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Irrigation and drainage
Evolution of irrigation development
The irrigation potential of land and water resources is estimated to be equal to the cultivable area, or 21.3 million ha. In 2008, the area equipped for irrigation was around19.99 million ha, compared with 15.73 million ha in 1990. The total water managed area is an estimated 21.24 million ha, compared with 16.96 million ha in 1990, and can be divided according to the following classification (Table 4):
- Full control irrigation schemes cover 19.27 million ha, of which 14.87 million ha within the IBIS and 4.40 million ha outside the IBIS. The areas outside the IBIS cover minor perennial irrigation schemes, groundwater schemes including tubwells, wells, karezes and springs. They are located in Khyber Pakhtunkhwa and Balochistan. In Khyber Pakhtunkhwa irrigation is carried out using pump lifts, which are maintained by the Provincial Irrigation Department (PID). In the northern parts of Khyber Pakhtunkhwa contour channels are used to irrigate, offtaking water from the locally available sources, which are often steep sided streams or springs. Most of these schemes are owned and operated directly by the beneficiaries through traditional social organizations. In Balochistan irrigation water is taken from karezes and perennial springs. (Karezes are tunnels or underground channel that tap an aquifer). Irrigation schemes are generally small, ranging between 50 and 400 ha, and operated by a group. . Some small, group-operated schemes, are irrigated from infiltration galleries or small weirs in rivers and individuals may pump water from tubewells and open wells.
- Spate irrigation in 2004 covered a total potential area of 2 million ha (1.4 million ha in 1990). This area refers to potential spate area, but actual area varies based on flood occurrence and frequency and is around 0.72 million ha in an average year. In Pakistan, these areas are known as Rod Kohi in Khyber Pakhtunkhwa and Punjab, or Bandat in Balochistan, and the irrigation method is often called flood irrigation. The streams on the Makran coast and the Karan closed basin are flashy in nature and do not have a perennial supply, thus about 25 percent of their flow, which is less than 5 km3, is used for spate irrigation. This kind of irrigation relies on floods from hill torrents. Wherever possible, the runoff is harnessed for irrigation by weirs or temporary diversion structures. Farmers divert the spate flow onto their fields by constructing breachable earth bunds (called gandas) across the rivers, or by constructing stone/gravel spurs leading towards the centre of the river. Captured water flows from field-to-field and, when the soil profile is saturated, the lower bund is breached to release water into another field. Annual average cropping intensity is 20 percent.
- Flood recession cropping areas cover 1.25 million ha on 2004 (1.23 million ha in 1990). In Pakistan these areas are known as Sailaba, and are often called falling flood irrigation areas. Sailaba cultivation is carried out on extensive tracts of land along the rivers and hill streams subject to annual inundation. Moisture retained in the root zone is utilized after the flood subsides together with subirrigation resulting from the capillary rise of groundwater and any rain.
Apart form these water managed areas, some attempts have been made to develop water harvesting, which is known in Pakistan as Khushkaba, though it is not possible to quantify this area.
In 2008, out of the 19.27 million ha of full control irrigation schemes, 6.91 million ha were commanded by surface water (canals), 4.13 million ha by groundwater (wells, tubewells), whereas 7.96 million ha were commanded by both surface water and groundwater. Only 0.27 million ha were commanded by non-conventional sources of water (Figure 3). Surface irrigation is the only irrigation technique used. In 2008, the entire area equipped for full control irrigation was actually irrigated.
In 2008, small schemes (< 100 ha) covered 21.4 percent of the total area equipped for full control irrigation, medium-size schemes (100-25 000 ha) 2.3 percent and large schemes (> 25 000 ha) 76.3 percent (Figure 4).
The Indus Basin Irrigation System
Although irrigation takes place in other areas of Pakistan, information on the history and development of irrigation generally refers to the IBIS, where more than 95 percent of the irrigation is located.
