Rainwater harvesting in the desert of Turkmenistan

Deserts have some of the most varied and ingenious ways to catch and store rainwater. Rain is the only source of sweet water in many desert climates. Groundwater is often saline or laced with fluoride, in addition to being scares. In the extremely dry Karakum Desert in Turkmenistan several techniques have been developed by local people to catch and store rain for human, animal and farming uses.

One such are natural depressions called takyrs. These are characterized by flat or gently sloping topography with clay lining their basins. Takyrs cover 19,000 about sq km. Of this 11,300 km2 is occupied by takyrs that are larger than 1 sq km. These store large volumes of rainfall while the clay reduces water infiltration, providing water where surface streams and aquifers are not available. Collectively, they store 350-450 million cu m per year.

The desert covers most of the country. It is characterized by a warm dry summer and a short winter. Rainfall is usually 110-200 mm per annum during the cooler winter months. Local people have developed different systems to save runoff during the humid periods and survive the long dry season. Though the main activity is cattle herding, households also engage in small-scale farming for home consumption and supplementary feed.

The peculiarities of takyrs make them a perfect surface to store water. Different techniques are used to store the rain for later productive use: soils, shallow aquifers, closed reservoirs and open ponds. The most common are described here.

Khaks are artificial open-air reservoirs that collect water from takyrs during the rainy spells. They are mainly used for livestock for 2-4 months after the winter. They can be used only for a few months owing to the high evaporation rate. The water is unsuitable for human use owing to contamination. It costs USD 350-960 to make a khak depending on the size.

Sardobs are closed cisterns built of lime mortar and bricks with a covering dome. Modern versions are made of concrete. They collect surface run-off and have a capacity of about 500 m3. If more storage is needed, two or more structures are built in series. They are covered so the water is fit for human use. The freshwater can be mixed with brackish aquifer water for livestock for a longer period. These are expensive, and a unit can cost up to USD 8750 to make.

Chirle is another way to store excess water in the sandy soil shallow aquifer underneath a takyr that can be accessed through a well. The rain water is collected in a depression excavated 2-12 m in diameter from where it recharges the permeable sandy layers underneath the impermeable takyr. This small freshwater lens floats above the saline aquifer and it stays separated from the salty water due to its lower density. Wells are dug in and around the depression. The storage capacity of these chirles is flexible. When only one well for human consumption is in use, the structure costs USD 2500. When ten wells are dug, the cost goes up to USD 21,000. If the water is used for livestock or to improve the rangeland the cost rises to USD 36,500. Maintenance costs are relatively low at USD 115-192 per year. The costs are usually shared by many households that use and maintain the chirle.

Oytaks are natural takyr depressions covered with a layer of sandy soil that, during the rainfall, becomes moist and can be used for farming. Fodder is traditionally grown, but they can be used for crops and trees. Oytaks catch gain water from the natural sloping surface of takyrs, or run-off is conveyed through furrows. When plants are growing, oytaks act as sand traps decrease the surface area of the takyr. They are natural so the only cost is of making channels where needed.

Modern takyr cultivation. Parallel furrows are dug perpendicular to the takyr slope to form a series of smaller catchments. At the lower end, a furrow is dug in which the plants are grown. By reducing the catchment area a better runoff coefficient is obtained and the water is used more efficiently. The average distance between furrows is 7-12 m. If the climate is milder even fruit trees and melons can be cultivated using an interspace of 20-25 m. While they need more investment and technological input than the traditional techniques, they are potentially profitable. 

Benefits

All these methods of rainwater harvesting provide freshwater for human consumption and economic activities in deserts. With larger investments, takyr cultivation has the potential for larger-scale desert farming. Optimising local and traditional techniques reduces the expenditure on tanker water or pumping costs.

Herding is the main way occupation. Increasing the local availability of water can improve natural resources. But the downside is animals tend to concentrate around water bodies, leading to the risk of over-grazing and soil degradation. But like has been seen in the case of controlled intensive herding, if animals trample the ground it can help improve soil permeability and mulch.

Return on investment

Takyr cultivation makes farming profitable even in the desert. High Internal Rate of Returns (IRR) have been calculated: 130 for melon production, 38 for quince, 41 for grapes and 30 for pomegranates. Only water sardobs and chirles for human consumption. Sardobs showed an IRR of 14. For chirles with a single well the IRR was 6.9, and when 10 wells where in use it was 8.6. When the water harvesting techniques are used to create new rangelands in the central part of the Karakum, sardobs showed an IRR of 49, chirles of 61 and a small khak of 583. These figures are based on a number of assumptions: all the labor needed is provided internally and no rangeland degradation will take place. In case the water is used to create improved rangelands, the IRR always show positive values that guarantee a positive return.

These examples show how simple techniques with low investments in water harvesting from the natural landscape are profitable. Looking at the cost of water collected with the different methods, khaks appear to be the cheapest alternative in terms of cost of water per volume. Nevertheless, khaks can be used for only a few months per year and they produce contaminated water that is not safe for drinking. Sardobs are the cheapest way to produce safe drinking water. This is particularly true when alternative sources of drinking water are more than 10 km away. The water harvesting systems for productive purpose all have very attractive prospects.

After the breakdown of the USSR, the central state investments in desert development ended and only few new structures has been constructed. There is a large unutilized potential – even in this inhospitable environment – to make more use of the natural harvesting basins. Local farmers associations may play an important role in managing the needed capital and in creating instruments to favor the construction of water harvesting structures.