ABSTRACT The Edwards (Balcones Fault Zone) Aquifer is a high-yield aquifer that provides water for municipal, military, irrigation, domestic, and livestock uses in south-central Texas, and it discharges to several springs that support groundwater ecosystems. Natural water cycling in the Edwards (Balcones Fault Zone) Aquifer is driven by recharge, which depends on precipitation and runoff over the catchment area and recharge zone of the aquifer. This chapter analyzes the water fluxes in the Edwards (Balcones Fault Zone) Aquifer and how they vary with climatic variability and might vary with modern-age climatic change. This work also evaluates the safe yield of the Edwards (Balcones Fault Zone) Aquifer under historic climatic conditions, which is ~400 thousand acre · feet, or 493 × 10 6 m 3 , annually. These results have implications for aquifer groundwater extraction and human and environmental water requirements, such that future groundwater extraction must be adaptive to precipitation and recharge fluctuations to preserve groundwater ecosystems.

ABSTRACT The San Antonio segment of the Edwards (Balcones Fault Zone) Aquifer of south-central Texas is one of the most important and prolific karst aquifers in the United States. Extending from Kinney County (west) to Hays County (northeast), it is the primary source of water for the municipal and agricultural communities surrounding the greater San Antonio area. Deposited in Early Cretaceous time, rocks of the Edwards Group vary from 150 to 300 m thick and include eight members with highly variable hydraulic attributes and solubility. Its complex tectonic, weathering, and geologic history has allowed dissolution of the highly soluble members to form a highly transmissive karst aquifer. Regionally, the Balcones fault zone provides pathways that allow captured streams to flow into the aquifer in the contributing and recharge zones. Karstification of the aquifer has occurred by multiple processes, both epigenic and hypogenic, with visual documentation obvious in numerous caves of the area. Currently, overprinting of hypogenic systems by epigenic systems is common. The en echelon down-to-the-south faulting of the Balcones fault zone has resulted in deep burial of the aquifer in the artesian zone, with dissolution at depth driven by numerous processes, including infiltration of chemically aggressive surface water, hydraulic head, mixing corrosion, and biogenic acids. Well production in the artesian zone is commonly limited only by the discharge rate of the pump. The Edwards Aquifer is also noted for its diverse and widespread aquifer-adapted fauna, implying that the aquifer has a well-integrated karst conduit system.

ABSTRACT The Devils River in south-central Texas is recognized as one of the remaining pristine rivers in the state. Adding to its importance, the Devils River is a key tributary to the Rio Grande, providing essential freshwater flows to south Texas and the Rio Grande Valley. An efficient conveyance system for groundwater is shown to have formed in the karst carbonate watershed, located in a semiarid environment with modest distributed recharge, oftentimes less than 1–2 cm/yr. This conveyance system comprises preferential flow pathways that developed coincident with river channels. A strong correlation between wells with high well yield and proximity to higher-order river channels (i.e., within 2.5 km) was used as evidence of the presence of preferential flow pathways. An important observation is that groundwater flow in the Devils River watershed appears to be controlled by the morphology of the area more than the bulk hydraulic properties of the rocks. Flow measurements in the Devils River measured under relatively high- and low-flow conditions support the hypothesis that the river is gaining in downstream reaches. This characteristic leads to perennial river flow being restricted to only the lower reach of the river. Last, essentially all of the recharge to Amistad Reservoir that is derived from the Devils River watershed is contributed as surface flow from the river, and there is minimal underflow or cross-formational flow from the watershed at the point where the watershed abuts Amistad Reservoir.

