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Irrigation and drainage
Evolution of irrigation development
Out of the cultivable area of 28 million ha, almost 26 million ha are classified as suitable for irrigation according to the USDA-Reclamation Bureau Method. Considering the availability of water resources, this area is reduced to 12.5 million ha. Moreover, when economic considerations are included, Turkeys official estimated irrigation potential is 8.5 million ha, of which 93 percent from surface water resources and 7 percent from groundwater.
Irrigation development in Turkey is carried out by the public sector, represented by the DSI (General Directorate of State Hydraulic Works) and the GDRS (General Directorate of Rural Services), or by farmers and groups of farmers. Irrigation development by the public sector is called improved irrigation, while irrigation development by farmers themselves without a project is called public (or also primitive) irrigation. In 1965, less than 0.5 million ha had been developed by the government and about 1.1 million ha by farmers. In January 1994, of the total of about 4.2 million ha under irrigation more than 3.1 million ha had been developed by the DSI and the GDRS. In 2006, of the total of 4.97 million ha almost 3.97 million ha had been developed by the public sector, of which 2.8 million ha by the DSI and 1.1 million ha by the GDRS. Table 6 shows the irrigation area by organization type around 2000.
Of the total area equipped for irrigation, which was 4 860 800 hectares in 2005, about 78 percent used primary surface water resources, 19 percent primary groundwater and 3 percent non-conventional sources of water, see Table 7 and Figure 3 (DSI, 2006). Table 8 shows the source of the water used by public irrigation schemes in the different regions in 2003 (SIS, 2003).
In the irrigation schemes constructed by the DSI and the GDRS, irrigation water is conveyed by different types of canals: trapezoidal canals (classic type) are used in 45 percent of all schemes, while 48 percent use canalettes (half ellipsoidal open canals constructed above the surface of the ground) and 7 percent use pipes. About 71 percent of the area equipped for irrigation uses a gravity distribution system. In 2006, of the total area equipped for irrigation, 92 percent used surface irrigation methods, 6 percent sprinkler irrigation (mostly hand-move) and 2 percent localized irrigation (Figure 4). In the regions of Marmara (Bursa), Thrace (Edirne) and Middle-East (Kayseri), sprinkler irrigation systems accounted for a larger share with 62, 14 and 11 percent respectively. In the Mediterranean region (around Adana) 47 percent used drip irrigation methods. In the remaining regions, only surface irrigation methods were used. In schemes transferred to farmers, on average 92 percent used surface irrigation, 7 percent sprinkler irrigation and 1 percent drip irrigation methods (Wasamed, 2003).
In 2002, 604 231 ha, of which 118 914 ha of DSI-operated schemes and 485 317 ha of irrigation schemes transferred to farmers to manage, could not be irrigated for various reasons, as explained in Table 9. Three years later, in 2005, 678 448 ha could not be irrigated, of which 42 443 ha of DSI-operated schemes and and 636 005 ha of irrigation schemes transferred to farmers to manage. In 2006, the area equipped for irrigation but not irrigated was estimated at 650 000 ha. In 1994, 44 percent of the schemes were larger than 1 000 ha (Figure 5).
Today, in all cities, landscape and public gardens are irrigated, however, data for urban and peri-urban irrigation are not available for the whole of Turkey.
There is no waterharvesting in Turkey. In the past, in the Manisa province of the Aegean region, a water spreading system was used in small vineyards (Akyürek, 1978). However, this has now been replaced by a new irrigation system.
Role of irrigation in agricultural production, the economy and society
Diverse geoclimatic characteristics have led to the development of a wide range of farming systems throughout the country under both rainfed and irrigated conditions. The average yield of irrigated land can be five times that of dry farming land and the average value-added per irrigated hectare is 2.6 times that of one rainfed hectare. While the area equipped for irrigation accounts for less than 20 percent of the cultivated area, it contributes 34 percent to the agricultural GDP derived from crops (Nostrum-DSS, 2006).
In 2006, just over 4.2 million ha, or 86 percent of the equipped area, was actually irrigated (Table 7). In general, the percentage of equipped area actually irrigated varies between 38 and 88 percent, with large regional and annual fluctuations. The long-term average value for DSI irrigation areas is about 65 percent. In 2004, the harvested irrigated crop area was about 4.2 million ha. More than 1.7 million ha or over 40 percent of this area was occupied by cotton, maize and sunflower. Other important irrigated crops are vegetables, fodder, sugar beet, potatoes and wheat, occupying another 1.6 million ha (Table 7 and Figure 6). The average yield for irrigated cereals (wheat and barley) was 4.5 tonnes/ha as against 2.3 tonnes/ha for rainfed cereals. For irrigated pulses (pea, dry beans, cow vetches, and grass pea) the average weighed yield was 4.5 tonnes/ha, for cotton 3.8 tonnes/ha, for sunflower 1.6 tonnes/ha, for maize 5.5 tonnes/ha, for sugar beet 43 tonnes/ha, and for potatoes 26.8 tonnes/ha (TÜIK, 2006). Rainfed crops include field crops (wheat, barley, etc), nut trees (olive, pistachio, walnut, almond, hazelnut and chestnut), and winter vegetables. Of the total rainfed crop production, 42.5 percent comes from rainfed wheat and barley alone (TÜIK, 2006).
