Guidelines to groundwater vulnerability mapping for Sub-Saharan Africa

Published ArticleAn approach to solving the challenges encountered in groundwater vulnerability assessment in Sub-Saharan African countries is discussed in this paper. The aim of this review is to highlight the gaps and difficulties encountered and provide guidelines for groundwater protection measures in sub-Saharan African countries, particularly countries without specific regulations and methodology of carrying out aquifer vulnerability assessments. Highlighted difficulties in groundwater vulnerability mapping in Sub-Saharan Africa include limited data, shortage of skilled professionals, inapplicability of most existing vulnerability methods and non-availability of funds. The numerical, travel time and parametric vulnerability approaches were recommended for use in sub-Saharan Africa based on the unique geomorphological features of the African continent. The goal of outlining the challenges and providing a guideline was to minimise the impact of groundwater pollution and to prioritise groundwater mapping in an aquifer protection assessment

A lumped parameter balance model for modeling intramountain groundwater basins : application to the aquifer system of Shahrekord Plain, Iran

Intramountain basins are the preferred locations for agricultural and socio-economical development in mountain regions. They often consist of considerable subsurface sedimentary fillings which hold an aquifer system suitable for groundwater exploitation. In semi-arid climates with distinct dry and wet seasons, groundwater is the main source of irrigation water in the dry periods. The risk for overdrafting of these basins is realistic when management of exploitation is not based on the water balance of the basin. When the outlet of the basin is narrow, groundwater interaction with surrounding basins is limited and the water balance becomes very sensitive to changes in the balance components, such as increasing pumping rates. This paper presents a lumped parameter water balance model for intramountain basins which incorporates: (1) the water inflow components of diffuse recharge from rainfall, lateral inflow from the surrounding mountains (mountain front recharge) and irrigation return flow on the cultivated land, and (2) the water outflow components as water capture from wells, springs and underground galleries, water loss from evapotranspiration and river and groundwater outflow out of the basin. Although the model has been developed for a specific basin in a semi-arid climate, it can easily be used for other basins in comparable hydrogeological settings. The model has been applied to the Shahrekord basin in central Iran, where intense agricultural activity has required large amounts of groundwater for irrigation in the dry summer months. Consequently piezometric levels have declined nearly continuously during the last decades because of overdrafting. The model has been applied for the period 1990-2004 and some of the water balance components have been estimated by calibrating the model using an optimisation routine. Additionally, some predictive runs have been done with the calibrated model to investigate future development under three different exploitation scenarios

Regional hydrogeology and groundwater budget modeling in the arid Middle Drâa Catchment (South-Morocco)

This study deals with the regional hydrogeology in Middle Drâa Catchment (MDC) in South-Morocco that features 15,000 km2 of semi-arid to hyper-arid conditions and a heterogeneous geological setting. The MDC covers the southern flank of the central Anti-Atlas Mountains reaching the southerly adjacent Saharan Foreland. Pasture and migration are of significant meaning for existence. Important agriculture and settlement concentrate mainly in six date palm oases along the Wadi Drâa relying on both stream flow and uncontrolled groundwater pumping for irrigation. The dominant groundwater exploitation taps the most important alluvial Drâa aquifers that relate to the six Drâa oases. The Drâa aquifers form an interrupted chain of shallow groundwater reservoirs embedded in a hard rock aquitard system veined by a tributary wadi network. The pressure of climate and global change particularly demands the analysis of the groundwater system, the quantification of water availability and scenario projections to derive options of adaptation and mitigation. Accordingly, results of the analysis of groundwater level data, hydrogeochemical and hydrogeological information lead to the characterization of the current state of the groundwater system and the development of the groundwater budget model BIL. The BIL model simulates the lumped annual groundwater availability and response at the Drâa aquifers. Lithological information from mapping surveys and bore log descriptions form the basis of a hydrofacies framework refining the existing concept of the aquifer system in the MDC. The groundwater level response of the Drâa aquifers relates to the re-interpreted distribution of specific yield values. The recent recharge of the Drâa aquifers depends mostly on transmission losses from the regulated inflow from the Upper Drâa Catchment to the Wadi Drâa. Indirect re-charge from floods generating after intense rainfall within the MDC is another source of aquifer replenishment. The analysis of inorganic groundwater composition and stable isotope signature verifies the interpretation of the aquifer system and the main groundwater flow paths. The distribution of the hydrochemical facies and the state of hydrogeochemical evolution hint on significant influence of groundwater pumping for irrigation. Based on the preceding analysis, items of the groundwater balance are pre-processed for each Drâa aquifer individually considering groundwater discharge from one aquifer to another. Ac-cordingly, the BIL model assesses the annual groundwater budget of the Drâa aquifers for the 33 year period 1974-2006. The model results are highly sensitive to changes in indirect recharge from stream flow infiltration, aquifer properties and irrigation-related parameters. The plausibility tests of the model results reveal satisfying accordance with observed piezometric data as available. So, scenarios of climate and global change are analyzed using the BIL model. As climate change has a significant impact on the groundwater availability of the Drâa aquifers and global change even worsens the situation, options of groundwater management are derived from the hydro-geological analysis and the groundwater budget modeling

