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WATER AS A RESOURCE
UGRC 140
Global water budgets
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-offInfiltration
Evapotranspiration
A fraction of the precipitation is returned to the atmosphere by two processes;
Evaporation, driven by solar energy, is the physical conversion of some of the precipitation to water vapour that is returned to the local atmosphere.
Transpiration - the process by which plants release water into the atmosphere
Surface Runoff
The runoff tends to move toward sinks or temporary storage locations such as;
streams/rivers
lakes
wetlands
the ocean
Infiltration
Subsurface water resources
• After every precipitation event, some of 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
Impermeable layer
Infiltration – groundwater storage S
aturated Zone
Vadose Z
one
Subsurface waterSubsurface water is all water stored in all pore spaces of geologic materials below ground surface
Groundwater, in the strictness sense refers to subsurface water in the saturated zone only
It is only this water in the subsurface zones that can be tapped
The top of the saturated zone (or phreatic zone) is defined by the water table where the saturated zone has no overlying confining beds
Subsurface waterIn some cases, the water table coincides with the ground surface
This results in the development of lakes, streams, or wetlands
The water table is not necessarily flat like the top of a table
It may undulate to correspond with the variations in the topography, permeability of overlying material, variations in the depth of the lower confining beds
Subsurface waterGroundwater can be found hundreds of meters or kilometers down the surface
However, due to confining pressures down depth, the pores spaces get closed
In this case, the water holding capacities of the rocks will depend on the development of fractures in the rocks
The process whereby groundwater is replenished through vertical infiltration and percolation is referred to as recharge
Subsurface waterThe porosity (or effective porosity) of the rock or soil determines how much water can be stored
In most situations, there isn’t enough groundwater to be extracted due to limited recharge and/or limited storage
A rock or soil that holds and transmits groundwater that can be tapped in large quantities 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 aquifer
There 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
Aquiclude
Aquiclude
Aquifer
Water level Confined Aquifer
Aquiclude
Aquifer
Water level Unconfined Aquifer
Water table
Aquiclude
Aquifer
Water level Leaky Aquifer
Water table
Aquitard
Aquiclude
Aquifer
Water level Leaky Aquifer
Water table
Aquifer
Aquitard
Subsurface waterA perched aquifer is a saturated zone within the zone of aeration 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 only yields enough water for a household.
Factors that affect groundwater availability
The availability of groundwater is dependent on several factors
Principal amongst these factors is the level of recharge from various sources
Groundwater recharge can be achieved through vertical infiltration and percolation
Recharge can also occur through sub-surface inter-basin flows
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 withdrawal
When groundwater is pumped from wells the groundwater table progressively drops
This drop in the groundwater level is known as groundwater level drawdown
In groundwater resources management studies, our ability to manage draw downs is critical to the sustainable management of the resource
Effects of groundwater withdrawals
As water is progressively pumped through wells tapping an aquifer, a cone of depression develops
A cone of depression is a circular lowering of the water table around the vicinity of the pumping well
When several wells drilled through the same aquifer are pumped progressively, their cones of depression can overlap
Effects of groundwater withdrawal
Unregulated groundwater pumping through wells can adversely affect regional groundwater budgets
Groundwater mining occurs when groundwater withdrawal exceeds the rate at which the aquifers are replenished through recharge
In sustainable groundwater resources management, groundwater withdrawal from wells is regulated in such a way that it does not exceed recharge
Effects of groundwater withdrawals from wells
Groundwater mining over long periods of time can lead to the depletion of the resource
In some serious cases, the aquifers are destroyed by having their permeable entities closed up due to confining pressure and increased withdrawals
High levels of groundwater withdrawals can also lead to ground subsidence as the pore spaces which were previously filled with water close up due to over pumping
OTHER ENVIRONMENTAL PROBLEMS ASSOCIATED WITH GROUNDWATER
water Pollution
To understand water pollution, it is necessary to first understand 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 Earth's surface. It occurs in streams, lakes, and wetlands, as well as bays and oceans
Each source of water has a unique set of contaminants
Because of interconnectivity of groundwater and surface water; the contaminants may be shared between the two sources. Example, pollutions on the surface can leach and be released to the groundwater.
water Pollution
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 natural processes and human activities. Natural processes are as a result of conditions such as geology, climate, the amount and type of vegetation present, etc.
The major causes of water pollution by human activities can be classified as domestic, industrial and agricultural discharges.
Natural: groundwater contains some impurities, even if it is unaffected by human activities. The types and concentrations of natural impurities depend on the nature of the geological material through which the groundwater moves and the quality of the recharge water.