The 4 000 year old Indus civilization has its roots in irrigated agriculture. Canal irrigation development began in 1859 with the completion of the Upper Bari Doab Canal (UBDC) from Madhopur headworks (now in India) on Ravi river. Until that time, irrigation was undertaken through a network of inundation canals, which were functional only during periods of high river flow. These provided water for Kharif (summer) crops and residual soil moisture for Rabi (winter) crops. The last inundation canals were connected to weir-controlled supplies in 1962 with the completion of the Guddu barrage on Indus river (barrages in the IBIS are constructed to divert river water into canals and the storage capacity is insignificant).
UBDC was followed by Sirhind canal from Rupar headworks on Sutlej in 1872 (also in India) and Sidhnai canal from Sidhnai barrage on Ravi in 1886. The Lower Chenab from Khanki on Chenab in 1892, and Lower Jhelum from Rasul on Jhelum in 1901 followed. Lower and Upper Swat, Kabul river and Paharpur canals in Khyber Pakhtunkhwa were completed during 1885 to 1914.
In the beginning of the 1900s, it became apparent that the water resources of the individual rivers were not in proportion to the potential irrigable lands. Ravi river, serving a large area of Bari Doab, was low in supply while Jhelum had a surplus. An innovative solution was developed in the form of the Triple Canal Project, constructed during 1907-1915. The project linked the Jhelum, Chenab and Ravi rivers, allowing a transfer of surplus Jhelum and Chenab water to the Ravi. The Triple Canal Project was a land-mark in integrated inter-basin water resources management and provided the key concept for the resolution of the Indus waters dispute between India and Pakistan in 1960.
The Sutlej Valley Project, comprising four barrages and two canals, was completed in 1933. This resulted in the development of the unregulated flow resources of the Sutlej river and motivated planning for the Bhakra reservoir (now in India). During the same period, the Sukkur barrage and its system of seven canals, serving 2.95 million ha in the Lower Indus, were completed. These are considered to be the first modern hydraulic structures on the downstream Indus river. Haveli and Rangpur from Trimmu headworks on Chenab in 1939 and Thal canal from Kalabagh headworks on the Indus were completed in 1947. This comprised the system inherited by Pakistan at the time of its creation in 1947.
At independence, the irrigation system, conceived originally as a whole, was divided between India and Pakistan without considering the irrigated boundaries. This resulted in the creation of an international water dispute in 1948, which was finally resolved by the enforcement of the Indus Water Treaty in 1960 under the aegis of the World Bank. The Indus Basin Project (IBP) including Mangla dam, five barrages, one syphon and eight inter-river link canals, was completed during 1960-1971, while Tarbela dam started partial operation in 1975-1976.
After the partition, Kotri, Taunsa and Guddu barrages were completed on the Indus river to provide controlled irrigation to areas previously served by inundation canals. The Taunsa barrage was completed in 1958 to divert water to two large areas on the left and right banks of the river. This made irrigated agriculture possible for about 1.18 million ha of arid landscape in Punjab province. Currently rehabilitation and modernization of the barrage is in progress. Also, three additional inter-river link canals were built prior to the initiation of the IBP.
As a result of these extensive developments Pakistan now possesses the world’s largest contiguous irrigation system. It commands 14.87 million ha (2008) and encompasses the Indus river and its tributaries including three large reservoirs (Tarbela, Mangla, and Chashma), 23 barrages/headworks/siphons, 12 inter-river link canals and 45 canals commands extending for 60 800 km with communal watercourses, farm channels, and field ditches covering another 1.6 million km to serve over 90 000 farmer-operated watercourses. In the Indus system, river water is diverted by barrages and weirs into main canals and subsequently branch canals, distributaries and minors.
The flow to the farm is delivered by over 107 000 watercourses, which are supplied through outlets (moghas) from the distributaries and minors. The mogha is designed to allow a discharge that self-adjusts to variations in the parent canal. Within the watercourse command (an area ranging from 80 to 280 ha), farmers receive water proportional to their land holding. The entire discharge of the watercourse is given to one farm for a specified period on a seven day rotation. The rotation schedule, called warabandi, is established by the Provincial Irrigation and Power Department, unless the farmers can reach a mutual agreement.
