When examining the geology of a region for potential useable aquifers, what characteristics or factors would you consider? Also, taking into account certain natural and human factors, which areas would you avoid
EXAMINING THE GEOLOGY OF A REGION FOR POTENTIAL USEABLE AQUIFERS
INTRODUCTIONAn aquifer is a geologic manifestation, with a high concentration of permeable structures, thus providing a source for wells, springs, and water sources. Aquifers are underground layers of porous rock, which allow movement of water between layers of non aqueous rock, such as granite (Ellis, 2008). The movement of water is dependent on two main factors: Movement secondary to pressure changes. Water moves from areas of higher pressure to areas of lower pressure. This pull is important for the formation of aquifers. Secondly, water moves from regions of high altitude, to areas of lower altitude, due to the effect of gravity. These forces constitute the hydraulic head. A positive pressure gradient coupled with the effects of gravity will favour the formation of aquifers (Ouazar, 2006). This movement of water is slow and definite. Infiltration is continuous, between porous rocks, until a zone of saturation is achieved. There is a basement zone of impermeable rock known as the “aquitard” (Ellis, 2008).Water cannot seep through, this impermeable zone, thus resulting in water being held as groundwater. The forces known as “hydraulic head” are responsible for the movement of ground water.
There is a distinct geologic zone, just above the zone of saturation. This is known as the water table (Ouazar, 2006).Tropical regions have a greater depth of water table compared to temperate climates. There are different types of rocks that water can seep through. The two most important types are unconsolidated rock and carbonated rocks.
Unconsolidated rocks are made up of loosely attached particles. This makes it easier for water to move through these spaces. Water moves swiftly through layers of large particles such as gravel, than it does through clay. Carbonated rocks include dolomite and limestone. They are made up of mainly calcium crystals. Calcite, a major constituent of limestone, can be dissolved by groundwater, or precipitated in a chemical reaction known as retrograde solubility. These carbonated rocks are brittle and easily fractured.
There are other rocks classified as impermeable to water. Crystalline and metamorphic rocks are impermeable to water. Examples include granite and slate. However, should they get cracks, fractures, or broken up, water can seep through these gaps, and form a source for aquifers.
- Climate variability
II.Potential sources of artificial recharge
Meteorological events are a predictor to variations in climate change. Recordable daily events critical to mapping out climatic change, are: Highest temperature, lowest temperature, Wind speed, Hailstone coverage, longest dry period, and Maximum rainfall coverage. This will all determine the water table and thus formation of aquifers (Raghunath, 2006).
High temperatures, drive evaporation processes, and encourage desaturation of water tables. This drives a reduction in the zone of saturation. Low temperatures on the other hand, will catalyse a rise in the water tables. Precipitation of water is encouraged, at low temperatures.
Low wind speed will discourage evaporation losses. Thus regions with calm winds are a good predictor to the formation of aquifers (Raghunath, 2006). High wind speeds on the other hand are a bad predictor to the formation of aquifers.
Hailstone coverage will encourage a higher water level, higher saturation levels, and thus sustainance of aquifers. Long dry spells are similar to the effects of sustained high temperatures. There is an association between regions of high rainfall coverage, and the density of wells per square kilometer. This positive link proves that high rainfall coverage is important for the formation of aquifers.
Climate extremes are also an important predictor. Examples of climate extremes include: Storms, Tropical cyclones, Droughts, Floods, Monsoons, Heat waves, and Frost. The dust storms are groups of particles of dust lifted to great heights by powerful winds. This may generate two schools of thought. The basement zone of impermeable rock (carefully examined in the introduction to our paper), requires a zone of impermeable sand particles to form (Raghunath, 2006). The dust storms, may thus encourage a zone of impermeable rock, and thus promote the precipitation of aquifers. On the other hand, a sand storm will discourage settlement of water, thus a decrease in the seepage of water, and drying up of water sources.
A prolonged absence of substantive rainfall, will lead to droughts. A devastating effect of drought is drying up of water sources, and a diminished plant cover. This will be a negative effect to the maintainance of aquifers. Floods are the stark contrast of drought. Geographic regions prone to floods are prone to floodplains. An abundant water supply is an added advantage, to the already set up water bodies.
II.POTENTIAL SOURCES OF ARTIFICIAL RECHARGE.
Potential sources of artificial recharge include irrigation sources, artificial dams, canals, etc. Artificial sources provide a continuous supply of water and renewal. Irrigation sources may aerate the soil surface, and provide an adequate water bed.
These are unplanned natural events that lead to disasters and mass casualties. Natural processes of the earth include earthquakes, tsunamis, volcanic eruptions, landslides, hurricanes etc.An aquifer is filled with flowing water and this amount of water varies (Ellis, 2008). The flow rate of ground water will be altered by any adverse unprecedented natural calamity. On the other hand, water will eventually discharge from an aquifer, and must be replaced. This process will proceed at a slower pace, in the event of a natural calamity.
This refers to the ease with which a natural resource can be located. Geographical disparities such as highlands, mountains, gulleys, valleys, lowlands, etc, may proof a hindrance to the access of natural resources (Ouazar, 2006). A water bed located in a region that is difficult to access will be a hindrance to the maintainance of aquifers.
Legislative processes will determine how our natural resources are catered for. Proper legislation for instance will set out strict penalties to industrial companies that discharge effluent to our water sources. Pollution is a menace that interferes with the natural fauna and flora in our water sources (Ellis, 2008). Pollution also leads to a reduced reserve of fresh water, thus a decrease in the amount of water required for renewal of aquifers.
Policies may also encourage the maintainance of aquifers by Governments. This is a human process that will aid in the setting up of even more water sources.
There is an inverse relationship between the exponential growth in human population and the maintainance of water towers. An increase in the human population will put a strain on the natural resources. There will be an increased need for basic needs such as food and shelter. An increase in the rate of deforestation, as a means of increasing the land cover, will mean decreased rainfall and moisture content in soil.
This entity will prove a negative factor in the maintainance and sustainance of aquifers.
Ellis, Brian. (2008).Impacts Of Urban Growth On Surface Water and Ground Water Quality.Oxfordshire: IAHS Press.
Ouazar, Driss. (2006).Coastal Aquifer Management. (3rd ed).Cape Town: University Press.
Raghunath, M. (2006).Ground Water and Water tables. (2nd ed).New Delhi: New Age International Publishers.