ICARDA CARAVAN 11

The lessons of introducing technology without considering its potential effects on fragile resources such as underground aquifers in the dry areas are beginning to show in a valley where excessive use of irrigation is harming future prospects for agriculture. 'Sweet' water is starting to give way to brackish water from a nearby salt lake. ICARDA is formulating solutions which will be applicable in similar situations elsewhere.

The salt content of water pumped for irrigation is measured by ICARDA scientists who are monitoring salt intrusion in the Khanasser Valley.

           Typical wells in Khanasser are a combination of a tube well and a traditional Arab well. The typical Arab well has a diameter of 1.25 m and is dug to 5 - 10 m below the groundwater level. At the bottom of the well, a 3 m-high chamber with a 3 m diameter is excavated to serve as a reservoir. Several horizontal channels (daharas) are drilled radially from the storage chamber to increase the rate and amount of water flowing to the well. These daharas, with a diameter of 2.5 - 5.0 cm, can be up to 250 m long. About one meter away from the Arab well, a tube well is drilled. The chamber of the Arab well is then connected to the tube well by a horizontal hole. The pump is located at the bottom of the tube-well. With this system, farmers can pump continuously for about three hours before the collection chamber is empty. It means most farmers can irrigate for up to three hours in the morning and then for another two to three hours in the evening.
          The first irrigation wells were drilled in the Khanasser valley in 1975, but rapid development of wells began around 1990 so that by 1998, 154 wells were being used for irrigating wheat, barley and cotton from the unconfined aquifer. The main driving force for the rapid increase was that farmers wanted to share in the very evident success of the first few farmers to irrigate. Now, these first irrigators complain they can only pump water for about 5 hours a day until the wells run dry, instead of 24 hours as before.
          Pumping capacity in the valley could irrigate about 450 ha, but only around 150 ha was being irrigated in 1998 because farmers could not obtain sufficient groundwater for all the fields they had hoped to irrigate. Even now, more farmers want to sink wells and construct daharas, because the returns from irrigated crops are still, they claim, significantly more attractive than from rainfed barley growing.
           Basin flooding is the only irrigation method used. From the well survey, total water extraction was estimated at approximately 7.7 million cubic meters for the entire valley. During this survey, groundwater levels were measured throughout the valley. (Fig. 1). The water level of the Salt Lake was 314 m above sea level. Valley groundwater levels generally follow the topography.
          Irrigating farmers empty the collection chamber of their Arab wells twice a day on average. This means that a 'draw-down' cone develops around the well that lasts until the well is refilled. This cone is enlarged because of the horizontal holes (daharas) drilled around the collection chamber. As some of these holes are 250 m long, the wells are effectively closer to each other than might at first appear, and the draw-down cones overlap, especially in the central northern part of the valley.
          This causes a regional lowering of the groundwater level, that can be observed clearly in the area between Shallaleh Kbireh and At Shaneh where the water level was below that of the Salt Lake. This low water level causes water from the lake to flow towards the nearby wells. Near the village of Al Hawwaz where cotton is irrigated, the groundwater table is lowered during pumping, but no draw-down was observed. However, during the summer months it is likely that groundwater levels will drop periodically so that water from the Salt Lake can reach the unconfined aquifer. When this saline water reaches the village of Al Hawwaz, it may then flow to the south of the valley towards the lower groundwater levels in Qorbatieh.
          The effect of this salt-water intrusion on the salinity of the valley's water can be measured in electrical conductivity (EC) of the groundwater. An electroconductivity of 1 dS/cm means that about 0.64 g/l salt is dissolved in the water. In the Salt Lake itself, water reached up to 43 dS/cm at the beginning of summer 1998 and the salinity was of the sodium chloride (Na+Cl-) type. Irrigation with water this saline can degrade the soil irreversibly.
          Surveys reveal the tongue of salt water that is being pumped into the valley and used by farmers for irrigation. More tellingly, a farmer near the village of Shreema stopped irrigating his cotton because it would not grow any more.
         Irrigated soils are showing levels of soil salinity, which are at the limit of the salt tolerance of most crops. A 1999 survey by ICARDA showed that the highest accumulation of salts was at 40-60 cm depth, i.e. within the root zone of most irrigated crops. The differences between rainfed fields and irrigated fields are striking, considering that irrigation has only been practiced for a relatively short period.
           The expected potential reduction of crop yields for barley, wheat and cotton, due to salt accumulation in the soil were determined. The figures show that the irrigated soils in the valley are approaching the limits of salt tolerance of the crops grown in the area.
         To protect the quality of the groundwater less water should be pumped in the valley. At the moment work is being done on a groundwater balance of the valley. This will show the amount of groundwater that can be pumped from the aquifer in a sustainable way without encouraging the intrusion of saline water.
           Farmers in the valley are also being encouraged through experimental work to introduce what for them are new crops that consume less amounts of water. These include olive trees and other fruit trees. Furthermore, shrubs that can be used for sheep fodder are being planted to demonstrate how the income from rainfed farming can be increased.
           It is all an integral part of ICARDA's bid to ensure that sustainable food production can thrive in such areas where resources are under threat from the poor management practices of the past.

Robert Hoogeveen is a Consultant Hydrologist with ICARDA.

t's a recurring dilemma for many farmers eager to expand their production. They need to invest in irrigation equipment to drive up their incomes, but the side effects of using that very machinery could make their land unproductive.
        The reason is that good water available for volume irrigation in dry areas is inevitably very limited. Once an aquifer in a low-rainfall area has given up its stored content of sweet water, there is a risk of it being replenished from less palatable sources. This is exactly what is happening in Syria's Khanasser Valley.
        Irrigation is boosting crop yields for now in Khanasser but those growers, who have so far installed pumping equipment, are also condemning their land to a gradual decrease in productivity unless they act now to forestall disaster. The lessons being learnt there from an ICARDA project with local growers will have applications in many similar areas where farmers, who have not traditionally irrigated, also want to increase their yields.

        Pressure on land resources due to increasing population leads to degradation if the carrying capacity of land is exceeded. Without the development of appropriate land-use practices, long-term overuse of land may irreversibly destroy its potential for production.
        However, this does not mean that intensification cannot be used as an alternative way to accommodate increased pressure on the land resources. With this approach, a smaller amount of land is used more intensively, but it is also cared for more intensively. Investments are made to enhance its productivity.
           In dry areas, soil moisture is usually the most limiting production factor. Intensification therefore tends to be based on moisture conservation and irrigation. If the water quality is unsuitable for irrigation, salinization processes are accelerated and can render the land useless for any cultivation after relatively short periods.
         In the Khanasser Valley, about 70 km southeast of the city of Aleppo, farmers are investing in irrigation to maximize returns from their land in the semi-arid area at the fringe of the Syrian Steppe. They use the groundwater from the shallow unconfined aquifer for irrigation. This aquifer is recharged by local rainfall but this is irregular and only between 200-250 mm each year, mostly in the winter months. Excessive pumping can lower the groundwater table significantly, especially at peak irrigation periods. Since the groundwater system in the Khanasser Valley is linked to the Jabul Salt Lake, prolonged lowering of the groundwater table causes salt water from the salt lake to enter the sweet-water aquifer.
           Most households in the valley practice a combination of crop production and livestock rearing. Rainfed farming, with barley as the dominant crop, occupies most of the arable land. However, irrigation farming has developed rapidly over the past 10 years on the most fertile soils in the middle of the valley. Most irrigating farmers practice a rotation with cotton and wheat, and sometimes fallow. The hill slopes and the eastern plateau are used exclusively for grazing.

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