Role of irrigation in agricultural production, the economy and society
All cotton, rice, sugarcane, fodder, maize grain, fruits, vegetables, freshwater fisheries, dairy livestock are grown under irrigated conditions, and 90 percent of the wheat area is irrigated. Coarse grains, pulses, groundnut, sorghum and millets are normally rainfed or spate irrigated. Around 10 percent of the wheat area is rainfed,contributing only 5 percent of wheat production. Wheat, pulses and coarse grains are spate irrigated. Recession agriculture is also practiced around the rivers and streams during floods; after receding of floodwater the crops are grown.
In 2008, the total harvested irrigated cropped area was about 21.45 million ha (Table 4 and Figure 5). The major irrigated crops are wheat, rice, sugarcane, cotton and fodder. These crops are almost 78 percent of the total harvested area and consume 82 percent of the total available water resources. The area under these crops is 16.60 million ha, of which 7.33; 2.52; 1.24; 3.05 and 2.46 million ha for wheat, rice, sugarcane, cotton and fodder, respectively (GoP, 2008a).
Full control irrigated agriculture provides 90 percent of wheat and small grains besides nearly 100 percent of sugarcane, rice, cotton, fruits and vegetables, whereas the Barani (rainfed) and Sailaba (spate irrigation) areas contribute only 10 percent of wheat and a portion of small grains and pulses. It also provides milk, meat and fuelwood besides crops (Ahmad, 2004a; Ahmad, 2004b; Ahmad, 2008a; GoP, 2008b). The average yield of irrigated wheat, rice, sugarcane, cotton and fodder is 2.5, 2.2, 51.5, 0.65 and 22.4 tonnes/ha respectively (GoP, 2008a).
In 2008, the average cost of irrigation development in public schemes was an estimated US$1 300/ha, while the cost of drainage development was aroundUS$2 650/ha. The average cost of operation and maintenance (O&M) is US$65/ha per year. The average cost of sprinkler and irrigation for on-farm installation is US$1 500/ha and US$1 750/ha respectively.
Status and evolution of drainage systems
When the IBIS was developed, the drainage needs were initially minimal. Water tables were deep and irrigation water supplies were too low to generate much groundwater recharge and surface water losses. Whatever little drainage was required, could readily be accommodated by the existing natural drainage. The drainage needs, however, have increased as more irrigation water has been diverted and the water table has risen to harmful levels causing waterlogging and salinity. The drainage systems were developed over the last 30-40 years (Bhutta and Smedema, 2005).
Drainage and reclamation programmes to mitigate waterlogging and salinity, especially in areas where the water table is 0-1.5 m deep, have been assigned priority. Under the Salinity Control and Reclamation Projects (SCARPs), a disastrous area of 1.97 million ha (with a water table at 0-1.5 m) was reclaimed through rehabilitation of existing drains and investments for the new drainage schemes. Surface drains were also constructed in areas where surface runoff resulted from rainfall or excess irrigation. To encourage private sector participation in drainage, SCARP tubewells were transferred from the public to private sector. Tile drainage was given due attention. The current situation of the waterlogged area shows that the area at risk (with a water table at less than 1.5 m) comprises 12 percent of the total irrigated area. About 1.06 million ha of this area at risk has been covered under various SCARPs. During the current decade, an area of 1.21 million ha was reclaimed under drainage projects such as LBOD, RBOD-I, II and III, Drainage-IV and the National Drainage Programme with the installation of 1 260 drainage wells, transitioning of 5 000 public tubewells, construction or rehabilitation of 2 200 km of open drains, and laying of tile drainage system in 146 500 ha (MTDF 2005).
In 2008, the total drained area equipped for irrigation, was approximately 15.14 million ha.