Global water budgets• Globally, the oceans account for the highest percentage of all water on the planet (accounting for about 97.5% of all water)• Land accounts for 2.4%• Atmosphere holds less than 0.001%• Ice sheets account for 1.8% of all water on Earth• Groundwater accounts for 0.63% of Earth’s water budgets• 25.7% of this volume of groundwater is fresh• Saline surface lakes, rivers, and streams account for 0.007%
Global water budgets• Fresh surface water bodies account for 0.009% of all water on the planet• Groundwater is the highest reservoir of useable freshwater on Earth, accounting for about 98% of all freshwater• Groundwater is therefore a very important water supply source all over the world• However, the geologic setting in which groundwater is often found determines how much is locally available as well as its accessibility
The Hydrologic Cycle The hydrologic cycle begins with precipitation in the form of snow or rain, representing the initial input into the hydrologic system.
Precipitation Any form of liquid or solid water particles that fall from the atmosphere and reach the surface of the Earth Caused when a mass of warm, moist air hits a mass of cold air Condensation causes the moisture to form droplets that become rain or crystals that become snow or ice When droplets or crystals become too heavy to be suspended in the atmosphere, they fall to Earth as precipitation
The hydrologic cycle
Aftermath of Precipitation Evapotranspiration Surface run-off Infiltration
EvapotranspirationA fraction of the precipitation is returned to the atmosphereby two processes;Evaporation, driven by solar energy, is the physical conversionof some of the precipitation to water vapour that is returnedto the local atmosphere.Transpiration - the process by which plants release water intothe atmosphere
Surface RunoffThe runoff tends to move toward sinks or temporary storage locations such as; streams/rivers lakes wetlands the ocean
Subsurface water• resources some of After every precipitation event, the water gets the soil soaked up, and if it is sufficiently permeable, some of the water infiltrates vertically down the soil zone• Surface flow occurs only after the soil’s infiltration capacity has been exhausted• The vertical downward movement of water down the soil profile will continue until the water reaches an impermeable boundary
Subsurface water• Water will continue to accumulate over such an impermeable layer until the whole layer of material above the impermeable material gets fully filled with water• The zone in the subsurface, whereby all the pores are filled up with water is referred to as the zone of saturation• Above the zone of saturation, the pores are partially filled with water and partially filled with air• This is the zone of aeration or vadose zone
Infiltration – groundwater storage Vadose Zone Saturated ZoneImpermeable layer
Subsurface waterSubsurface water is all water stored in all porespaces of geologic materials below groundsurfaceGroundwater, in the strictness sense refers tosubsurface water in the saturated zone onlyIt is only this water in the subsurface zonesthat can be tappedThe top of the saturated zone (or phreaticzone) is defined by the water table where thesaturated zone has no overlying confining beds
Subsurface waterIn some cases, the water table coincideswith the ground surfaceThis results in the development of lakes,streams, or wetlandsThe water table is not necessarily flat likethe top of a tableIt may undulate to correspond with thevariations in the topography, permeabilityof overlying material, variations in thedepth of the lower confining beds
Subsurface waterGroundwater can be found hundreds of meters or kilometers downthe surfaceHowever, due to confining pressures down depth, the pores spacesget closedIn this case, the water holding capacities of the rocks will depend onthe development of fractures in the rocksThe process whereby groundwater is replenished through verticalinfiltration and percolation is referred to as recharge
Subsurface waterThe porosity (or effective porosity) ofthe rock or soil determines how muchwater can be storedIn most situations, there isn’t enoughgroundwater to be extracted due tolimited recharge and/or limited storageA rock or soil that holds and transmitsgroundwater that can be tapped in largequantities is referred to as an aquifer
Subsurface water : - Basic terms Aquifer, aquitard, and aquiclude Aquifer • A saturated permeable geological unit that is permeable enough to yield economic quantities of water to wells Examples Unconsolidated sand and gravel (most common examples) Permeable sedimentary rocks (sandstond and limestone) Heavily fractured or weathered volcanic and crystalline rocks
Subsurface water : - Basic terms Aquifer, aquitard, and aquiclude Aquitard • A geological unit that is permeable enough to transmit water in significant quantity, but its permeability is not sufficient to justify production well being placed in it Examples Clays loams shales
Subsurface water : - Basic terms Aquifer, aquitard, and aquiclude Aquiclude • An impermeable geological unit that does not transmit water at all Examples Dense unfractured igneous or metamorphic rocks
Subsurface water : - Basic terms Types of aquiferThere are three main types of aquifer• Confined aquifer• Unconfined aquifer• Leaky or semi – confined aquifer
Subsurface water : - Basic terms Confined aquifer• Bounded above and below by an aquiclude• In confined aquifer, pressure of water is usually higher than atmospheric pressure• A well tapping such an aquifer, the water in it stands above the aquifer• Water that overflows to the ground surface is referred to as artesian well
Subsurface water : - Basic terms Unconfined aquifer• Bounded below by an aquiclude but is not restricted by any confining layer above it• Water in a well penetrating an unconfined aquifer is at atmospheric pressure and does not rise above the water - table
Subsurface water : - Basic terms Leaky aquifer• An aquifer whose upper and lower boundaries are aquitards, or one boundary is an aquitard and the other is an aquiclude• Water is free to move through the aquitards, either upward or downward
Water level Confined AquiferAquicludeAquifer Aquiclude
Water level Unconfined Aquifer Water tableAquiferAquiclude
Water level Leaky AquiferAquitard Water tableAquifer Aquiclude
Water level Leaky Aquifer Water tableAquiferAquitardAquiferAquiclude
Subsurface waterA perched aquifer is a saturated zone within the zone ofaeration that overlies a confining layer.A perched aquifer sits above the main water table.A well may be drilled into a perched aquifer, but it usually onlyyields enough water for a household.
