Rechna Doab Benchmark Basin, Pakistan

Area
The gross area of the Doab is 2.97 million hectares, including 2.3 million hectares of cultivable land. It has a maximum length of 403 km and maximum width of 113 km.

Location

Climate
The area is subtropical, continental lowland, designated as semi-arid. The climate is characterized by large seasonal fluctuations of temperature and rainfall. Summers are long and hot, lasting from April through September with maximum temperatures ranging from 21oC to 49oC. The winter season lasts from December through February, with maximum temperature ranging from 21oC to 27oC during the day and sometimes falling below zero at night.

Rainfall;
Mean annual precipitation is about 650 mm in the Upper Rechna, and 375 mm in the Central and Lower Rechna Doab. Nearly 75 percent of the annual rainfall occurs during the monsoon season lasting from mid-June to mid-September.

Aquifer
The Rechna Doab is underlain by an unconfined aquifer with a depth ranging from 300 to 500m. The underlying deposits in Rechna Doab have little vertical or horizontal continuity. The bulk of alluvium is built of silt and fine sand or a mixture with an absence of a thick layer of clay. The horizontal permeability is greater than the vertical permeability. Based on pumping tests, the average specific yield of the aquifer was estimated as 14 percent. Groundwater quality in the upper Rechna Doab and along the two rivers is good but deteriorates down the Doab and with increase in the distance from the rivers.

Soils and topography
Alluvial deposits transported by the Indus and its tributaries form the Rechna Doab. The soils are predominantly medium textured to moderately coarse with favorable permeability characteristics and are generally low in organic matter and are adaptable to a wide variety of crops. Soil pH is generally basic, in the range of 8 to 8.5.

The topography of the Rechna Doab is relatively flat with land surface gradient ranging from about 0.25 m per km in the north and northeast to less than 0.2 m per km towards the south and southwest down the Doab.

Irrigation System
Due to scanty rainfall as well as its unfavorable seasonal distribution, agriculture is not possible without irrigation in Rechna Doab. The modern irrigation system was introduced in Rechna Doab through the construction of the Lower Chenab Canal (LCC) in 1892. Presently, the Rechna irrigation network consists of five canal commands and as many inter-river link canals (Tables 1 & 2). The normal flow period for the perennial canals is about 340 days per year. The outlets (moghas) from the distributaries are designed to deliver a fixed quantity of water when the canal is flowing at full capacity and design flows are based on the command area. Each farmer is allotted a fixed quantity of water proportional to his land holding on a weekly or 10-day rotation period locally called "Warabandi".

*Some link canals in the IndusBasin Irrigation System, in addition to transferring of water from one river system to another, also supply irrigation water to either one or a number of irrigation channels off-taking directly from the link canal. Such irrigation channels (collectively) are designated as Internals.

Table 2

This system was designed to spread a limited amount of canal water over the entire area to support approximately 65 percent cropping intensity during a year. The major design objective of irrigation development at that time was to protect against crop failure and prevent famine. However, the cropping intensities have drastically increased (up to 150%) due to massive groundwater development and after the completion of the Indus Basin Works (including three major reservoirs and some link canals) that were initiated after the signing of the Indus Basin Treaty between India and Pakistan under United Nations/World Bank auspices in 1960.

Agriculture
The Rechna Doab falls in the rice-wheat and sugarcane-wheat agro-ecological zones of the Punjab province. The soils are adaptable to a wide variety of crops and temperatures allow year-round cropping. Rice, cotton and forage dominate the summer season (Kharif: May to October), while wheat is the major winter crop (Rabi: November to April). Sugarcane, which is an annual crop, is also cultivated.

Key issues related to agricultural water management
Like the rest of Pakistan, the Rechna Doab is also faced with serious issues related to poor water and land productivity for different reasons. Inequity in surface water distribution at all levels of the canal system, and lack of reliable and adequate supplies to meet the food needs of an increasing population are some important issues that need immediate and focused attention. A serious threat to the sustainability of irrigated agriculture is the mining of groundwater resources. In fresh groundwater areas farmers are using groundwater, mostly in conjunction with canal water, for expansion of their cropped area and high cropping intensity

The mushrooming growth of tubewells in recent years leading to depletion of groundwater, the use of poor quality groundwater for agriculture and secondary salinization are other factors threatening the sustainability of irrigated agriculture in the area. Similarly, the lack of institutional mechanisms for regulating groundwater resources and reallocating the surface water for more beneficial and productive purposes is another constraint in productive irrigated agriculture.

Waterlogging used to be a threat to agriculture in Rechna Doab, but it has been checked by the massive development of drainage, essentially vertical drainage. The sustainability of irrigated agriculture is now threatened by salinization and the use of poor quality groundwater. Salinity is widespread in the area, ranging from slightly saline to strongly saline patches in most parts of this Doab. In the central and lower parts of this Doab, a considerable area is strongly saline. Moderate salinity is spreading over large tracts affecting agricultural productivity.