Water Resources: Key Concepts and Definitions

ITEM 7: Water Resources

Aquifers

Aquifers are layers of porous and permeable rock or sediments that transmit groundwater freely. They tend to be limited, at least in their lower part, by impermeable strata, forming an underground water "store." The area where all the pores are completely filled with water is called the saturation zone, and its upper limit is the water table.

Ecological Flow

Ecological flow, also known as minimum or environmental flow, is the portion of a river's flow that is left in the river after extraction for human use (urban, agricultural, industrial, etc.) to ensure the survival of the ecosystems they contain. Water is a basic resource not only for humans but also for these ecological systems. Spain has established that the minimum should be 10% of the normal flow.

Flow

Flow is the volume of water passing through a cross-section of a current per unit of time (m³/s). It varies over time depending on rainfall, the relationship between infiltration and runoff, the existence of vegetation, soil type, slope at the headwaters and margins, and the presence of obstacles.

Water or Hydrologic Cycle

The water or hydrologic cycle is the closed system whereby water continually changes its location and physical state, circulating continuously between land, oceans, and the atmosphere. Driven by solar energy and gravity, it is an endless cycle involving the following processes: storage, evaporation and evapotranspiration, condensation and precipitation, and surface runoff and groundwater flow.

Water Table

The water table is the upper limit of the zone of soil saturation, i.e., of the aquifers. It is used to predict the level and depth of wells, changes in streamflow, groundwater and springs, as well as fluctuations in the level of lakes and even rivers, which receive input from groundwater.

Water Planning

Water planning is the plan for water resource management that aims for the management or distribution of water use. It involves reducing consumption (by encouraging savings, efficient use, reuse, or recycling) and increasing water intake (usually through technical solutions such as dams, water transfers, desalination, etc.).

Salinization of Groundwater

Salinization of groundwater is the increased concentration of salts in the water of aquifers near the coast, rendering the water unusable for domestic and agricultural purposes. It is due to the overexploitation of groundwater, which causes a reduction in the water table, allowing the entry of saltwater into the aquifer.

Overexploitation of Groundwater and Aquifers

Overexploitation of groundwater and aquifers occurs when groundwater is extracted in excess of its ability to recharge (through infiltration of water from precipitation). This results in a lower water table and even exhaustion. Consequences can include the formation of cones of depression in wells, loss of permeability due to compaction, land subsidence, and salinization in coastal areas.

Thermocline

When there is a major temperature difference in a lake or sea between the warmer surface layer and the colder deep layer, the thermocline is the area where the temperature change with depth is at its maximum. This change is often abrupt because the warm and cold water are kept separate by density differences.

Consumptive Uses of Water

Consumptive uses of water are those in which water is used for activities that no longer allow it to be used again. Consumptive uses include urban uses (domestic and service sector), agriculture and livestock, and industrial uses.

Non-Consumptive Uses of Water

Non-consumptive uses are those in which water is used for activities that allow it to be used again. Non-consumptive uses include energy uses (mainly from hydropower and nuclear power plants), recreational uses, and ecological uses (environmental flow).