Development of water resources

development of water resources in the syrian desert

The large desert and steppe in the north of the Arabian Peninsula is known as the syrian desert even though only a small part of it is located in the territory of the syrian Arabic republic. not only syria but also Jordan, Iraq, and saudi Arabia possess part of the region for which the Arab centre for the studies of Dry Lands and Arid Zones (ASSAD) is currently preparing a development plan. ACSAD is an independent supra-national with its head quarter in Damascus. it was founded by the Arab League in 1981 and its function is to give the Arab nations advice on matters relating to agriculture and water management, ranging from assistance of specific individual projects right up to advice on the organization of water management bodies. ACSAD is now receiving technical assistance for the Hamand Basin Project from the German Agency for Technical Cooperation (GTZ) and the Federal Institute for Geosciences and Natural Resources (BGR).

Location and topography

The hamand basin has an area of apporaximately 166,000 km, it has lies between 37 and 41 and 30 and 34 N and in he south adjoins the “fertile crescent” which stretches from the Syrian _lebanese- Jordanian levant with Mediterranean features to the mouth of the Euphrates and the Tigris.

The Basin has been an area of transit since Antiquity, crossed by several well developed caravan routes.

Nowdays several pipelines tranverse the area and the well built roads carry a considerable proportion of the transport between the Persian Gulf nations and the Mediterranean zone.

The Survey area has no really pronounced morphological structures. Leaving aside the Jebel el Arab in the southwest which rises to 1400 m, the altitude ranges from 550 to 750 with a slight general slope towards the north east. Shallow, mainly tertiary sediments lie on a crystalline basement which, however, does not outcrop at any point.

Most of the Hamad Basin comes within the sub-tropical winter rains zone. No month of Maximum precipitation which is valid for the entire area can be given because the highest monthly precipitation may occur in November, January or April depending upon the locality in question.

No pronounced lengthy dry periods occurred in the series shown in Fig.2. On the whole, the Hamad Basin has been much less affected by the recent dry periods than the areas south of 15 N. if we compare the precipitation figures for the last 10 years with those of the entire series, we do in fact observe slightly higher precipitation in the very recent past. But this does not hold true for the entire area: the stations in the Wadi Sirhan registered extremely low values from 1968 to 1973, probably because the influence of winter rains decreases and the transition to the tropical summer rains zone with its different natural laws begins at that point.  

In spite of its slope towards the northeast the Hamad Basin can be considered largely a closed inland basin. Only the northeastern area drained by a system of wadis oriented towards the Euphrates. Since, despite very large catchment areas and lengths of several hundred kilometers, these wadis have a relatively small discharge cross section at their embouchures, we must assume that only a few extreme individual floods reach the Euphrates from the Hamad Basin.

Most of the numerous wadis are only slightly incised and usually end in basin and depressions with no discharge. The few discharges which occur periodically in the form of individual floods evaporate in these “khabras” if they reach them at all. Unlike the “sabkhas” in the south of the Arabian peninsula, most of the fine sediments which have only a low salt content so that comparatively rich vegetation can often be found there.

running By far the largest wadi is the Wadi Sirhan on the southwest fringes : this is a 50 km wide fault trough southeast from the Saudi Arabian, Jordanian, frontier for some 300 km where it enters the An Nafud desert.

Groundwater

Limited amounts of recent groundwater are available, especially near the wadis and on the fringes of the khabras. The structures range from simple watering places in the beds of the wadis to brick well which are quite often 100 or more meters deep. Khanates exist only on the northwestern fringe near the foothills of the palmyra ranges. Fossil groundwater, which in some places has already been tapped by deep wells to depths of 1.200m, is also available here and there. These wells are also used to supply some of the cisterns by means of tank wagons.

Vegetation and utilization

 The vegetation diminishes from north to south in line with the annual precipitation. Whereas the northern area is still mainly a steppe landscape, the southern area is almost entirely desert. The plant cover has been seriously degraded by over-grazing in the last two thousand years. Nomadic pasture farming is predominant in the Hamad Basin. Sheep account for some 70% of the livestock and small numbers of goats are also kept. Camel breeding has become less important. Irrigated farming is impossible throughout virtually the whole area : only on the northern fringe is a very small amount of arable farming carried on at some particularly favorable sites, always where sufficient quantities of groundwater are available. Many remains of abandoned settlement projects can be found, especially in the Saudi Arabian part.

Development measures

The objectivities of the Hamad Basin Project

The long term aim of the development project being implemented by ACSAD is to provide a better basis for pasture farming, this also improving the population’s living conditions. Essentially, this requires an improvement in the use of the existing surface water and groundwater resources and the main concept is aimed at intensifying the existing network of wells, thus permitting more regular exploitation of the available pastureland. In this process special care is being taken to insure that the pastureland and drinking water supplies coexist because well developed watering places do of course attract the herds with the concomitant danger over grazing on the immediate and less immediate surrounding land. This is reflected in the nomads ancient wisdom which say that wells spoil grazing.

The basic investigations within the framework of this project have been carried out by the ACSAD staff. The different subprojects recommended by ACSAD will be implemented by authorities of the four countries.

As far as possible, the area’s natural resources are to be utilized, e.g. solar energy for distilling salt water or wind energy for raising groundwater located near the surface.

Improvement and extension of the hydrological observation network  

According to a very simple definition of the WMO, an optimum gauging system should be organized in such a way “that by interpolation between values at different stations, it should be possible to determine with sufficient accuracy for practical purposes the characteristics of the basic hydrological and meteorological elements anywhere in the country.  Yet this principle is subject to both technical and economic limits. In this thinly populated area it is difficult to maintain and repair the stations and to protect them against vandalism. Suitable conditions for establishing stations are found only at a comparatively few places, such as police posts, military camps and pumping stations. As regards discharge gauges the possibilities are even further restricted by the fact suitable hydraulic conditions for taking discharge measurements often do not exist. So the establishment of a new gauging station in these areas in frequently a not entirely satisfactory compromise.

