Groundwater management

Groundwater: Water held under the surface of the earth.

Phreatic zone: The area of ground that is permanently saturated.

Aeration zone: The area of land that is only partially saturated or completely unsaturated.

Water table: The boundary between saturated and unsaturated ground. The water table can move up or down.

Groundwater flow or base flow: The movement of water in saturated ground.

Infiltration: When water moves from the surface into the ground below. The infiltration rate is the speed at which water infiltrates and can be measured using an infiltrometer.

A basic infiltrometer

Percolation: The movement of water from unsaturated to saturated ground

Saturated: When all pore space is full and rocks or soil can hold no more water.

Unsaturated: Ground that can still hold more water i.e. there is still room in the pore spaces.

Aquifer: Rocks that can hold water.

Aquiclude: Rock that will not hold water or allow its movement. i.e. they are non-porous and impermeable

Aquitard: A layer of rock that limits the movement of groundwater. It may be non-porous and has low hydraulic conductivity e.g. it is a clay that water finds it hard to pass through.

Abstraction: The removal or extraction (mining) of groundwater

Artesian basin: An artesian basin or aquifer is a confined aquifer containing groundwater under positive pressure. This causes the water level in the well to rise to a point where hydrostatic equilibrium has been reached (balance between pressure on the aquifer and pressure from the aquifer). The diagram below shows an aquifer sandwiched between two aquitards. The aquifer is being recharged from the surface, but it is also been used by humans pumping water out through a well.

Capillary action: The upwards movement of water.

Depletion: When something is reducing, aquifers can become depleted in dry periods or when they are managed unsustainably.

Water Balance

The water balance, is the balance between the amount of precipitation an area receives and the amount of water that it loses through evapotranspiration.

Deficit: When evapotranspiration has exceeded precipitation for a long period. During these arid periods deep groundwater will have to be used or artificial stores e.g. reservoir Recharge: When precipitation exceeds evapotranspiration and groundwater depleted in drier months can be refilled. Usage: When evapotranspiration is greater than precipitation. During this period groundwater will be used and the level of the water table will start to go down. Excess: When precipitation exceeds evaporation and groundwater is recharged. When there is excess water the ground will become saturated and the water table will move up.

GL=Gigalitre (1 billion litres)

CAUSES OF GROUNDWATER USAGE	CAUSES OF GROUNDWATER RECHARGE
Evapotranspiration from shallow stores, capillary action will draw moisture up to near the surface Natural discharge by springs and into lakes, rivers and oceans Artificial abstraction (removal) for domestic, industrial and agricultural use Leakage into nearby aquifers Interbasin transfers	Artificial recharge. Either leakage from irrigation channels and reservoirs or the pumping of water into aquifers. Infiltration and percolation after precipitation or snow melt Seepage from river channels, lakes and oceans Leakage from nearby aquifers Interbasin transfers

Groundwater Pollution

Main sources:

• Agriculture (fertilisers and pesticides)
• Industry (chemicals and metals)
• Landfill sites (decomposing rubbish e.g. batteries and mobile phones)
• Domestic households (non-biodegradable products e.g. shampoo, detergent)
• Sewage (open or broken sewers, lack of water treatment facilities)
• Natural (arsenic, calcium, magnesium and chloride can all occur naturally)

Dubai struggles with environmental problems after growth - NY times article

Ponds caused Bangladesh arsenic - BBC article

Bangladesh arsenic crisis - BBC article

Nutrient pollution harming UK - BBC article

Gaza thirst as sewage crisis mounts - BBC article

Problems of Depletion

• Saltwater intrusion: If aquifers near coastal areas are depleted enough, they may fill back up with saltwater. Once an aquifer has become filled with saltwater, then it is useless for human consumption.
• Drought: Periods of drought can be worsened if groundwater has been depleted. Under normal circumstances groundwater can be relied upon in times of drought. However, if groundwater has been managed unsustainably, then there might be no groundwater to rely. This also increases the risk of crop failure, famine and ultimately death of livestock and humans.
• Ground subsidence: If too much groundwater is removed, then the ground above the aquifer may sink (subside). This has happened in Mexico City, where its growing population has exploited groundwater unsustainably.
• Salinisation: The increased concentration of water, increasing its levels of salinity (saltiness).

India's water use is unsustainable - BBC article

Mexico's sinking city - BBC article

Possible Solutions to Groundwater Depletion and Pollution

• Desalination: Remove the salt from sea water. At the moment, this technology is very expensive and uses a lot of energy. This can not be a solution for landlocked countries e.g. Afghanistan.
• Reduced leakage: A lot of water is lost through leaking pipes and leaking irrigation channels. If repair the leaks, less water will be needed.
• Trade in virtual water: Countries that have a lot of water, can grow and make products that need a lot of water e.g. rice, cotton and beef. Countries that have a shortage of water can by 'thirsty' products from these countries and specialise in industries that use less water.
• Artificial stores: Create more reservoirs that can collect water during the wet season. The only problems is that you will lose some of the collected water through evapotranspiration and change the natural hydrology of the river.
• Recycling of grey water: In homes it is possible to reuse some water if you use biodegradable products e.g. shower water can be used in the garden.
• Drip irrigation: Irrigation can be very wasteful because water misses the vegetation it is intended for and a lot gets evaporated. Drip irrigation is a lot more targeted and only drips water directly onto the stem of the plant.
• Cloud seeding: Experiments have been done by some countries to release chemicals and particles into the atmosphere that stimulates precipitation.
• Water metering: By metering water instead of charging a flat rate, individuals and industries will be a lot more efficient in their use of water so that they get a smaller water bill.
• Effluent controls and enforcement: By setting limits on what industries and households can release into rivers and the ground, you will improve the quality of the water. If you set effluent limits it is very important to monitor the limits and punish individuals and industries who are breaking the law.
• Recycling of contaminated garbage: By recycling products like mobile phones and using rechargeable batteries less dangerous waste is going to be left in landfills.
• Water treatment: Treating all water, by removing solid and chemical waste.