Hydrogeology (hydro- meaning water, and -geology meaning the study of the Earth) is the area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the Earth's crust (commonly in aquifers). The terms groundwater hydrology, geohydrology, and hydrogeology are often used interchangeably, though hydrogeology is the most commonly used. Hydrogeology is the study of the laws governing the movement of subterranean water, the mechanical, chemical, and thermal interaction of this water with the porous solid, and the transport of energy, chemical constituents, and particulate matter by flow (Domenico and Schwartz, 1998). Groundwater engineering is a branch of engineering which is concerned with groundwater movement and the design of wells, pumps, and drains. The main concerns in groundwater engineering include groundwater contamination, conservation of supplies, and water quality. Wells are constructed for use in developing nations, as well as for use in developed nations in places which are not connected to a city water system. Wells are designed and maintained to uphold the integrity of the aquifer, and to prevent contaminants from reaching the groundwater. Controversy arises in the use of groundwater when its usage impacts surface water systems, or when human activity threatens the integrity of the local aquifer system.
Introduction Hydrogeology is an interdisciplinary subject; it can be difficult to account fully for the chemical, physical, biological, and even legal interactions between soil, water, nature, and society. The study of the interaction between groundwater movement and geology can be quite complex. Groundwater does not always follow the surface topography; groundwater follows pressure gradients (flow from high pressure to low), often through fractures and conduits in circuitous paths. Taking into account the interplay of the different facets of a multi-component system often requires knowledge in several diverse fields at both the experimental and theoretical levels. The following is a more traditional introduction to the methods and nomenclature of saturated subsurface hydrology.
Hydrogeology in relation to other fields
Hydrogeology, as stated above, is a branch of the earth sciences dealing with the flow of water through the subsurface, typically porous or fractured geological material. The very shallow flow of water in the subsurface (the upper 3 m) is pertinent to the fields of soil science, agriculture, and civil engineering, as well as to hydrogeology. The general flow of fluids (water, hydrocarbons, geothermal fluids, etc.) in deeper formations is also a concern of geologists, geophysicists, and petroleum geologists. Groundwater is generally slow-moving; many of the empirically derived laws of groundwater flow can be alternately derived in fluid mechanics from the special case of Stokes flow (viscosity and pressure terms, but no inertial term).
The mathematical relationships used to describe the flow of water through porous media are Darcy's law, the diffusion, and Laplace equations, which have applications in many diverse fields. Steady groundwater flow (Laplace equation) has been simulated using electrical, elastic, and heat conduction analogies. Transient groundwater flow is analogous to the diffusion of heat in a solid, therefore some solutions to hydrological problems have been adapted from heat transfer literature. Traditionally, the movement of groundwater has been studied separately from surface water, climatology, and even the chemical and microbiological aspects of hydrogeology. As the field of hydrogeology has matured, the interactions between groundwater, surface water, water chemistry, soil moisture, and even climate have become clearer. California and Washington both require special certification of hydrogeologists to offer professional services to the public. Twenty-nine states require professional licensing for geologists to offer their services to the public, which often includes work within the domains of developing, managing, and/or remediating groundwater resources. For example: aquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise.
Subjects
One of the main tasks a hydrogeologist typically performs is the prediction of future behavior of an aquifer system, based on analysis of past and present observations. Some hypothetical, but characteristic questions asked would be:
Can the aquifer support another subdivision? Will the river dry up if the farmer doubles his irrigation? Did the chemicals from the dry cleaning facility travel through the aquifer to my well and make me sick? Will the plume of effluent leaving my neighbor's septic system flow to my drinking water well? Most of these questions can be addressed through simulation of the hydrologic system (using numerical models or analytic equations). Accurate simulation of the aquifer system requires knowledge of the aquifer properties and boundary conditions. Therefore, a common task of the hydrogeologist is determining aquifer properties using aquifer tests. In order to further characterize aquifers and aquitards some primary and derived physical properties are introduced below. Aquifers are broadly classified as being either confined or unconfined (water table aquifers); the type of aquifer affects what properties control the flow of water in that medium (e.g., the release of water from storage for confined aquifers is related to the storativity, while it is related to the specific yield for unconfined aquifers).
Aquifers
An aquifer is a water-bearing layer of rock, or of unconsolidated sediments, that will yield water in a usable quantity to a well or spring. Aquifers can be unconfined, where the top of the aquifer is defined by the water table, or confined, where the aquifer exists underneath a confining bed. There are three aspects that control the nature of aquifers: stratigraphy, lithology, and geological formations and deposits. The stratigraphy relates the age and geometry of the many formations that compose the aquifer. The lithology refers to the physical components of an aquifer, such as the mineral composition and grain size. The structural features are the elements that arise due to deformations after deposition, such as fractures and folds. Understanding these aspects is paramount to understanding of how an aquifer is formed and how professionals can utilize it for groundwater engineering.
… excerpt ends here. Continue reading the full article.
