Turning water Bodies into wealth Through Engineering. Engineer Albert AyehOgyiri.
President Ghana Institution of Engineers 2011/2012
Since twice as much as the earth’s surface is covered by water as compared to land, which is considered by economists as an important factor of production, it stands to reason that our water bodies should contribute twice as much as the contribution of land to the world’s economy.
In Ghana, our location within the equator zone ensures adequate aggregate rainfall and coupled with a long stretch of coastline, the proper application of engineering would ensure equitable exploitation of our water resources to meet our domestic and industrial requirements thereby stimulate the growth of the economy for enhanced development.
Rainwater Harvesting (RH)
Annual rainfall in Ghana varies from 800mm/year in the South-East to 950mm/year in the North to 2,000mm/year in the South-West.
This contributes to a total annual runoff of 56.4 billion m3. Unfortunately such waters end up in streams and channels causing floods with resultant destruction of life and property. Part of the solution lies in the capture of rainfall, which is clean and safe, for domestic consumption thereby reducing the demand on conventionally treated surface water and subsequently saving costs.
The Ghana National Water Policy (June 2007) proposes the enactment of appropriate legislation and the provision of incentives towards making rainwater harvesting a viable option to supplement household and institutional water requirements. Rainwater Harvesting (RH) systems are simple to install and operate. Running costs are negligible, and they provide water at the point of consumption.
To facilitate rainwater harvesting, the following recommendations may be followed:
- In urban areas where land is scarce, the rainwater storage tanks should be incorporated in the design of buildings and integrated into the plumbing system such that where it is to be used to supplement pipe-borne water supply, it is used for laundry (as soft water, it uses less detergents), gardening and flushing of toilets.
- In rural areas, the storage tanks may be constructed as stand-alone units fitted with taps. It is essential to note that roofs must be constructed with hard surfaced materials.
Other Water harvesting techniques such as Rock catchment, Sand dams and Shallow wells in dry riverbeds may be used to re-charge the groundwater.
RH may also be used in the following applications:
In institutions like schools, community and religious centres to satisfy their water needs. In agriculture, where it can improve yields substantially and at the same time contribute to combating land degradation or flood damage. Simple canal irrigation systems can be designed by constructing weirs upstream of road culverts and diverting the storm run-off to irrigate lower elevations by gravity flow.
Rivers and Streams
Ghana is drained by a large number of streams and rivers. In addition, there are a number of coastal lagoons, the huge man-made Lake Volta, and Lake Bosumtwi created by a meteorite, southeast of Kumasi and which has no outlet to the sea. Lake Volta is one of the world’s largest artificially created lakes. Navigation on the Volta River has changed significantly since 1964.
Construction of the dam at Akosombo, about 80 kilometers upstream from the coast, created the vast Lake Volta and the associated 1,020 megawatt hydroelectric project. Arms of the lake extended into the lower-lying areas, forcing the relocation of 78,000 people to newly created townships on the lake’s higher banks.
Lake Volta is a rich source of fish, and its potential as a source for irrigation is reflected in agricultural mechanization agreement signed in the late 1980s to irrigate the Afram Plains. The lake is navigable from Akosombo through Yeji in the middle of the country and has about 310 landing sites along its stretch; a 24 meter pontoon was commissioned in 1989 to link the Afram Plains to the west of the lake with the lower Volta region to the east. Hydroelectricity generated from Akosombo supplies Ghana, Togo, and Benin.
Hydropower Development
There are five large dams in operation throughout Ghana, the largest are Akosombo (134m high) and Kpong (29 m high). Ghana has 1,072MW of installed hydro capacity, at the Akosombo (912 MW) and Kpong (160 MW) plants. These plants have an average generating capacity of 6100 GWh/year, approximately 58 per cent of the country’s 10,600 GWh/year hydropower potential, evaluated in 1985. The Bui Hydro Project is currently under implementation and expected to come on stream in 2013 with an installed capacity of 400MW. Other planned plants include Juale and Pwalugu. Upgrading projects at the Akosombo and Kpong plants could provide an additional 120 MW of capacity.
