rhodes University developed the water sharing tool in response to the <em>Panta Rhei</em> initiative. The tool promotes water sharing at a community level by different water users/user groups, and it encourages deliberation to identify an optimal water sharing (or reallocation) strategy by communicating frequency distributions of assurance shortfall risk. The tool explicitly considers epistemic and alleatory uncertainty; the water users’ value for environmental water requirements; and considers social heterogeneity using socio-economic factors that may influence the way people make water use decisions. However, the tool has never been applied in practice. To complete the tool’s development, a commercial farming setting (i.e. the Doring River in the Koue Bokkeveld region of South Africa) will be used as a case site. The model allocates the available water resource based on the differing impacts on users (impacts of the same deficit will be different for emerging and commercial farmers for example), and produces information which assists the stakeholders to manage the risks of the shortfalls. Ultimately, the stakeholders select the best water sharing option based on a number of possibilities, produced through various combinations of socio-economic factors. In light of growing water scarcity, and the highly uneven distribution of water often found in developing nations, the tool’s approach can be valuable in negotiating increasing water crisis among very different users/user groups.</p>
The connections between surface water and groundwater systems remain poorly understood in many ca... more The connections between surface water and groundwater systems remain poorly understood in many catchments throughout the world and yet they are fundamental to effectively managing water resources. Managing water resources in an integrated manner is not straightforward, particularly if both resources are being utilised, and especially in those regions that suffer problems of data scarcity. This study explores some of the principle issues associated with understanding and practically modelling surface and groundwater interactions. In South Africa, there remains much controversy over the most appropriate type of integrated model to be used and the way forward in terms of the development of the discipline; part of the disagreement stems from the fact that we cannot validate models adequately. This is largely due to traditional forms of model testing having limited power as it is difficult to differentiate between the uncertainties within different model structures, different sets of alternative parameter values and in the input data used to run the model. While model structural uncertainties are important to consider, the uncertainty from input data error together with parameter estimation error are often more significant to the overall residual error, and essential to consider if we want to achieve reliable predictions for water resource decisions. While new philosophies and theories on modelling and results validation have been developed (Beven, 2002; Gupta et al., 2008), in many cases models are not
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