Groundwater moving through sedimentary rocks and soils may pick up a wide range of compounds such as magnesium, calcium, and chlorides. Some aquifers have high natural concentration of dissolved constituents such as arsenic, boron, and selenium. Climate influences water quality because temperature, precipitation, and wind affect the physical, chemical, and biological characteristics of water. In areas where vegetation is abundant, it falls into the 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’t Domestic discharges mainly septic systems and sewerage treatment plants can be a source of many categories of contaminants, including bacteria, viruses, nitrates from human waste, and organic compounds. Septic systems can cause water pollution when they are placed in areas with poor soil conditions, high water tables, or in areas without sufficient area for them to function properly.
• For example, septic systems do not work well when placed in tightly packed, fine-grained soils such as clay, because effluent from the septic tank cannot pass through the soil easily. Instead, it collects at or near the surface of the ground and may run off into nearby waters.
• In addition, improper storage or disposal of household chemicals such as paints, synthetic detergents can lead to groundwater contamination.
• Wastes dumped or buried in the ground can contaminate the soil, streams/rivers and also leach into the groundwater.
Causes of water pollution-con’t
Industrial-Manufacturing and service industries have high demand for water (for cooling, processing and cleaning purposes). Groundwater pollution occurs when used water is returned to the hydrological cycle.
Other sources of contamination include disposing of waste in septic systems or dry wells, storing hazardous materials in uncovered areas or in areas that do not have pads with drains or catchment basins.
• Storage tanks holding petroleum products, acids, solvents and chemicals can develop leaks from corrosion, improper installation, or mechanical failure of the pipes and fittings and thereby polluting water sources.
• Agricultural: Pollution from this category are varied and numerous: runoff during storm of fertilizers into surface water, spillage of fertilizers and pesticides during handling, runoff from the loading and washing of pesticide sprayers or other application equipment, etc.
Effects of water pollution
Virtually all types of water pollution are harmful to the health of humans and animals.
Water pollution may not damage our health immediately but can be harmful after long term exposure.
Different forms of pollutants affect the health of animals in different ways:
Heavy metals from industrial processes can accumulate in nearby lakes and rivers.
• These are toxic to marine life such as fish and shellfish, and subsequently to the humans who eat them.
• Heavy metals can slow development; result in birth defects and some are carcinogenic.
• Industrial waste often contains many toxic compounds that can also damage the health of aquatic animals.
• Some of the toxins in industrial waste may only have a mild effect whereas others can be fatal.
• They can cause immune suppression, reproductive failure or acute poisoning.
Effects of water pollution-con’t Microbial pollutants from sewage often result in infectious diseases that infect aquatic life and terrestrial life through drinking water.
Microbial water pollution is a major problem in the developing world, with diseases such as cholera and typhoid fever being the primary cause of infant mortality.
Organic matter and nutrients causes an increase in aerobic algae and depletes oxygen from the water column. This causes the suffocation of fish and other aquatic organisms.
• Suspended particles in freshwater reduces the quality of drinking water for humans and the aquatic environment for marine life.
• Suspended particles can often reduce the amount of sunlight penetrating the water, disrupting the growth of photosynthetic plants and micro-organisms.
Controlling water pollution
Ideally, pollution should be prevented from occurring because it is more expensive in treating polluted water.
Some of the best opportunities available for preventing water pollution involve 3Rs- reduce, reuse, and recycle.
When we reduce our generation of garbage and other refuse, less solid waste ends up in landfills.
Less solid waste in landfills provides less opportunity for creating leachate,
• reusing treated and disinfected wastewater for irrigation or reusing processed waters for wash down or cleanup
• recycling paper helps prevent water pollution by lowering the demand for raw timber, allowing more trees to remain in the forest for stabilizing the soil, cooling tributary waters, and otherwise benefiting water quality.
Controlling water pollution-con’tThe main goal of treating domestic wastewater is simply to reduce its content of suspended solids, oxygen-demanding materials, dissolved inorganic compounds, and harmful bacteria.
The characteristics of industrial waste waters can differ considerably both within and among industries. Three options are available in controlling industrial wastewater.
Control can take place at the point of generation in the plant; wastewater can be pretreated for discharge to municipal treatment sources; or wastewater can be treated completely at the plant and either reused or discharged directly into receiving waters.
GROUNDWATER RESOURCES OF GHANA
Aquifers underlie almost everywhere in Ghana and can be tapped at relatively shallow depths to provide groundwater
Groundwater quality problems in Ghana
Although groundwater is generally clean in Ghana, there have been cases of contamination
In the Upper East Region (Bongo area), groundwater of extremely high fluoride levels have been noted
High fluoride in groundwater (>1.5 mg/L) can cause dental and skeletal fluorosis
Dental Fluorosis
Skeletal Fluorosis
