Agriculture is the mainstay of Pakistan’s economy, contributing 24 per cent to its GDP and which in turn is entirely dependent on an irrigation system, comprising a vast net-work of canals originating from rivers and reservoirs.
These reservoirs are important not only for agriculture but also for hydal power generation and supply of water for drinking and industrial purposes. Any depletion in storage capacity of these reservoirs could play havoc with the entire national economy.
Our entire irrigation system comprises of three components: (1) watershed or catchment areas; (2) reservoirs and rivers and (3) command areas (areas irrigated by reservoirs). So ,far only two components i.e. reservoirs and command areas have been under consideration and no serious attention has been paid to the third and the most important component, the watersheds which are sources of water. As a result we are facing serious problems of decline in storage capacity because of siltation and sedimentation.
There are more than 2000 watersheds of over 100 km sq in the country and the rivers flowing from these watersheds, discharge more than 200 billion cubic meter water annually. Due to degradation through over-exploitation of these watersheds, reservoirs are silted up at very high rate. It has been estimated that nearly 350,000 af (acre feet) of suspended sediments enter the lndus river system every year and nearly 200,000 af of sediments per year get deposited in the reservoirs and irrigation channels.
The hilly catchments of the Indus erode between 1000-2000 tons/sq. mile/year, whereas the erosion of the Jhelum and its tributaries rises to 5000 tons/sq. mile/year. The estimated rate of siltation of Mangla Dam is 45,000 af/year which results in the reduction of live storage capacity of 0.034 maf/year. The rate of depletion of storage capacity at the Terbela Dam is 0.160 maf/year which can be a very threatening situation.
There are many factors involved in the degradation of watersheds: natural causes, human activities or the combination of these two often cause watershed degradation.
The natural reasons include geological instability, high intensity, long duration rainfall, and steep river gradients, shallow soils on steep slopes and fire. The human activities include deforestation, unwise logging, repeated shifting cultivation, fuel wood cutting, conversion of forest land to grazing and crop land, inappropriate farming practices, road construction on fragile lands, over-grazing by livestock, socio-economic and institutional problems, etc. To protect the reservoirs from being silted up at high rate and subsequent depletion in their storage capacity we have to find out the solution of watershed degradation problems, some of which have already been mentioned above. First step in this respect is the identification of the cause so that appropriate measures are taken care and inappropriate or ineffective measures are avoided.
Watershed management is no doubt, a difficult task because of its size, extremely heterogeneous nature and most importantly, non-coincidence of watershed boundaries with political boundaries. And yet, the development of strategies and their successive implementation is inevitable. The objectives of managing the watersheds can be obtained by adopting either engineering or biological means i.e. by lunching sound afforestation programme in these regions.
Appropriate planning, design and organization forestry related projects inevitable to reap tangible watershed benefits. Forests and trees affect hydrologic behaviour of a watershed, including the quantity and quality of stream flow, erosion and sedimentation. The lowest erosion and sedimentation rates are usually associated with forested watersheds in natural condition. Stream flow from forested watersheds tends to be more uniform, with low peak flows than those with other ready vegetative cover (grasses, crops etc.). Given this background, the role of trees and forests can be viewed in terms of watershed protection, enhancement of water resources and rehabilitation.
Another main problems with respect to the watershed management is lack of a central authoritative body to execute and monitor all the activities aimed through watershed development. The work can only be exercised effectively when done by a powerful authority. But currently, there, is not a single central organization for the very purpose.
Although, the Dams and Coordination Division (DCD), provincial and AJK forest departments, Small Dams Organization and directorate of soil and water conservation of Punjab agriculture department are engaged in the watershed management activities, these bodies take watershed management as an additional responsibility .and consider it supplementary to their major role.
Therefore dire need is there to realize the necessity of establishing a federal agency having a clear mandate with regard to scientific management of national watersheds, along with providing qualified manpower liberal funds and related resources under ‘appropriate legal authority to impose certain restriction and operation in extreme cases required for the purpose.
A suitably framed central organization should educate, train, motivate the field workers and common local people, in selected areas to be managed. The authority should determine suitable treatments, decide techniques of treatments, coordinate the field activities and enforce laws and legislation to conduct research.