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Newsletter and Technical Publications PART C -- CASE STUDIES Case Study 1: Rainwater Harvesting at Mahassa Area, Syria The Ministry of Agriculture and Reclamation, represented by the General Administration of Irrigation and Water Use, established an institute for integrated studies of the natural agricultural resources in the Syrian pastures at the Mahassa area in Syria, with the goal of preparing an integrated plan for the development of the pastures. This was done in cooperation with many international agencies and organizations, including JICA, IDRC, ICARDA and UNDP. Mahassa is a sub-basin of the Badiya regional basin, located in southeastern Syria. It comprises 55% of the area of Syria, with an annual rainfall varying between 100-200 mm. Its groundwater resources are both limited and essentially nonrenewable. Because of irrational grazing practices that do not take the grazing capacity of the range into account, low rainfall rates experienced over recent years, and extensive cultivation of the arable pasture lands, the vegetative cover of the Mahassa has experienced serious deterioration. The intensive rainfall experienced during the rainy season also causes surface water runoff that aggravates soil erosion problems associated with the deteriorating vegetative cover. The Mahassa basin covers an area of about 42 km2(Figure 55), extending northward from the western series of Palmyra mountain ranges, which rise to altitudes of 880-930 m.a.s.l. The basin is divided into six sub-basins, with areas ranging between 2.13-16.85 km2. The annual average rainfall ranged between 75-90 mm in 1995/96 (dry year) to 156-208 mm in 1996/97 (wet year). The estimated annual rainwater resources vary between 3.3-8.2 million m3. The overall goal of this project is to develop a model that could be generalized for the sustainable development of watersheds in arid zones, to achieve integrated management of water resources, soil and vegetative cover. The primary objective is to develop the Syrian pastures, and to assess the impacts of the various development alternatives on soil and water conservation, erosion control and regeneration of vegetative cover in the watershed. Emphasis was focused on local utilization of rainwater through implementing contour strips, harvesting rainwater for livestock watering, and securing additional grazing lands for use during dry spells. Technology Description To address this situation, a group of technologies were implemented, comprising the following major components:
Surface Water Runoff Reservoirs This component consists of 5 units to store surface runoff for livestock watering. With a design based on geologic and hydrologic data, the units have sloping sides lined with plain concrete. Their capacities range between 2,050-2,900 m3. The selected sites (Figure 55) were located at the end of the feeding tributaries, at their confluence with the main Wadi. The surface runoff is diverted through dikes, with the water being extracted from the units using pumps, primarily for livestock watering. Primary Water-Spreading Dikes Eight earth embankments were constructed, with lengths ranging between 600-2,000 m, and heights between 0.88-1.00 m. The dikes sites conformed to the surface contour lines to avoid water accumulation behind them, and to ensure optimal water spreading. Each embankment was provided with a number of regular trapezoidal weirs to accommodate the highest discharge corresponding to 20% rainfall probability without the construction of a spillway. This was done to avoid collecting the surface water runoff in narrow courses, thereby avoiding soil erosion. Secondary Water-Spreading Dikes These are a total of 60 secondary water-spreading dikes, having trapezoidal sections made of backfill (stone, clay, etc.). The dikes have lengths ranging between 50-100 m, and heights about 0.4 m above the ground level, and were distributed in a manner intended to reduce and spread the surface runoff water, reduce soil erosion, and enhance soil moisture. Collection Embankment The objective of the collection embankment was to collect the surface water runoff that exceeds the harvested water, with the use of reservoirs, terraces and spreading dikes. It has a trapezoidal cross section, and was made of clayey backfill covered with a flood armor layer (length of 600 m; height of 3.6 m). It also had a plain concrete spillway with a sill 20 m long. The embankment storage capacity is 0.3 million m3 (Figure 56). Surface Water Runoff Enhancement Plots Four plots were constructed, with a dimension of 5 x 20 m. Each plot was treated in a different manner to allow investigation of the effect of the enhancement plots on improving surface runoff and runoff coefficient characteristics. Each plot was equipped with stilling basin, collection tank, Parshall flumes with electronic sounders and data collection to measure discharges and the quantities of eroded soil materials.
Figure 55. The Mahassa hydrological basin. detail Terraces The goal of the terraces is to assess the efficiency of rainwater harvest for different contour agricultural techniques for cultivating various grazing plants. The intention is to investigate the effects of spacing between crop contour lines and cultivation methods (galleries, ripper) on soil moisture content. The cultivation lines at the upstream end of the terraces were spaced at one meter intervals. The spacing ranged between 20-65 m. The contour lines were cultivated with four types of grazing plants, including Syrian, American, Salty and Routhah. The experimental terraces covered an area of 80 ha, divided into two equal parts. The ripping method was adopted for the first division, while gallery pitting was applied to the second division. Each division was then divided into three replicas. Three different contour spacings were used for each replica; namely, 10, 20 and 30 m for 4 equal sections, with one type of plants being cultivated at each section. Measurements and readings were collected with humidity and rain gauges distributed over the study area, primarily to test the spacing between the contour lines (10-20-30 m) and to study the contour strips of the slopes (3, 5 and 7%). These structures and earth works were devoted to agricultural research.
