DESERTIFICATION AND RAINWATER HARVESTING
- A network of rainwater harvesting system has been developed spreading over 26,000 sq.km in the Cholistan desert by developing specially design 110 reservoirs with water storage capacity of 440 million gallons.
- Twenty scientifically designed deep tubewells have been installed with annual discharge of about 1405 million gallons where groundwater is usable for drinking of human and livestock population.
- Due to rainwater harvesting system and installation of tubewells now drinking water is available through the year in the desert. Significant reduction of human and livestock migration, resulting saving of Rs. 6 billions annually.
- Developed and demonstrated desertification control technologies over more than 500 acres in the cholistan desert for making desert productive through rainwater harvesting, livestock production, saline agriculture, grassland, range management, arid horticulture etc.
Construction of Model Scientific Reservoirs
The most suitable catchments for water harvesting and collection were identified by PCRWR at Dingarh through contour surveys. Total area of the catchment is 90 hectares (220 acres), out of which 10% is covered by small sand dunes, hummocks and shrub vegetation while 90% is flat, devoid of hummocks and vegetation. The soils of the area are dense, saline-sodic, clayey, impervious, poorly drained having pH more than 9.0, useable as an effective catchment area for runoff. The runoff in the catchment has been increased manifold by developing network of macro and micro ditches. The runoff of the catchment has also been increased by cleaning hummocks and vegetation causing obstacle in the flow of rainnwater. The other techniques e.g. sand stabilization, soil compaction, surface smoothing has also been adopted. All the low lying points in the catchment have been interconnected by ditches. As a result of efforts made to develop efficient catchment, the rainwater is harvested very efficiently for storage in the earth ponds constructed by the PCRWR. To store harvested rainwater, the PCRWR have excavated and constructed seven ponds at Dingarh. These ponds have been designed to catch maximum rainwater within shortest possible time and to avoid maximum water losses. The depth of ponds varies between 4 to 6 meters. The storage capacity of each pond varies between 2067 to 15000 m3. Each pond has been connected with the main catchment through main channel and net work of ditches connecting all lowest points in the catchment via small pond to reload sediments from rainwater before reaching in the main pond. The purpose of channel and ditches is to collect runoff promptly during and after rain.
The main channel and steps in the main pond has been constructed by pucca material. The slope of pond sides is 1:2 to avoid its collapse. The earth excavated has been dropped 16 meter away from the pond banks in three directions leaving front side open to avoid siltation due to water erosion during rainy season. A trench of 1 meter wide and 1 meter deep around the pond away 15 meters from main pond bank has been prepared to catch rainwater and earth coming from earthen bunds. A mini wall of bricks 12 cm high and 7.5 cm thick plastered with cement around the pond close to the banks has been erected to prevent direct entrance of runoff in the pond from banks. The seepage losses from pond have been minimized (1) By keeping bed of pond at the dense clayey layer (2) By spreading good quality polyethylene sheets on the bed of pond covered by 15 cm thick compacted layer of dense clay. The sides of the pond have been plastered with mud. Further, pond after one or two fillings automatically become impervious and seepage losses are reduced. It is because of the fine particles brought by the rainwater from the catchment seal the pore spaces in the bed and sides. As a result of fine material deposition on the pond bed a strong impervious layer of earth is developed, which works like cement plaster. The evaporation losses from the pond have been minimized, (1) By reducing its surface area and increasing the depth of pond, (2) By growing trees as windbreaks around the pond in the multistory form, (3) By erecting earth walls or earth bunds around the pond to function as a windbreak to save pond from shifting sand deposition resulted from wind erosion from the surrounding area.
Water Filter Plant has been constructed by the PCRWR at the pond to filter water to make it drinkable free of mud and other suspended materials to avoid diseases. Good quality water is being provided to the human population on priority. Surplus rainwater is made available to livestock.
Genesis of Rainwater Harvesting Project
The research of Pakistan Council of Research in Water Resources in the late eighties and early nineties showed that clayey soils of Cholistan can be used economically as catchments to bring rain into large deep reservoirs and make it available to thirsty people and animals for the whole year after their filling. These findings plus the obvious hardships of the Cholistanies and their herds during the extreme drought of 1988 to 2004 caused PCRWR to propose a project for “Mitigation of Drought Disaster in Cholistan through Management of Water Resources” (MDDC) to the Federal Government. Recognizing the needs of Cholistanies and observing conclusive evidence that PCRWR knew how to significantly improve Cholistan water resources, the Federal government funded this project.
Objective of the Project
Development of water sources by rainwater harvesting system, pumping good usable quality ground water and desalination of saline ground water in the Cholistan desert where maximum human and livestock population can easily approach for obtaining good quality water during dry and drought period.
A network of water sources has been established by Pakistan Council of Research in Water Resources in the Cholistan desert by developing specially designed 92 reservoirs at appropriate locations normally constructed from 10 to 15 km distances from each other with water storage capacity of 15000 cubic meter (4.0 million gallons) making total of 1.35 million cubic meter (368 million gallons) annually. Twenty specially designed deep tubewells have been installed by PCRWR with discharge of annually about 7.0 million cubic meter (1405 million gallons) in the Cholistan desert where groundwater is usable for drinking of human and livestock population. Two Reverse Osmosis Plants have been installed to desalinize highly saline groundwater with desalination capacity of 0.01 million cubic meter annually for human and livestock drinking. The developed water sources have been distributed in the whole Cholistan desert considering population of human and livestock to meet the requirement of drinking water. The overall drinking water requirement annually for human and livestock population is about 8.0 million cubic meter. Whereas water sources have been developed for providing water at storage capacity more than 8.4 million cubic meter (1800 million gallons) annually. Now drinking water in the desert is available throughout the year. As a result of water source development, migration of human and livestock due to shortage of water has stopped and loss of about Rs.6 billion annually have been saved caused due to reduction in livestock production in the form of mortality, diseases, reduction in meat and milk as well as damage to crops in canal irrigated areas. Further, micro-climate around the reservoirs has also been improved leading to eco-friendly. Now birds and other wildlife can be seen frequently around the reservoirs as well as more and new vegetation species can also be observed resulting overall positive impact on biodiversity of desert.