D |
| Dam | A barrier or structure across a stream, river, or waterway for the purpose of confining and controlling the flow of water. |
| Damara | One of the major tribal groups of Namibia. They speak the Damara dialect of Nama. |
| Decade | A range of 10-years time-period. |
| Decentralisation | The process of dispersing decision-making governance closer to the people or citizen. It includes the dispersal of administration or governance in sectors or areas like engineering, management science, political science, political economy, sociology and economics. |
| Deforestation | The conversion of forested area to non-forested area through the removal of trees. |
| Degradation | A process through which the natural environment is compromised in some way, reducing biological diversity and the general health of the environment. |
| Delta | Large deposit of alluvial sediment located at the mouth of a stream where it enters a body of standing water. |
| DEM (Digital Elevation Model) | Representation of elevation as a raster grid of regularly spaced elevation values. These grids can be directly computed (derived) from other elevation information such as contours, topographic maps, and irregularly spaced spot heights or from satellite images. |
| Democracy | A form of government where the population of a society or country controls the government through a process where ministers and leaders are elected through free and fair elections. |
| Denitrification | The reduction of nitrates to nitrites, nitric oxide, nitrous oxide and eventually dinitrogen by microorganisms. |
| Deposit-feeders | Aquatic animals that consume fine particles of organic matter found on and within the bottom sediments. |
| Desertification | The increase of desert-like conditions caused by degradation on arid, semi-arid and subhumid lands. |
| Detritivores | Organisms that consume dead organic matter. |
| Detritus | Dead organic matter; the particulate remains of dead plants and animals. |
| Development | The process of improving the quality of all human lives. Important aspects of development are raising people's living levels, creating conditions conducive to the growth of people's self-esteem and increasing people's freedom of choice. |
| Diarrhoea | A condition resulting in frequent, watery, or loose bowel movements. |
| Diatom | A photosynthetic, single-celled organism enclosed in a shell of silica. |
| Difequane | Or difaqane. A time of immense upheaval relating to the military expansion of the Zulu kingdom in the early 19th century. Sotho-speakers know this period as the difaqane (forced migration); while Zulu-speakers call it the mfecane (crushing). |
| Digital Elevation Model (DEM) | Representation of elevation as a raster grid of regularly spaced elevation values. These grids can be directly computed (derived) from other elevation information such as contours, topographic maps, and irregularly spaced spot heights or from satellite images. |
| Direct use value | The value obtained from raw materials and physical products yielded by ecosystems and their component species. |
| Discharge | Volume of water flowing through a river (or channel) cross-section in unit time. |
| Discharge standards | Standards used to define the maximum acceptable quantity of pollutants that may be discharged into the area from emissions and effluents. |
| Dissolved Oxygen (DO) | A relative measure of the amount of oxygen dissolved in a given medium (often water). |
| Diurnal | Exhibiting a daily cycle, e.g. over one day and one night. |
| DO (Dissolved Oxygen) | A relative measure of the amount of oxygen dissolved in a given medium (often water). |
| Dolerite | A dark, fine-grained igneous rock. |
| Domestic use | Means use of water for drinking, washing, cooking, bathing, sanitation and stock watering purposes. |
| Donga | In South African English, a Donga is a ditch/gully formed by the erosion of soil in the veldt. |
| Downstream | At a point further along the river in the direction of the flow or current. |
| Drainage | The removal of water from an area through natural or artificial processes. |
| Drakensberg Mountains | The highest mountain range in Southern Africa, rising to 3,482 metres in height. |
| Dredging | The removal of sediment and other material from the bottom of waterbodies by a machine equipped with a scoop or suction device. Dredging is often undertaken to maintain sufficient water depth for navigation. |
| Drivers (or stressors) | The physical, chemical and biological variables that influence response indicators and the overall health of the aquatic ecosystem. |
| Drought | Prolonged absence or marked deficiency of precipitation. |
| Drought relief rations | Rations (food and water) distributed to those affected by drought. |
| Dry land cultivation | Agricultural techniques used to cultivate land that receives little rainfall. |
| Dublin Principles | Developed at the International Conference on Water and the Environment, held in Dublin Ireland in January 1992. The four guiding principles for managing freshwater resources contained within the Duplin Principles are (IRC 2006): (1) Freshwater is a finite and vulnerable resource, essential to sustain life, development and the environment; (2) Water development and management should be based on a participatory approach, involving users, planners and policy-makers at all levels; (3) Women play a central part in the provision, management, and safeguarding of water; (4) Water has an economic value in all its competing uses, and should be recognised as an economic good. |
| DWA (Department of Water Affairs, South Africa) | The Department of Water Affairs is the custodian of South Africa's water resources. It is primarily responsible for the formulation and implementation of policy governing this sector. It also has override responsibility for water services provided by local government. |
| DWAF (Department of Water Affairs and Forestry, South Africa) | The name given to the Department of Water Affairs of South Africa until 2009. See DWA. |
| DWEA (Department of Water and Environmental Affairs, South Africa) | Now known as the Department of Water Affairs. See DWA. |
| Dwell time | The period during which a dynamic process remains halted in order that another process may occur. |
| Dysentery | Parasitic infection of the intestines, which left untreated can be fatal. |