Factors that affect groundwater availabilityThe availability of groundwater is dependent on severalfactorsPrincipal amongst these factors is the level of recharge fromvarious sourcesGroundwater recharge can be achieved through verticalinfiltration and percolationRecharge can also occur through sub-surface inter-basinflows
Factors affecting groundwater availability Our ability to identify and protect groundwater recharge areas is key to managing the resource for development In Ghana, groundwater recharge areas for the major aquifers have not yet been identified and delineated We also need to identify the prolific aquifers and protect them from contamination
Consequences of groundwater withdrawalWhen groundwater is pumped from wells the groundwatertable progressively dropsThis drop in the groundwater level is known asgroundwater level drawdownIn groundwater resources management studies, our abilityto manage draw downs is critical to the sustainablemanagement of the resource
Effects of groundwater withdrawalsAs water is progressively pumped through wells tapping anaquifer, a cone of depression developsA cone of depression is a circular lowering of the water tablearound the vicinity of the pumping wellWhen several wells drilled through the same aquifer arepumped progressively, their cones of depression can overlap
Effects of groundwater withdrawalUnregulated groundwater pumping through wells can adverselyaffect regional groundwater budgetsGroundwater mining occurs when groundwater withdrawalexceeds the rate at which the aquifers are replenished throughrechargeIn sustainable groundwater resources management, groundwaterwithdrawal from wells is regulated in such a way that it does notexceed recharge
Effects of groundwater withdrawals from wellsGroundwater mining over long periods of time can lead to thedepletion of the resourceIn some serious cases, the aquifers are destroyed by having theirpermeable entities closed up due to confining pressure andincreased withdrawalsHigh levels of groundwater withdrawals can also lead to groundsubsidence as the pore spaces which were previously filled withwater close up due to over pumping
OTHER ENVIRONMENTALPROBLEMS ASSOCIATED WITH GROUNDWATER
water PollutionTo understand water pollution, it is necessary to firstunderstand the major sources of water Groundwater Any subsurface water that occurs beneath the water table in soil and other geologic forms Surface water Refers to water on the Earths surface. It occurs in streams, lakes, and wetlands, as well as bays and oceans
water PollutionEach source of water has a unique set of contaminantsBecause of interconnectivity of groundwater and surfacewater; the contaminants may be shared between the twosources. Example, pollutions on the surface can leach and bereleased to the groundwater.
What is water pollution? Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing that drinks or uses or lives (in) it. Water pollution can also make water unsuited for the desired use. Two types of water pollution exist; point source and nonpoint source. Point sources discharge pollutants at specific locations through pipelines or sewers into the surface water. Nonpoint sources are sources that cannot be traced to a single site of discharge. Examples of nonpoint sources are: acid deposition from the air.
Causes of water pollutionWater pollution can be caused by naturalprocesses and human activities. Naturalprocesses are as a result of conditions such asgeology, climate, the amount and type ofvegetation present, etc.The major causes of water pollution by humanactivities can be classified as domestic,industrial and agricultural discharges.Natural: groundwater contains some impurities,even if it is unaffected by human activities. Thetypes and concentrations of natural impuritiesdepend on the nature of the geological materialthrough which the groundwater moves and thequality of the recharge water.
Groundwater moving through sedimentary rocksand soils may pick up a wide range of compoundssuch as magnesium, calcium, and chlorides. Someaquifers have high natural concentration ofdissolved constituents such as arsenic, boron, andselenium.Climate influences water quality becausetemperature, precipitation, and wind affect thephysical, chemical, and biological characteristics ofwater. In areas where vegetation is abundant, it falls intothe water, mixes with it, breaks apart, decomposes,and becomes part of the water. In some cases,excessive decaying vegetation can color the water.
