Review
Managing salinity and waterlogging in the Indus Basin of Pakistan

https://doi.org/10.1016/j.agwat.2007.09.014Get rights and content

Abstract

Waterlogging and salinization are major impediment to the sustainability of irrigated lands and livelihoods of the farmers, especially the smallholders, in the affected areas of the Indus Basin. These problems are the result of a multitude of factors, including seepage from unlined earthen canals system, inadequate provision of surface and subsurface drainage, poor water management practices, insufficient water supplies and use of poor quality groundwater for irrigation. About 6.3 million ha are affected by different levels and types of salinity, out of which nearly half are under irrigated agriculture. Since the early 1960s, several efforts have been made to improve the management of salt-affected and waterlogged soils. These include lowering groundwater levels through deep tubewells, leaching of salts by excess irrigation, application of chemical amendments (e.g. gypsum, acids, organic matter), and the use of biological and physical methods. However, in spite of huge investments, the results have in general been disappointing and the problems of waterlogging and salinity persist.

This paper reviews sources, causes and extent of salinity and waterlogging problems in the Indus Basin. Measures taken to overcome these problems over the last four decades are also discussed. The results reveal that the installed drainage systems were initially successful in lowering groundwater table and reducing salinity in affected areas. However, poor operation and maintenance of these systems and provision of inadequate facilities for the disposal of saline drainage effluent resulted in limited overall success. The paper suggests that to ensure the sustainability of irrigated agriculture in the Indus Basin, technical and financial support is needed and enhanced institutional arrangements including coordination among different federal and provincial government agencies to resolve inter-provincial water allocation and water related issues is required.

Introduction

Irrigated agriculture in Pakistan is mainly confined to the Indus plains where it has been developed by harnessing the principal water resources available to the country. The contiguous Indus basin irrigates an area of about 16 million ha. Under the Indus water treaty of 1960 the total water available to Pakistan from the Indus River system was 181 × 109 m3, approximately 75% of the annual available flow (World Bank, 2005). Of the available water, about 131 × 109 m3 is diverted to the 43 main canal irrigation systems while 11 × 109 m3 is lost in the river system and 39 × 109 m3 flow to the sea (Badruddin, 1996). The total length of the canals, main canal branches, and distributaries is about 57,000 km. The system has 88,600 outlets for the irrigation of service areas. The length of the farm channels and watercourses is about 1.6 million km (Bhatti and Kijne, 1992).

Due to arid and semi-arid conditions prevailing in most of the Indus Basin, the evapotranspiration demand is high and rainfall is scanty and sporadic, limiting productive agricultural systems within the basin to those areas which can be assured of a reliable water supply. Water use efficiencies within the irrigated areas are generally low, with much of the diverted surface water recharging the underlying aquifers. These losses in the upstream of the system have serious consequences for the delivery of surface water to the farmers located at the end of the canal system. However, at the upstream of the system, this groundwater has increasingly been exploited to supplement the surface water supplies, resulting in an increasingly higher system and basin level efficiency (Shah, 2007). However it should be noted at this point that irrigated agriculture productivity remains relatively low (Ahmad et al., 2007).

Over the last decade, the number of private tubewells in Pakistan has taken a quantum jump mainly because of decreasing surface water supplies and incidences of drought. During the extreme drought conditions during 1996–2001, the surface water availability in Pakistani Punjab was reduced by 46%. This led to a 59% increase in the number of private tubewells over the same period (Qureshi et al., 2003). Most of these tubewells were funded by farmers except few community tubewells which were installed by NGOs to provide water for domestic purposes. However, government provided relief to local farmers by exempting surface water fee for the drought period. Due to over-pumping during this period, groundwater table dropped in many areas especially in Baluchistan province which was worst hit by drought. The decline of groundwater table in Baluchistan was up to 2–3 m per year (Qureshi et al., 2004). As a result, groundwater became inaccessible to small poor farmers as they were not able to deepen their pumps and install large capacity power supplies. According to government estimates, the water table dropped to depths that were inaccessible in 5 and 15% of the irrigated areas in the Punjab and Baluchistan provinces, respectively, during this period (PPSGDP, 2000).

Despite improvements in surface water supplies after 2001, installation of private tubewells continued and currently about 0.8 million small capacity private tubewells are working in Pakistan. It is estimated that investment on the private tubewells is of the order of Rs. 25 billion (US $ 400 million) whereas the annual benefits in the form of agricultural production are to the tune of Rs. 150 billion (US $ 2.5 billion) (Shah et al., 2003). The estimated number of users is over 2.5 million farmers, who exploit groundwater directly or hire the services of tubewells from their neighbors. The groundwater is currently providing more than 50% of the total crop water requirements with the flexibility of its availability as and when needed (Shah, 2007).

These tubewells are used for supplying supplemental flows for irrigation and to provide much of the drinking water for urban areas. The total groundwater abstraction from these tubewells is estimated at 45 × 109 m3 against a recharge of 40–60 × 109 m3 (Shah et al., 2003). Out of this, about 33 × 109 m3 is extracted through private small capacity tubewells, which are mostly located in fresh groundwater areas to capture fresh seepage from irrigation canals. The remaining 12 × 109 m3 is extracted by large capacity public tubewells mainly to provide domestic water supplies to urban areas.