First of all, the existing network was examined to see whether it satisfied certain minimum requirements for defining the situation in the area and as a rough quide for this purpose the WMO gives the following limiting values for such areas the one under consideration :    

Rain gauge stations                        1-7 stations per 10,000 km2

Climatological stations                  1 stations per 30,000km2

Discharge gauging stations          1 stations per 30,000km2

Most of the proposed additions to the network have now been completed. When the present investigation was carried out there were 13 climatological station, which means that with an average of one station per 14,000km the density is more or less twice the minimum stipulated by the WMO. Another seven stations exist outside the area itself and these can also be used for hydrological surveys.

Whereas, on average, the Jordanian part has a station for every 2,200 km2, the density decreases to one station per 10,000 km2 in the Saudi Arabian part. But the stations in Saudi Arabia are very well maintained and fitted with first –class equipment while the value of some of the Jordanian stations is diminished because totalizators are used. Moreover, we can note a concentration along the pipelines and the through roads for reasons connected with the maintenance of the stations and their observations.   

Although the optimum density has not been achieved, viewed as a whole the observation network can be considered adequate for large scale hydrological surveys. Not all the stations are, however, equipped for measuring every necessary climatological parameter, many additional items of equipment are needed. It was also suggested that the 13 existing totalizators should be converted into daily recording precipitation stations or if that was impossible eliminated.

The survey area now contains 6 discharge gauging stations. an water level recorder is operating in the Wadi As Sham which runs from the Jebel el Arab via Zelaf and ends in a large depression. Five other stations are concentrated on the northern fringe where several reservoirs are planned or under construction in the catchment area of the Wadi Hawran in Iraq. All of these stations have only recently been put into operation, only two discharge rating curves are so far available. Another station has now been erected in the Wadi Ruwayshid in Jordan where it crosses the Amman/Baghdad highway near old H 4 pumping station. A further 6 gauges are planned as part of pilot projects, 2 in Syria, 1 in Jordan and 3 in Saudi Arabia. Depending upon the local conditions and the frequency of the expected floods, these are either water level recorders or crest level gauges, each with staff gauges.

Measures for artificial groundwater recharge

The unfavourable discharge conditions are the reason why, on average, only 10 % of the water resources can be utilized in most semiarid regions.  One exception is the North American arid regions where artificial groundwater recharge measures make it possible to utilize up to 40 %.

In keeping with the discharge characteristic mentioned above brief individual floods which infiltrate or evaporate in the Wadi bed itself or in depressions any from of utilization must aim at preventing or at least reducing those losses means of storage operations. In principle, twp possible ways are available :

1.     Storage in retention basins

2.     Artificial groundwater recharge and thus underground storage.

Although efficient management of groundwater is substantially difficult than reservoir losses occur, thus easing the salification problem.

Essentially, the volume of water which can be stored and recovered in any individual case depends upon the available pore volume, the infiltration rates of the upper strata of the soil and the permeability coefficient, and each of these values can be the restrictive factor.  

The procedure to be applied must be adapted to specific conditions in arid regions. Only systems requiring no or merely minimum maintenance can be considered. In view of the large volumes of suspended matter, infiltration wells, infiltration galleries and drainage slots cannot be used since they are prone to clogging. Infiltration basins, which are the most common method in arid regions in California, for example, approximately 40 % of the systems use this principle are unsuitable for the Hamad Basin because reasonable servicing and maintenance are virtually impossible. In particular, no regular removal of the deposited sediment can be expected.

According to preliminary comparative investigations, a combined system of small retention basins and artificial  groundwater recharge operations in the wadi beds is most expedient for the conditions prevailing in the large parts of the Hamad Basin. This method offers a number of substantial advantages.

-         The water does not have to be diverted to the infiltration unit

-         Especially in the upper courses, the wadi beds are usually the areas in which the coarsest sediment is encountered and so the available storage is greatest there.

-         Management is comparatively simple, especially where the wadis are incised in formations with little permeability.

In flat regions and especially around meanders it is possible to divert the water into sandy and gravelly areas near the banks. The drawback to this extensive arrangement is that relatively large dried out areas will have to be moistened before any recharge effect occurs. In such circumstances smallish floods in particular are more or less useless for recharging.

So it is more expedient to install small dams where the topography permits. The retention effect prolongs the infiltration time. If suitable material is available, the dams can be design in such a way that water can spill over them, and a special emergency spillway can be avoided. Nor is an expensive outlet structure required. These very simple and inexpensive barrages act as sediment traps. If properly handled, however, sedimentation must not unconditionally be seen as disadvantage when care is taken to ensure that the fine parts deposited on the surface can again be washed out by the next flood and that only the coarse components remain. Surface water is also available in these basins for a short time during the infiltration phase.

The basins can be arranged so that a body a coarse gravel is systematically built up for direct water storage. This is quite a favourable solution if the wadi bed is cut into the bedrock or into impervious layers or if the water bearing alluvium under the bed is too shallow for underground storage measures. For this solution a relatively low dam is required in the first stage of the project so that fine sediments are washed over the crest and only the coarse sediments are deposited. After the basin has filled the dam is raised in steps of only 1-2 m. therefore the construction requires a relatively long period. To avoid seepage losses not only the dam but also the basin its self has to be made watertight. Construction material for the dams is concrete, rocks or gabions. In the latter cases a sealing is necessary.

The extraction well can be integrated into the dam but even a simple shaft well made of prefabricated concrete