Figure 56. Rainwater harvesting at the Mahassa area Application of this technology in its integrated form has great benefits in regard to evaluating different approaches for rainwater harvesting at the same time. The upper foothills of the watersheds have contour terraces. The remaining water resources are collected and spread in the main course of the Wadi, where the water is used to increase soil moisture and facilitate the growth of trees capable of resisting arid conditions. The excess water is also collected in suitable reservoirs built on the tributaries and downstream of the main collection embankment. The main embankment retains the remaining surface water runoff for use in livestock watering. This pioneer experiment in Syria is considered an ideal example of applied research. The results of this research can be used to expand the use of this technology, estimate the quantity and quality of losses in regard to utilizing the wasted water, and improve environmental conditions. There is no doubt that the efforts exerted by the government have a strong effect on the development and spread of this technology. An effective design depends on the availability of rainfall information for long periods. The design must take the minimum and maximum rainfall intensities into consideration, as well as the characteristics of the rainy years. The design of effective embankments, dikes and collection reservoirs also depends on consideration of the proper probabilities in an economically-feasible manner. Extent of Use There are a limited number of such large pilot projects at the regional level, and the existing ones are conducted mainly by the concerned Arab countries. The first pilot project for Syria, for example, is presented herein. The second is at Tenf in the Syrian steppe, which is near the Syrian border of Iraq and Jordan. The design of the Syrian project was implemented via the studies of the Hammad project conducted by the Arab Center for the Studies of Arid Zone and Dry Land (ACSAD) during the early-1980’s. The Tenf project was executed by the Syrian government in the early-1990’s. There are some pioneer experimental projects at the farm level in the Arab countries, an example being the Balamah project in Jordan, conducted by the Arab center (ACSAD) in the early 1990’s. A commonly-used technology in the Arab region is traditional rainwater harvesting. However, this technology is still not widely used on an individual or small-farm scale, primarily because it requires some surveys, studies and structures with high capital costs for regular farmers. An integrated plan has to be implemented to illustrate the economic feasibility of this technology over the long term. In fact, the first obstacle to the widespread of this technology is probably lack of sufficient information on proper design possibilities, as well as lack of needed finances. Operation and Maintenance The operation and maintenance requirements of this project depend primarily on the rainfall intensity and related water runoff, which varies in different seasons. The technology irself operates automatically over the rainfall conditions in the different seasons. The required maintenance includes repair of structures, reduction of soil erosion and removal of silt deposition. The volume of maintenance work is dependent on rainfall intensities. It is clear that maintenance is very important to maintaining the effectiveness and sustainability of this technology, even though it is usually limited to simple manual work at the small-farm scale. The maintenance work should commence before the start of the rainy season, and also after the rainy season when it is suitable for the repair of structures. Level of Involvement The rainwater harvesting technology still receives only limited attention at the farm level, whereas it is increasing on the level of governmental-level agricultural projects. This is attributed mainly to the lack of financial capabilities of the regular farmer for implementing the technology requirements, including data collection, design and execution. In addition, the farmers are not yet convinced of the effectiveness and feasibility of this technology over the long term. This latter problem can be addressed through increasing awareness of the details and benefits of the technology, as well as providing farmers with appropriate technical and design information, as well as access to the needed financial resources (e.g., no-interest loans). The optimal solution to increasing the level of interest in this technology is to find a flexible approach for application of a common sector between the government and the private sector, which can be implemented in remote areas not used for agricultural purposes. Costs The main embankment and the collection reservoirs have collected 116,000 and 643,000 m3 over two consecutive seasons. The estimated initial execution cost totals about 10 million Syrian liras (US$ 200,000). Despite the research nature of this project, it nevertheless provides some financial indications of the feasibility of using this technology. Assuming the initial cost can be recovered in one year, as well as an average annual quantity of stored water of 380,000 m3, the approximate cost for providing water is US$ 0.5/m3. This will be reduced to US$ 0.05/m3 if the initial cost is to be recovered over 10 years. This is in addition to the maintenance costs, which are estimated to be 5-10% of the initial costs (about US$ 10,000-20,000/year, or not more than US$ 0.05/m3.year). Thus, the cost of a cubic meter will reach about US$ 0.10/year, and will be reduced after 10 years to about half of this value. It is noted that these estimates are based on the assumption of average rainfall. The actual unit cost of providing water will decrease in wet years while the maintenance costs will increase. The situation obviously is reversed for dry years. The water spreading along the watercourse for a length of about 5 km and an average width of 0.5 km (i.e., an area of more than 2.5 km2) also has improved soil moisture from 30% to over 100% during November 1996 to April 1997. This is generally reflected in the agricultural product and return. It is noted that each basin or region has its own characteristics and requires its own analysis and assessment. Thus, the proper planning is required to utilize the technology and estimate its costs based on the investment return.
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