The small capacity shallow tubewells (up to 6 m depth) were initially installed by farmers to capture the seepage from unlined canals to supplement irrigation supplies for meeting crop water requirements. Therefore their installation and operational costs were very low and farmers were enjoying their benefits without much financial burden. With the increasing groundwater table depth (>15 m), farmers have to switch from small diesel operated tubewells to high powered electric and diesel engines. Most of the electric tubewells were installed in 1970s and 1980s when government was providing subsidies on the installation costs. Due to increasing energy prices, government withdrew subsidies in the early 1990s, which resulted in stagnation of the growth of electric tubewells and increase in diesel engine operated tubewells. According to recent estimates, only 13% of the total tubewells are operated by electric motors whereas the rest 85% are operated by diesel engines of different capacities2 (Qureshi and Akhtar, 2003). Diesel pumps are preferred by farmers because of their low installation costs as compare to electric tubewells. Other advantages of diesel tubewells include timely availability of water (no power cuts), suitability for farmers having small holdings and fragmented land (due to moveable diesel engine) and non requirement of any reserved money (no tension of monthly bill).

The on-demand availability of fresh groundwater has helped the farmers to cope with the vagaries of the surface water supplies and achieve secure and predictable yields. However, one undesirable consequence of intensive use of groundwater has been the development of secondary salinization. As a result, large tracts of irrigated lands are already salinized and many others are under threat. It is estimated that nearly 4.5 million hectares are already afflicted with this menace, of which about half are located in irrigated areas (WAPDA, 2003). About 30% of this area lies in the Punjab province, which produces more than 90% of the country's total food production. Another 1.0 million hectare is affected by water logging. Of the salt-affected soils in Pakistan, about 40% are saline (containing elevated levels of soluble salts) while 60% are saline-sodic and sodic in nature, which are characterized by elevated levels of sodium (Na+). These serious environmental problems have become a great challenge to ensure food security for the ever increasing population of Pakistan.

Since the early 1960s, numerous efforts have been made to cope with the problems of waterlogging and salinity. These included lining of watercourses to control seepage losses, adaptation of improved irrigation practices and the installation of surface and subsurface drainage systems. Most of these projects were funded by government and no investments were made by farmers. Over the last three decades, considerable work has also been done on the reclamation of saline soils through physical, chemical and biological strategies. Due to its relatively low price, general availability and easy application, gypsum (CaSO4·2H2O) is most commonly used for the reclamation of saline-sodic and sodic soils. During 1970s, government introduced subsidy on gypsum to encourage farmers for the rehabilitation of affected soils. This scheme proved very successful however, these efforts could not be converted into a national program. These efforts remain confined to support on-farm research on salinity and sodicity management. On the other hand, farmers continue their efforts to reclaim salt affected lands through improved water management, crop choices and cultural practices. However these efforts were limited to field scale level and have generally not been taken up by the wider farming community.

Despite huge investment, the success has been limited in solving land degradation issues. The problems of waterlogging and salinity could not be solved as initially envisaged. About 15–20% of the land still suffers from salinity and another 20–30% is confronted with high groundwater levels, from the over application of surface water. Soil salinity problems are particularly serious in the Sind province where some 70–80% of the soil is classified as moderately or severely saline (Smedema, 2000).

This paper discusses the causes and extent of salt-affected and waterlogged soils in the Indus Basin of Pakistan. It also reviews the public and private sector interventions made in the past for the management of saline and waterlogged soils in the Pakistan. The lessons learned and future perspectives of managing salt-affected and waterlogged soils are also the foci of this paper.

Section snippets

Irrigation development in the Indus Basin

About a century ago, Indus Basin Irrigation System (IBIS) was originally designed for an annual cropping intensity (i.e. cropped area per year) of 75% with the intention of spreading water to as large an area as possible to expand the settlement opportunities. The major objective of irrigation development at that time was to prevent crop failure and avoid famine (Jurriens and Mollinga, 1996). Another design feature of IBIS was low management and operational requirements, which is an advantage

Sources of salts in the Indus Basin

Most of the soil salinity in the Indus Basin is inherent, as it was developed during the process of soil formation. The salts are brought in by the rivers and their tributaries. The average annual salt inflow by the Indus River and its tributaries is estimated at 33 Mg. At present only about 27% (9.0 Mg) of the average annual salt flow is washed out of the system while 73% (24.0 Mg) is retained in the Basin, with 13.6 Mg in Punjab Province and 10.4 Mg in Sind Province. Of the salt stored annually in

Extent of saline and waterlogged soils in the Indus Basin

The introduction of a large scale irrigation network without adequate drainage altered the hydrological balance of the Indus Basin. At the time of construction of the network, the groundwater table depth in different canal command areas ranged between 20 and 30 m below the soil surface. Therefore the need for provision of drainage for salt management as a part of the irrigation system was not envisaged at that time. The topography of the Indus Basin is relatively flat and characterized by a lack

Management of salinity and waterlogging through engineering strategies

The threat of waterlogging and soil salinity in the Indus Basin was recognized soon after the introduction of large scale irrigation systems. The first observation wells to monitor the effect of irrigation on the groundwater table depth were installed as early as in 1870. Based on these studies, various remedial measures were tried. These measures included closure of canals in the monsoon season, construction of surface drains in waterlogged areas and lowering of full supply levels of canals (

Future perspectives: Managing the problem—building livelihoods

Despite significant investments, waterlogging and salinity remain as major threats to the livelihoods of millions of poor in Pakistan, and to national food security of the country as a whole which has to produce more food for a growing population. On top of this, the Indus basin is a closing basin, which means that despite the impression that there is too much water in the basin most of it is already being utilized and competition from other sectors is likely to increase. Over the course of the

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