Causes of water pollution-cont’tDomestic discharges mainly septic systems andsewerage treatment plants can be a source ofmany categories of contaminants, includingbacteria, viruses, nitrates from human waste, andorganic compounds. Septic systems can causewater pollution when they are placed in areas withpoor soil conditions, high water tables, or in areaswithout sufficient area for them to function properly.
• For example, septic systems do not work well whenplaced in tightly packed, fine-grained soils such asclay, because effluent from the septic tank cannotpass through the soil easily. Instead, it collects at ornear the surface of the ground and may run off intonearby waters.• In addition, improper storage or disposal ofhousehold chemicals such as paints, syntheticdetergents can lead to groundwater contamination.• Wastes dumped or buried in the ground cancontaminate the soil, streams/rivers and also leachinto the groundwater.
Causes of water pollution-con’tIndustrial-Manufacturing and service industrieshave high demand for water (for cooling,processing and cleaning purposes). Groundwaterpollution occurs when used water is returned tothe hydrological cycle.Other sources of contamination include disposingof waste in septic systems or dry wells, storinghazardous materials in uncovered areas or inareas that do not have pads with drains orcatchment basins.
• Storage tanks holding petroleum products, acids,solvents and chemicals can develop leaks fromcorrosion, improper installation, or mechanical failureof the pipes and fittings and thereby polluting watersources.• Agricultural: Pollution from this category are variedand numerous: runoff during storm of fertilizers intosurface water, spillage of fertilizers and pesticidesduring handling, runoff from the loading and washingof pesticide sprayers or other application equipment,etc.
Effects of water pollutionVirtually all types of water pollution are harmfulto the health of humans and animals.Water pollution may not damage our healthimmediately but can be harmful after long termexposure. Different forms of pollutants affect the health ofanimals in different ways: Heavy metals from industrial processes canaccumulate in nearby lakes and rivers.
• These are toxic to marine life such as fish andshellfish, and subsequently to the humans who eatthem.• Heavy metals can slow development; result in birthdefects and some are carcinogenic.• Industrial waste often contains many toxiccompounds that can also damage the health of aquaticanimals.• Some of the toxins in industrial waste may only havea mild effect whereas others can be fatal.• They can cause immune suppression, reproductivefailure or acute poisoning.
Effects of water pollution-con’t Microbial pollutants from sewage often result ininfectious diseases that infect aquatic life andterrestrial life through drinking water.Microbial water pollution is a major problem inthe developing world, with diseases such ascholera and typhoid fever being the primarycause of infant mortality.Organic matter and nutrients causes an increasein aerobic algae and depletes oxygen from thewater column. This causes the suffocation of fishand other aquatic organisms.
• Suspended particles in freshwater reduces thequality of drinking water for humans and the aquaticenvironment for marine life.• Suspended particles can often reduce the amount ofsunlight penetrating the water, disrupting the growthof photosynthetic plants and micro-organisms.
Controlling water pollutionIdeally, pollution should be prevented fromoccurring because it is more expensive intreating polluted water.Some of the best opportunities available forpreventing water pollution involve 3Rs- reduce,reuse, and recycle.When we reduce our generation of garbage andother refuse, less solid waste ends up inlandfills.Less solid waste in landfills provides lessopportunity for creating leachate,
• reusing treated and disinfected wastewater forirrigation or reusing processed waters for wash downor cleanup• recycling paper helps prevent water pollution bylowering the demand for raw timber, allowing moretrees to remain in the forest for stabilizing the soil,cooling tributary waters, and otherwise benefitingwater quality.
Controlling water pollution-con’tThe main goal of treating domestic wastewater issimply to reduce its content of suspended solids,oxygen-demanding materials, dissolved inorganiccompounds, and harmful bacteria.The characteristics of industrial waste waters can differconsiderably both within and among industries. Threeoptions are available in controlling industrialwastewater. Control can take place at the point of generation in theplant; wastewater can be pretreated for discharge tomunicipal treatment sources; or wastewater can betreated completely at the plant and either reused ordischarged directly into receiving waters.
GROUNDWATER RESOURCES OF GHANAAquifers underlie almost everywherein Ghana and can be tapped atrelatively shallow depths to providegroundwater
Groundwater quality problems in GhanaAlthough groundwater is generally clean in Ghana, therehave been cases of contaminationIn the Upper East Region (Bongo area), groundwater ofextremely high fluoride levels have been notedHigh fluoride in groundwater (>1.5 mg/L) can cause dentaland skeletal fluorosis