A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Darcy's Law
A equation that states that flow through porous media is directly proportional to hydraulic head and inversely proportional to the length of flow. Henri Darcy was a French engineer who worked at the Dijon water works in the mid 19th century. His "law" is the basis for much of the science of ground water hydrology and one of the most important basic equations used in hydrogeologic calculations.

Desalinization
The removal of salts from saline water to provide freshwater. Techniques include the use of membranes and distillation. The high costs of energy make desalinized water expensive.

Developed Water
Water in a specific area that has been added to the hydrologic water system through engineering strategies.

Discharge
The volume of water that passes a given location within a given period of time. Usually expressed in cubic feet per second for surface flow (or M3/sec) as gallons per minute (L/sec) for discharge from wells.

Disinfection by-products
Chemicals that result as by products from water treatment. The most common of which are trihalomethanes that can result from chlorine combining with naturally occurring carbon.

Diversion
Removing water from rivers or lakes by pumping or by structures such as a ditch, canal or siphon.

Domestic Water Use
Water used for household purposes, such as drinking, food preparation, bathing, washing clothes, dishes, flushing toilets, and watering lawns and gardens. About 85% of domestic water in the U.S. is delivered to homes by a public supply facility, such as a county water department. About 15% of the USA's population supply their own water, mainly from wells.

Drainage Basin
The topographic land area that contributes flow to a river/ lake/wetland as defined by a particular point of reference. Sometime referred to as a catchment area. Large drainage basins, like the area that drains into the Mississippi River contain thousands of smaller drainage basins. Also called a "watershed." The area contributing water to a particular reference point in a aquifer system is known as a phreatic catchment. Because of geologic structure, topographic and phreatic catchment areas may not exactly coincide, especially when small areas are considered.

Drawdown
The change of ground water level caused by pumping measured as the difference between the static water level and the water level at a particular well location after a specific period of pumping.

Drip Irrigation
A common irrigation method where pipes or tubes filled with water slowly drip onto crops. Drip irrigation is a low-pressure method of irrigation and less water is lost to evaporation than high-pressure spray irrigation.

Dual purpose wells
Wells designed with the capability of pumping water underground during artificial recharge and to the surface from the aquifer during recovery. See also ASR (Aquifer storage and recovery)