Groundwater Recharge Potentiality Mapping in Wadi Qena, Eastern Desert Basins of Egypt for Sustainable Agriculture Base Using Geomatics Approaches

In arid and hyper-arid areas, groundwater is a precious and rare resource. The need for water supply has grown over the past few decades as a result of population growth, urbanization, and agricultural endeavors. This research aims to locate groundwater recharge potential zones (GWPZs) using multi-criteria evaluation (MCE) in the Wadi Qena Basin, Eastern Desert of Egypt, which represents one of the most promising valleys on which the government depends for land reclamations and developments. These approaches have been used to integrate and delineate the locations of high groundwater recharge and the potential of the Quaternary aquifer in the Wadi Qena basin. After allocating weight factors to identify features in each case based on infiltration, land use/land cover, slope, geology, topology, soil, drainage density, lineament density, rainfall, flow accumulation, and flow direction, these thematic maps were combined. The results of the GIS modeling led to the division of the area’s groundwater recharge potential into five groups, ranging from very high (in the western part) to very low (in the eastern part of the basin). The zones with the best prospects for groundwater exploration turned out to be the alluvial and flood plains, with their thick strata of sand and gravel. The groundwater recharge potential map was validated using data from the field and earlier investigations. The promising recharging areas show high suitability for soil cultivation. The results overall reveal that RS and GIS methodologies offer insightful instruments for more precise assessment, planning, and monitoring of water resources in arid regions and anywhere with similar setups for groundwater prospecting and management

Hydrological Modelling and Climate Change Impact Assessment on Future Floods in the Norwegian Arctic Catchments

Climate change is expected to alter the hydrological cycle in the Arctic, which would result in the increase in intensity and frequency of hydrological extreme events such as flooding. Noticeably, the changes in flooding due to climate change would severely affect human life, infrastructures, the environment, ecosystem, and socio-economic development in the impacted areas. Hydrological models are state-of-the-art tools for assessing the impact of climate change on hydrological processes. However, performing hydrological simulation/projection in the Arctic is challenging because of the complex hydrological processes and data-sparse features in the region. In consideration of those issues, this PhD research aims: (1) to assess the performances of hydrological models in the Arctic, (2) to investigate the alternative weather inputs for running the hydrological models in the Arctic region with scattered monitoring data, (3) to evaluate the effects of the models’ structure and parameterization and the spatial resolution of weather inputs on the results of hydrological simulations, and (4) to project future hydrological events under climate change impacts using the current hydrological model, and analyse the reliability/uncertainty of the projection. To fulfil the research’s objectives, several methodologies were applied. Firstly, a comprehensive review was conducted to address the current capacities and challenges of twelve well-known hydrological models, including surface hydrological models and subsurface hydrological models/groundwater models/cryo-hydrogeological models. These models have previously been applied or have the potential for application in the Arctic. Next, the physically based, semi-distributed model, SWAT (soil and water assessment tool), was selected as a suitable model, among other potential models, to assess its performance for hydrological simulations and to verify the potential application of reanalysis weather data. Moreover, the SWAT was coupled with multiple ensemble global and regional climate models’ simulations to project the future hydrological impacts under climate change (in 2041-2070). The study areas were mainly focused in the Norwegian Arctic catchments