The cost of irrigation development varies between US$7 000/ha for small schemes and US$15 000/ha for large schemes (including pump). The costs of operation and maintenance (O&M) vary from US$100/ha for schemes smaller than 1 000 ha (56 percent of the total area), to US$60/ha for schemes larger than 1 000 ha (including dams). After the economic crisis in 2001, prices in Turkey increased five to tenfold and the cost of irrigation development rose sharply, but water prices did not change as much as those of irrigation development for political reasons. Ten years ago, the average cost of irrigation development was estimated at US$1 750/ha for small schemes and US$3 000/ha for large schemes. Water charges are based on cropped area, with different rates for each crop. During 2001-2005, the average water charges for large schemes were estimated as US$83/ha.
In 2004, the Turkish economy earned US$20.9 billion in production value from irrigated areas. This was equivalent to US$19.1 billion in terms of marketable production. In the same year, total O&M costs were estimated at US$416 million. Data for the rehabilitation and modernization of irrigation schemes are not available for the whole of Turkey, however, during planning 10 percent of net return is assigned for the rehabilitation and modernization of irrigation systems. In addition, it was estimated that collectible water fees on the irrigated areas would amount to US$406.7 million. This brings the total net return from irrigation to about US$19 billion.
While agriculture is one of the most important factors in providing employment, the urban population is increasing and the part of the economically active population working in agriculture is declining steadily, from 64 percent in the 1970s to just over 40 percent at present. Of the women working in the agricultural sector, 81 percent are unpaid family workers, 16 percent are self-employed or employers themselves, and 3 percent are regular or casual employees. In rural areas, irrigation is the most important source of employment and an important factor in preventing migration to urban areas. For example, it is estimated that when the irrigated areas reach 6.5 million ha, this will provide work for 2 million unemployed people in rural areas (DSI, 2006). Irrigation also increases the gross domestic agricultural product (GDAP): in 2004 the average GDAP was US$400/ha without irrigation and US$2 000/ha with irrigation. Women represent 64 percent of the agricultural labour force, but more men than women are employed in agricultural water management (for example in irrigation, drainage, and erosion control).
Both the distribution efficiency Ed (the combination of the conveyance efficiency Ec and the field canal efficiency Eb, Ed = Ec × Eb) and the field application efficiency Ea vary depending on regional conditions and the irrigation methods employed. Average field application efficiencies for the country are 84 percent for drip, 80 percent for sprinkler and 55 percent for surface irrigation. Turkeys distribution efficiency shows fluctuations by region and is calculated to be 8797 percent (Wasamed, 2004). The average total project efficiency Ep (Ep = Ed × Ea) depends on the institutions which operate and manage the irrigation systems. In 2001, it was calculated that the total irrigation efficiency was 38 percent in the DSI-operated irrigation schemes and 48 percent in irrigation schemes where the management was transferred to the farmers (DSI, 2006).
Status and evolution of drainage systems
The DSI and the GDRS construct the drainage infrastructure in the irrigation schemes. The main, secondary and tertiary drainage canals are constructed by the DSI, while the GDRS builds the on-farm drainage systems. In total, 20 716 km of drainage canals have been constructed by the DSI, of which 5 133 km main canals, 6 499 km secondary canals and 9 083 km tertiary drainage canals. For the operation, maintenance and repair of drainage canals, 38 278 km of service-road have been built by the DSI (DSI, 2006). The total area drained in irrigation schemes is 340 890 ha. In addition, 113 628 ha of wetlands had been drained by DSI by 2006. During recent decades, the GDRS has carried out many small on-farm water development works, for example on-farm drainage systems and saline and alkaline soils reclamation.
The area protected from flooding amounts to almost 397 302 ha (GDRS, 2006). It was estimated in 1992, that of the total area operated by the DSI, about 41 000 ha was salinized by irrigation. In 2004, the total area salinized by irrigation in Turkey was estimated at 1.5 million ha. An area of 2.8 million ha are affected by waterlogging and drainage problems (Sönmez, 2004).