CONSTRUCTING DELAY ACTION DAMS IN BALOCHISTAN
Apr 06 - 12, 2009
Last month, President Asif Ali Zardari in Quetta announced construction of small delay action dams at a cost of Rs 2.5 billion in Balochistan under Rs46.60 billion development package for the province. The check dams or delay action dams are actually built to check the accelerated flow of water for storage purpose ensuring its availability for irrigation year round. These dams have a salutary effect on the groundwater resources, which are inevitable to avoid drought like conditions in a region.
Balochistan is a water-starved and land-rich region in Pakistan. The groundwater tables are on decline due to mismanagement of water resource in the province. Technically the construction of delay action Dams at appropriate points are considered the possible remedy for keeping Karezes (underground water channels) alive. Karezes as traditional system of tapping groundwater for irrigation is practiced in Balochistan for centuries. The system is unique, as it needs no energy to pump groundwater being flowing under gravity. Over the years, however, the system has come under great stress, because of the commissioning of a large number of deep tubewells in the valleys. These tubewells have been instrumental in causing ground water mining and lowering of the water table. The experts argue that delay action dams ensure recharging of groundwater table at different points and impede the course of drying up of Karezes.
In October1988, a study was initiated by the water resource research centre (WRRC) at Quetta through which the hydraulic link between the reservoir infiltration and the karezes that flow downstream the delay action dams, was established. These dams had been constructed by provincial Irrigation Department to replenish the ground-water aquifer to increase the flow of karezes. Two dams, Pechi in Ziarat and Amachbund in Mastung, were selected for study. The study involved the monitoring of flow in karezes, basic data of rainfall, inflow statistics and ground-water level fluctuation in open wells downstream the dams. The infiltration tests were also conducted to establish the infiltration capacity of the reservoir area. Storage draft technique was applied to determine the frequency of obtaining full supply level of dam based on rainfall data from which runoff was computed by developing rainfall-runoff model and with empirical approach. The water balance based on black box technique was used to evaluate the impact of infiltration on groundwater regime.
It was found out that reservoir inflow was not contributing to the flow of karezes. Based on the results of the study, a set of recommendations were made and forwarded to Irrigation and power Department for improvement in the design of the dams. The final report based on isotopic and chemical analysis of water samples stated that karezes were mainly fed by precipitation with short transit time, Hydraulic interconnection between the dam reservoir and the karezes did not seem to exit under the prevailing conditions
Geographically, Balochistan provides highly suitable and favorable conditions and environment for building check dams or delay action dams. There is a high need for river regulation and integrated water resource management, as large volumes of uncontrolled floodwater of non-perennial rivers escape into the sea. The independent experts see an immense potential for construction of check dams or delay action dams on hill torrents in Balochistan. They have marked 120 sites for building check dams in the province, which might be used for power generation and irrigation purpose. The former provincial government had allocated Rs.12 million for building 11 delay action dams on different sites in the province.
Efficient use of irrigation water increases both area and production. Increase in acreage results from saving in water and increase in production from added area and therefore increase in per unit yield and overall good impact on national economy. Fruits are major source of income in areas where water is scarce. Expansion in fruit area is generally constrained by water availability. Trickle Irrigation System has been recognized as a method of irrigation, which provides maximum possible irrigation water efficiency.
The hill torrents in the province bring a substantial quantity of flash floods, which can be harnessed, for the beneficial use. It has been envisaged to analyze the ground-water potential in conjunction with the availability of surface water at different levels of assurances for irrigation purposes to attain optimum water resources utilization. This was achieved by adopting trickle irrigation system and lining of water distribution network to minimize conveyance losses.
The watershed degradation is a problem in Balochistan. It causes decline in groundwater table, rangeland degradation, erosion of Agri- production, flash floods and damage to the standing crops. If watershed is properly managed, the resource will benefit the population and nomads alike. It will provide vegetation for grazing of livestock and fuel wood for the local population. Watershed is rehabilitated through plantation and construction of small earth dams. The watershed management is aimed at recharging groundwater aquifer, rehabilitating rangelands, controlling flash floods and enhancing fuelwood production in the target area. Recently, watershed management activities were carried out at Karak, some 20 km in the west of Quetta valley. Three Earth dams were built and 232000 seedlings planted in the area.
Balochistan is blessed with extensive groundwater resource. The hydrological map of Pakistan shows the groundwater regions, potential, quality, and various hydrological parameters of the province. According to the map, out of total three main hydrologic units, two are located in Balochistan. These hydrologic units are: Indus River basin, Kharan desert basin and Mekran coastal basin. The province enjoys diversity in topography and geology and therefore it is rich in groundwater resources offering best projects for developing groundwater.
Expansion of agriculture and other economic activities in the province will require tapping of groundwater potential of the province. The water table has been declining continuously in the province. The studies suggest the deficit in Quetta sub-basin is about 21,000 Acre Feet per year and that the aquifer storage will be exhausted in 20 years. The groundwater is depleting every year, in some places even with one meter per year especially in the Pishin-Lora Basin. Zhob and Nari river Basins are not available for further groundwater development. The lowering of the water table is a matter of great concern that can have negative effects on all spheres of life.