PADAMOT : project overview report

Background and relevance to radioactive waste management International consensus confirms that placing radioactive wastes and spent nuclear fuel deep underground in a geological repository is the generally preferred option for their long-term management and disposal. This strategy provides a number of advantages compared to leaving it on or near the Earth’s surface. These advantages come about because, for a well chosen site, the geosphere can provide: • a physical barrier that can negate or buffer against the effects of surface dominated natural disruptive processes such as deep weathering, glaciation, river and marine erosion or flooding, asteroid/comet impact and earthquake shaking etc. • long and slow groundwater return pathways from the facility to the biosphere along which retardation, dilution and dispersion processes may operate to reduce radionuclide concentration in the groundwater. • a stable, and benign geochemical environment to maximise the longevity of the engineered barriers such as the waste containers and backfill in the facility. • a natural radiation shield around the wastes. • a mechanically stable environment in which the facility can be constructed and will afterwards be protected. • an environment which reduces the likelihood of the repository being disturbed by inadvertent human intrusion such as land use changes, construction projects, drilling, quarrying and mining etc. • protection against the effects of deliberate human activities such as vandalism, terrorism and war etc. However, safety considerations for storing and disposing of long-lived radioactive wastes must take into account various scenarios that might affect the ability of the geosphere to provide the functionality listed above. Therefore, in order to provide confidence in the ability of a repository to perform within the deep geological setting at a particular site, a demonstration of geosphere “stability” needs to be made. Stability is defined here to be the capacity of a geological and hydrogeological system to minimise the impact of external influences on the repository environment, or at least to account for them in a manner that would allow their impacts to be evaluated and accounted for in any safety assessments. A repository should be sited where the deep geosphere is a stable host in which the engineered containment can continue to perform according to design and in which the surrounding hydrogeological, geomechanical and geochemical environment will continue to operate as a natural barrier to radionuclide movement towards the biosphere. However, over the long periods of time during which long-lived radioactive wastes will pose a hazard, environmental change at the surface has the potential to disrupt the stability of the geosphere and therefore the causes of environmental change and their potential consequences need to be evaluated. As noted above, environmental change can include processes such as deep weathering, glaciation, river and marine erosion. It can also lead to changes in groundwater boundary conditions through alternating recharge/discharge relationships. One of the key drivers for environmental change is climate variability. The question then arises, how can geosphere stability be assessed with respect to changes in climate? Key issues raised in connection with this are: • What evidence is there that 'going underground' eliminates the extreme conditions that storage on the surface would be subjected to in the long term? • How can the additional stability and safety of the deep geosphere be demonstrated with evidence from the natural system? As a corollary to this, the capacity of repository sites deep underground in stable rock masses to mitigate potential impacts of future climate change on groundwater conditions therefore needs to be tested and demonstrated. To date, generic scenarios for groundwater evolution relating to climate change are currently weakly constrained by data and process understanding. Hence, the possibility of site-specific changes of groundwater conditions in the future can only be assessed and demonstrated by studying groundwater evolution in the past. Stability of groundwater conditions in the past is an indication of future stability, though both the climatic and geological contexts must be taken into account in making such an assertion

Yield Erosion Sediment (YES): A PyQGIS Plug-In for the Sediments Production Calculation Based on the Erosion Potential Method

The Erosion Potential Method is a model for qualifying the erosion severity and estimating the total annual sediment yield of a catchment. The method includes a diverse set of equations, which are influenced by different factors such as geology, morphology, climate and soil use. This study describes a PyQGIS YES plug-in, which allows a semiautomatized use of the Erosion Potential Method in Geographic Information System (GIS) environment. In detail, we developed a plug-in using Python programming language that is made up of a series of operations allowing one to estimate sediment production through a wizard procedure. The first stage consists of data preprocessing and involves: (i) loading of the layers (e.g., geological map); (ii) spatial selection of the catchment area; (iii) elaboration of loaded layers (e.g., clipping). During the second stage, the user assigns a relative coefficient to each factor either by selecting a preloaded value from bibliographic sources or by inserting a value inferred from field observations and data. The third stage includes the addition of rainfall and temperature values loaded as: average values, point shapefiles (the plug-in calculates the average monthly values) or tables (the plug-in creates the linear regression depending on altitude). During the final stage, the plug-in executes the equation of EPM Model obtaining the sediment yield value at basin scale. Additionally, the user can use the “squared cell” method choosing the appropriate option in the setting dialogue of the plug-in. This method divides the catchment area in a regularly-spaced grid which allows one to carry out the distribution map of the sediment production during the final stage