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Irrigation and drainage
Evolution of irrigation development
Total irrigation potential has been estimated at 1.9 million ha. Another estimate of potential gives 0.7 million ha for small-scale irrigated sawah rice farming (bunding, levelling and puddling fields for irrigated rice cultivation) in inland valley watersheds and by including the floodplains this potential may reach 1 million ha.
The development of formal irrigation is comparatively recent in Ghana. The first scheme was initiated in the early 1960s and 22 public irrigation schemes existed in the country by 2003 (Table 5). The construction of most of the schemes was supply-driven and often emphasis was on developing exclusively smallholder plots regardless of whether interested smallholder farmers and with irrigation experience were available and willing to cultivate them. In other instances, the sources where supply purchases should be made were fixed by the donor country without the choice of buying from the cheapest source. Informal urban and peri-urban irrigation is practised in and around the big cities of the country, where the urban population provides a ready market for their produce. Informal irrigation is not new in Ghana; for example in the Kumasi area it was found that it has been practised in at least part of the currently irrigated area for more than 30 years.
In 2000, the total water-managed area in Ghana was estimated to be 30 900 ha (Table 6). In fact, this corresponds to the area under full and partial control, as no data are available for wetlands and inland valley bottoms. Nonetheless, there are reports that seasonally flooded flat valley bottoms are coming under increasing use. It is believed that overall about 27 900 ha of the total of 30 900 ha equipped, or 90 percent, were actually irrigated in 2000, while in the 22 public irrigation schemes, only 5 600 ha of the 8 587 ha equipped, or 65 percent, were actually irrigated. This is due to deterioration of the infrastructure because of lack of sufficient funds for maintenance. The bad state of the infrastructure leads to a decline in productivity which is worse in pumped schemes than in gravity-fed schemes. The cost of electricity is one reason for this. Attempts to rehabilitate the schemes are being made. It is estimated that 24 600 ha are equipped for surface irrigation, of which 8 007 ha public schemes, 4 693 ha private schemes and 11 900 ha informal peri-urban irrigation, and 6 300 ha for sprinkler irrigation, of which 580 ha public schemes and 5 720 ha private schemes (Figure 2). Surface water is primarily used to irrigate the developed areas through gravity, pumping or a combination of the two. For most of the irrigation projects in the country, dams have been constructed to store water to be used for irrigating the lands. In a few cases, weirs are built on perennial rivers for irrigation water abstraction. In most of the irrigation schemes in Ghana, supplementary irrigation is practised because during the wet season, it is only at some times that irrigation is required.
The water-managed area in Ghana can be categorized as follows (Figure 3):
- Public schemes: 8 587 ha. Large schemes (> 500 ha) cover 6 010 ha, small schemes (< 100 ha) 592 ha and medium schemes 1 985 ha.
- Private schemes: 10 413 ha.
- Informal peri-urban irrigation: 11 900 ha. This area refers to peri-urban irrigation in the Kumasi area only. It is believed that similar, extensive areas exist around Accra and Takoradi. As some of the informal irrigators use treated water illegally and others use poor quality wastewater, they tend to avoid government agencies and efforts to register them have been met with stiff resistance.
Role of irrigation in agricultural production, the economy and society
The major irrigated crop is rice, with a harvested area of 5 238 ha in 2002. Other frequently produced crops include tomatoes, okra, peppers, aubergine, sugar cane, cucumber, cowpea and maize. In peri-urban schemes, mostly vegetables are grown. Irrigated rice yields vary from 3.5 to 7 tonnes/ha. Nevertheless, the 4.6 tonnes/ha average irrigated rice yield sharply contrasts with the 1.0-1.5 tonnes/ha under uncontrolled water conditions. The mean yield of sawah rice without fertilizer application is estimated between 2 and 2.5 tonnes/ha. Farmers who grow high-value crops such as vegetables with gravity-fed irrigation usually enjoy an increase in income due to irrigation, while farmers who grow rice with pumping schemes tend to be worse off. In informal peri-urban irrigation schemes, gross income for different crop types varies widely but the average is about US$1 200/ha. In general, women are involved in sowing and harvesting whereas men control the water and weeding.
The data situation on irrigation costs is poor and only a few figures are available. The Kpong Scheme in the Greater Accra Region had a development cost of US$2 200/ha (year 2000 cost). In contrast, the Tono Scheme in the Upper East region had a development cost of US$40 000-50 000/ha. These figures may however not be representative because included in the cost are three townships that were built, a club house, a swimming pool, a tarred road network, streetlights and the cost of extending power from the nearest town to the project site. The cost of rehabilitation was found to be between US$400 and 5 000/ha. At the Dawhenya Irrigation Project the farmers are levied about US$110/ha per year as an irrigation service charge. In the specific schemes a lot of pumping is necessary, hence the high cost of the service charge, which includes the cost of power, water and minor maintenance of the system. For the Afife and Ashaiman gravity-fed schemes, the irrigation service charge is US$22/ha per year.
The operators of peri-urban schemes are usually given extension services to improve on their produce. Apart from that, however, they are unsupported and largely overlooked by policy makers. Government Authorities do not interact with them, for example:
- The Water Resources Commission (WRC) is concerned with major users of raw water using machines to lift the water, while peri-urban irrigators usually use manual means to abstract water.
- The Ghana Irrigation Development Authority (GIDA) does not interact with peri-urban irrigation operators because the schemes for which GIDA has overseeing responsibilities are the 22 formal public irrigation schemes only.
Because most of the public irrigation schemes have deteriorated and need some form of rehabilitation, they are operating at low levels of overall efficiency. Water use efficiency at conveyance and field levels is low since no concerted efforts have been made to address the problem of water losses.
Status and evolution of drainage systems
Drainage and irrigation go hand in hand in every irrigation project. However, as a result of persistent poor maintenance, the drainage system sometimes deteriorates with time. Subsurface drains are virtually absent from irrigation schemes in Ghana.