Well Construction, Cones of Depression, and Groundwater Sharing Approaches
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Environmental Science. Please check back later for the full article.
The importance of groundwater has been made particularly evident in the last decades by the growing use of this part of the water cycle in many human activities. Nowadays, vertical wells are the most common, effective, and controlled systems to obtain water from aquifers. These have replaced other techniques, like drains and spring catchments, and are the only way to obtain water from deep groundwater bodies.
One negative hydrodynamic effect of well abstraction is the generation of an inverted, conically shaped depression around the well that grows as water is pumped, and can negatively affect water quantity and quality in the aquifer and related water masses. If the abstraction rate is growing in a specific well or, more commonly, if there is an uncontrolled increase of the number of active wells in the area, these effects could have a strong impact on the aquifer’s long term groundwater reserves (overexploitation) and, in some specific contexts, the water quality. Major examples of these last processes can be observed in most coastal-touristic areas in arid or semiarid climates around the world, where intensive water exploitation is abundant in aquifers hydraulically connected with the sea. In most of these areas, an excessive abstraction rate causes sea-water to penetrate the inland part of the aquifer (marine intrusion). Another typical example of undesirable groundwater management can be found in many intensive agricultural production areas. An increase in the concentration of nitrogen solute ions in groundwater and soils is associated with excessive fertilizer input. In these farming areas, the spatial distances between wells, their designs and final execution, and the abstraction rates are critical in the generation of more or less penetrative depressions cones that ultimately control the quality of abstracted water.
To prevent these negative effects, several aquifer management methodologies can be used. One common method is to set specific abstraction rules for a discrete number of aquifer management sectors, according to the hydrogeological characteristics of the aquifer (flow and chemical parameters) and its relationship with other water masses. These management plans are usually controlled by national water agencies with support from, or coordination with, private user water communities.
Transboundary or international aquifers need more complex management strategies than national aquifers. These demand a multidisciplinary approach including legal, political, economic, and environmental actions and, of course, a precise (quantitative) hydrogeological understanding of current and future abstraction effects.