Water is a very important resource. Its importance cannot be emphasized as every living creature requires it for metabolic processes, besides, other processes that occur naturally on earth require water. For example, most of the geological processes on earth are accelerated by this precious resource, these include erosion and other earth forming processes.
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97% of all water found on earth is present in oceans or seas, this makes it salty and can only be used for industrial or recreational purposes. Desalination is a very expensive way to produce water for domestic use. The remaining 3% is fresh, of which three quarters exists in frozen state in the Polar Regions. The rest is found below the ground while a small proportion is found above the ground or in the air.
Groundwater accounts for approximately 20% of all fresh water on earth and exists below the ground level in soil spaces and fissures in underground rocks. These rocks are known as aquifers. Groundwater can flow to the earth’s surface naturally or artificially. It flows to the surface naturally through springs and can form oases or wetlands that eventually flow through the influence of gravity to form rivers.
It can also be pumped out through wells and boreholes and used for household, commercial, and agricultural purposes. Since groundwater contains little or no polluting materials, it is a very important source and can sustain large populations for many years if it is used efficiently (Thomas and Tellam, pp. 158). Managing such resources requires special tools and this is where GIS becomes useful.
GIS, short for geospatial information system, is a method used to capture, store, evaluate, and present information relating to different locations on earth. It combines cartography, statistical analysis, and database management and is applied in archaeology, geography, remote sensing, public land management, natural resource management, and urban planning, among others.
GIS is applied in numerous fields of geography and has most recently been used to map and quantify groundwater. This process aids in the harvesting of these water resources, management, and reducing contamination of the same.
For example, during urban planning, it is imperative that underground water resources are identified so that structures such as industrial plants, landfills, and sewage recycling or disposal areas do not contaminate them. Besides, in the event of groundwater pollution and the need for a subsequent clean up, an existing map of the groundwater system would be very useful.
In this paper, we will look at how GIS systems can be applied to groundwater resource management and protection.
Groundwater Management through GIS Systems
Predicting Groundwater Quality
Groundwater resources around the world are generally underused due to an increased likelihood of contamination. The risk of contamination increases when the groundwater is located in a town center or city. However, a GIS system can be used to predict water quality before construction of a borehole commences in an urban area.
The system uses a probabilistic risk based management tool to establish the contamination levels of groundwater based on the structures that exist in the vicinity of the potential borehole area (Tait et al, pp. 1111).
This ensures that boreholes are only constructed in areas within the city where the water quality meets the conditions for its use, whether human, industrial, or for irrigation. Since the construction of a borehole is a tedious and expensive process, it is imperative that the water extracted meets the requirements for its use.
The level of contamination or purity can be achieved through a GIS-based system. The GIS system uses information on the city’s sewerage system, industrial plants, landfills, charge recharge, and other sources of pollution and calculates the water contamination levels through a simulation process (Tait et al, pp. 1112, Thomas and Tellam, pp. 158). It uses the pre-installed program to perform this process.
This is important as it helps in determining the best sites for constructing underground wells and boreholes. Despite its relative accuracy, the model cannot exactly simulate the intricate interactions between a city and its underground water resources due to natural uncertainties.
Knowledge of Discharge and Recharge
Groundwater goes through the water cycle and hence effective management of this resource requires that we have a working knowledge of its discharge and recharge. Discharge and recharge is the exchange of water between the saturated zone, unsaturated zone, land surface and the atmosphere (Lin et al, pp. 460).
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Knowledge of this cycle is important as it aids authorities in managing the supply of water within ciiities and municipalities. Early discharge-recharge studies were tedious and required a lot of time, however, application of GIS technology can considerably reduce the time spent on these studies with increased accuracy.
This is made possible by the GIS system’s ability to process geospatial data spread across numerous datasets, this is an improvement of traditional systems as the GIS systems is able to handle missing data and make estimations depending on past analyses.
The ability of the system to pool studies from different geographical locations permits faster analysis of recharge and discharge data, hence gives authorities a hint as to groundwater levels at different locations within the city, it can then make plans on how to transport water resources to areas with deficits.
A GIS system for studying discharge recharge can identify and distinguish natural variables to make predictions for future underground water levels, hence authorities are able to make informed decisions regarding the distribution of water resources.
Likelihood of Nitrate Contamination
Leaching of chemicals is common in agricultural areas, unfortunately, they reach the underground water and thus contaminate it. Among the toxic chemicals that are mostly found in underground water is Nitrates (NO3).
High levels of this chemical in water causes blue baby syndrome, hence there is need to investigate the likelihood of nitrate pollution of an underground water resource, again, a GIS system can come handy in this process (Lake et al, pp. 316).
The system consists of a model based on the nitrate levels of the water leaving the root zone of a piece of land, presence of low-permeability superficial material, and the type of rock that makes the aquifer (Lake et al, pp. 316).
The system creates models of underground water vulnerability using GIS to link information regarding soil leaching, soil characteristics, permeability of the soil, and the type of rocks that make up the aquifer. These variables are then used to determine the likelihood that underground waters have been contaminated with nitrates.
Quantity and Quality of Recharge
Effective urban planning requires that authorities are well informed on the quantity and quality of the recharge, usually, this is rarely done. A GIS program can be used to assist urban planners in determining the volume and constituents of the recharge. The program also determines the processes that are most active in contaminating underground water in cities.
The program can also serve as a tool for identifying the connection between land use and contamination of groundwater. Preliminary results indicate that recharge is higher in cities (or paved areas) than in rural areas (or non-paved areas), hence recharge rate is higher in cities. However, this also implies that contamination levels are higher in cities than in rural areas (Thomas and Tellam, pp. 177).
Quantification of Rainfall and Flooding Effects
A final application of GIS in managing underground water resources is in the documentation of rainfall and flooding effects on underground water levels in areas where irrigation is practiced (Khan et al, pp. 359). It is observed that areas in which irrigation is carried out in large scale regularly have a higher water table wich results in salinization of underground water.
Heavy rainfall further increases the salinity. Therefore, it is vital that we comprehend the regional underground water dynamics in order to implement sound land and underground water management. A GIS system is important in assessing these dynamics.
This system maps the net groundwater recharge due to flooding and irrigation for an area that experiences heavy irrigation. After analysis, the mapping may show a spatial arrangement of the effect of flooding on the water table and salinity of underground water (Khan et al, pp. 366). This information can enable city authorities to devise better ways protecting groundwater from pollution.
Khan, Shahbaz, Ahmad, Aftab and Wang, Butian. Quantifying Rainfall and Flooding Impacts on Groundwater Levels in Irrigation Areas: GIS Approach. Journal of Irrigation and Drainage Engineering, Vol. 133, No. 4, 2007. 359-367.
Lake, Iain R. Evaluating factors influencing groundwater vulnerability to nitrate pollution: developing the potential of GIS. Journal of Environmental Management 68 (2003). 315–328.
Lin, Yu-Feng, Wang, Jihua, and Valocchi, Albert J. A New GIS Approach for Estimating Shallow Groundwater Recharge and Discharge. Transactions in GIS, Vol.12(4), 2008. 459–474.
Tait, N. G., et al. Borehole Optimisation System (BOS)—A GIS based risk analysis tool for optimising the use of urban groundwater. Environmental Modelling & Software, 19 (2004). 1111–1124.
Thomas, Abraham and Tellam, John. Modelling of recharge and pollutant fluxes to urban groundwaters. Science of the Total Environment , 360 (2006). 158– 179