Abstract Randomness of fracture networks still makes channelized flow a challenge to track in hard-rock aquifers. While not underestimating geological and hydrological criteria that are also handled here through mapping exercises, this study raises an issue of water quality encountered in lifelong boreholes. Chemical classification checked against a recent conceptual model of bedrock aquifers gives birth to a new typology of groundwater in a complex granitic aquifer system located in the SW of Ivory Coast (West Africa). Major ion chemistry, borehole completion data, digital elevation model and satellite images are used to interpret the geochemical water facies as an expression of connexions between the saprolite and the saprock, or transient insulation. From major ions ratios, cumulate mineralization, carbonate equilibrium, stable isotopes, the maturation of ground waters and mixing between bedrock layers are described at seasonal and local scales. The results highlight some vertical feeding of the water table into the main saprock aquifer owing to shortcuts through the saprolite, along with the existence of dead-ends in the hydraulically active fracture network. Also, some influence of fault zones, either drain or barrier, is confirmed on the (Ca, Mg) bicarbonate water facies within the saprock.

Abstract The Eastern Cape Karoo region is water stressed and will become increasingly so with further climate change. Effective and reliable groundwater management is crucial for a development such as the proposed hydraulic fracturing for shale gas. This is especially critical across this region of agriculture and protected ecosystem services. The research, as part of baseline data gathering, aims to characterize the hydrochemistry for both the shallow groundwater (<500 m) and saline groundwater closer to the c. 2–5 km deep shale gas. The classification will be used to determine possible vertical hydraulic connectivity between the shallow and deep aquifers, prior to anticipated hydraulic fracturing. This paper reports on the baseline framework that includes the sampling design and a hydrocensus with field-recorded parameters shown as interpolated maps. This includes electrical conductivity, groundwater level and borehole yield. Together with completed sampling results, these data provide a record against which the environmental impact of hydraulic fracturing and the reinjection of production water can be determined. The research is a critical first step towards the successful governance of groundwater in light of proposed shale gas development in the Karoo. In its absence, effective regulation of the sector will not be effective.

Abstract Pumping tests carried out in three highly tectonized Mediterranean areas, which share similar climate conditions, were used to characterize hard-rock aquifers and examine the issue of the sustainable yield of wells. On the basis of the identified drawdown trends and hydraulic parameters, pumping scenarios were simulated through different methods. The results show that the long-term trend in the drawdown and the initial thickness of the aquifer constrain the sustainable yield of a well. In the worst cases examined, namely those related to an aquifer with a barrier boundary and a delayed response of the aquifer, the sustainable well yield is 1–2 L s −1 . These well discharge values are significant when compared with those found in other regions of the world, and may be related to the dense network of the discontinuities which characterizes the sites.

Groundwater resources in Haiti are considered abundant, with greater than 2 billion cubic meters per year (2 × 10 9 m 3 /yr) of renewable resources and 56 billion cubic meters of reserves. However, groundwater is not available everywhere and many aquifers are often low yielding, discontinuous, or are at risk from saltwater intrusion, overexploitation, reduced recharge, and contamination. Economic development, population growth, and climate change are factors that will increase stress on groundwater resources. Sector leadership, capacity building mechanisms, integrated water policy, and a clear regulatory framework are urgently needed to manage, regulate, and protect Haiti’s groundwater resources to achieve long-term security. Accomplishing this requires technical support and practical references that summarize the groundwater resources and their vulnerabilities, complexities, and opportunities. This chapter includes a summary of knowledge, information, and experience to aid the development and management of Haiti’s groundwater resources, as well as provides an overview of its complex hydrogeology. Five broad hydrogeological environments are differentiated: (1) Unconsolidated alluvium accounts for 26% of Haiti’s land area—it includes a large portion of the country’s groundwater reserves and is the most exploited for irrigation, industry, and potable water; (2) interior sedimentary units account for 32% of Haiti’s land area and include up to 25% of the country’s groundwater reserves—springs from carbonate aquifers are significant sources of water supply throughout the country; (3) reef carbonate accounts for 6% of Haiti’s land area, with locally available coastal karst aquifer systems serving some of the most rural, driest, and impoverished areas of Haiti; (4) semiconsolidated units account for 21% of Haiti’s land area—their low groundwater potential limits rural and urban water use throughout the country; and (5) igneous bedrock accounts for 15% of Haiti’s land area—its discontinuous groundwater reserves are an important source of water in rural and mountainous areas.