Mini-hydro Projects
The prospects of harnessing the hydro-electric potential of small rivers in Ghana have been investigated for over 20 years, leading to the identification of many potential mini hydro sites in the country.
In 1999, the Energy Foundation with support from GTZ/CIM, DANIDA initiated a programme to assess the prospects for the development of mini-hydro potential of the country. Studies that have been used as the basis for this update are the surveys carried out by the then Architectural and Engineering Services Corporation (AESC) in 1985/86 on 16 mini-hydro sites in Ghana and a review conducted by ACRES International in 1991. Studies on other rivers were conducted by ESMAP/ World Bank and data was gathered in the dry season and in the rainy seasons in 2001 and 2002. The potential is summarized below:
The three big rivers Tano, Ankobra and Pra in the Western Region are known as the “Western Rivers”. A study conducted by Coyne etBellier in 1994 analyzes the potential Hydro dam sites at Awisam and TwifoHemang on the Pra river. To harness these mini-hydro potentials for enhanced socio-economic development, the following recommendations were made:
- Consider the implementation of middle or high head sites for hydro-power and where there is a high tourism potential, use the power to develop the tourism potential, e.g. Randall Falls at Kintampo;
- Low head sites are considered to bear the risk of flooding hence may be used for irrigation subject to further detailed analyses of the effect of flooding, e.g. LikpeKukurantumi;
Irrigation
Although Ghana is a well-watered land with about 60% of the population engaged in Agriculture, the total irrigated land area as at 2003 was a mere 310km2 which is about 0.13% of the total land area in Ghana.
Whereas India had the highest irrigated land area of 558,050km2 which represents 16.9% of the total land area, Ghana ranked 10th on the African continent:
Historically, large scale irrigation projects have had marginal success, and the failure has largely been due to lack of maintenance and ineffective operation. However, private irrigation schemes developed and operated by individual farmers have had better successes and therefore it is recommended that more emphasis is placed on designs of simple and small scale schemes for individual farmers.
Waste Water
Grey water is the product that arises as a result of the use of water. Approximately 70% of the water consumption is channelled back into systems largely untreated.
In many places untreated waste water is discharged into the nearest stream because cities in the developing world have few resources to invest in waste water management.
Whereas potable water may be scarce in some areas, grey water is always in constant “supply” and therefore many poor farmers depend on waste water for their livelihoods, it often being the only water available. Occasionally farmers actually prefer such water for irrigation, as the nutrients it contains allows them to save on fertilizer.
In Ghana, farmers in urban and peri-urban areas use polluted water to irrigate vegetable plots and earn annual incomes ranging from $600 to $5,000 per hectare, lifting them above the poverty line.
Since such grey waters are usually collected at low elevations, the challenge to engineers is to design systems that can lift the water to the higher grounds where they can be used for irrigation. The heads involved are usually low and the use of screw pumps would be ideal with the necessary pipework and appurtenances, the handling of the waste water can be reduced to a minimum thereby protecting the farmers from the unhygienic exposure. Land treatment of waste water has also yielded significant results and hence this system of irrigation with grey water may eventually lead to recharge of the groundwater.
Ing. Albert AyehOgyiri, FGhIE, President Ghana Institution of Engineers 2011/2012
Conclusion
Water in its various forms, sustains life on this planet and provides a major resource for our socio-economic, cultural and environmental well-being.
However, the economic wealth in the rivers, lakes, rainwater, groundwater, lakes, lagoons, glaciers, ocean, wetlands and waste water can only be released through engineering to achieve the development and quality of life desired.
The engineering practitioner is key in harnessing this wealth for national development: Generation of energy to run our industries and for domestic consumption; Water Supply for industrial, domestic consumption and preservation of health; Enhancing agricultural production through irrigation schemes; Maintaining the ecosystem through flood control; Enhancing fisheries production; Developing infrastructure to our water resources to enhance tourism and recreation.
