Sourcebook of Alternative Technologies for Freshwater Augmentation in West Asia


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<Sourcebook of Alternative Technologies for Freshwater Augmentation
in West Asia>

Underground Structures for Runoff Water Harvesting

Cisterns

This is an artificial reservoir excavated in the frail rocks (calcite and limestone rocks). The depth typically ranges between 3-7 m, with a capacity of 50-1,000 m³. It is usually covered, with smooth walls that are free of cracks and which may be painted with a cemented mortar layer or red clayey paste. Modern cisterns are built or rocks or concrete. The cistern consists of the following parts:

The excavated main reservoir;
The settling basin for receiving runoff water; it allows for the settling of much of the suspended materials prior to the water leaving the main reservoir;
One or more openings in the cistern roof, for the purpose of pumping out the stored water;
Dikes or channels to collect rainwater and direct it to the settling basin.

The cistern is fed from rainwater that falls on residential rooftops, slopes, asphalt roads or flood relief channels, in which part of the runoff water is directed through a tunnel, rock or earth dike from the mountain foothills to the settling basin leading to the cistern inlet. In some cases, Artificial methods are used in some cases to improve the quality of the runoff flow and its conveyance to the cistern.

Hafir

The Hafir (single for “Hafayer”) is an artificial reservoir excavated to different geometrical forms (rectangular. Excavation can be manual or mechanical. Their capacity ranges from 5,000 to more than 1.0 million m³, depending on the conditions at each site. The Hafir consists of the following parts:

The main reservoir, into which the water is collected;
The water inlet structure, generally comprising a settling basin for deposition of the suspended material in the water prior to its entrance to the reservoir, inlet well and piplines for water conveyance inside the Hafir, and with a stilling basin at its end to dissipate the kinetic energy of the flowing water (Figure 18);
A water outlet, including pipelines extending from the inside to the outside of the Hafir, ending with a water distribution well in the form of manual or electric pumps;
Purification units for large Hafirs designated for drinking water supply, including filters and chlorine disinfection units;
Backfill sides, comprised of the excavated material and put around the Hafir to protect it and to prevent residents and animals from contaminating it.

There are several types of Hafir. One type is excavated in the clayey areas, which are naturally impervious. Another type is the lined Hafir excavated in sandy or clayey sand soils. These are lined with impervious material (plastic products, sprayed bitumen layer). The Hafir may be shallow (about 3 m depth) or deep (up to 10 m depth). Large Hafirs that are meant to provide water for large residential communites that secure water requirements for large residential communities consist of two adjacent Hafayer to facilitate their operation, while also reducing water losses by evaporation.

Agricultural catchment ponds similar to Hafir exist in Palestine. They collect the surface runoff flow and mix it with excess spring and well water. They consist of circular or rectangular holes, extending on areas of about 3000 m² and with maximum depths of up to 6.5 m. Their bottom surfaces are lined with plastic sheets covered with a thin layer of protective soil. Their volume ranges between 300-20,000 m³. They collect winter surface runoff for later use for agricultural purposes. They also store excess well water, thereby reducing pumping costs throughout the year.

Figure 18. Feeding a Hafir from a mountain through both its ends

Suitability

As previously mentioned, technologies for harvesting runoff water have been known since the dawn of history, and they are widespread in most of the West Asia countries. There is hardly any country in West Asia that does not use one or more these technologies. Small dams and hill reservoirs, for example, are widespread in Syria, which has about 140 dams constructed to store floodwater, either for storing irrigation and drinking water in areas with high rainfall volumes, or to store water for grazing animals in steppe areas with scarce rainfall. Many dams for harvesting runoff water were constructed in the Mehassa area, within the framework of the integrated development project of the waterfalls in Syria. Five water-collecting reservoirs were constructed, with their sites selected at the end of the side river valleys flowing in the main river valley. A water-spreading dike also was constructed, and an earth dam for collecting runoff water exceeding the harvesting capacity. There also are many water-collecting technologies, such as cisterns, in the Syrian steppe and in Hafayer in the southern region.

These technologies also are widespread in Jordan, with some of them dating back to Roman times (the Roman pools near Madba, Mouker and Petra). Among recent projects, the most important is the Al-Mouker project, in which the runoff water flow is controlled with earth dams, with a storage capacity of about 11,500 m³ for supplemental irrigation. There also is the Saqla project, in which concrete reservoirs were constructed to collect water for supplemental irrigation purposes. Other important examples include the Al-Hammad basin development project, where a number of Hafayer and earth dams wer constructed for harvesting rainwater for livestock watering and for pasture development. In addition to these types of projects, other well-known technologies being used include cisterns, small dams, Mahafir and water-spreading dikes.

Surface runoff water harvesting technology also is spreading in Palestine, especially agricultural catchment ponds. They serve two objectives, including water harvesting and storing excess spring and well water for use at other times of the year.

In Iraq, great attention is given to small dams, especially in the western desert region. In contrast, less attention is directed to Hafayer, spades and streams.

Hill reservoirs and pools, as well as cisterns, are widely used in Lebanon (Figures 19 and 20). Although they are used primarily for irrigation, some also are used for drinking water supply.

Figure 19. Hill reservoir in Lebanon

Figure 20. Hill reservoir in Lebanon (low-flood season)

Water-harvesting technologies also have been known for a long time in Yemen, either in the form of terraces or the construction of small dams (lakes) in micro-watersheds for collecting nad storing runoff water for irrigation purposes in neighboring areas. Floodwater is considered a major irrigation water source in the governorates of Hadramout and Shebouah, where it provides 70% of the irrigation water requirements for the region’s agricultural lands. A water technology called the waterwheel (Saqia), one of the known diversion structures, is used in the Bejan and Doa’an valleys. It consists of a waterwheel inlet and body (Figure 21). Irrigation with this technology is controlled with many traditions and regulations that vary among the different regions. Another technology, known as kariaf (Figure 22) is widespread in the hilly areas of Yemen. It is used to collect rainfall and floodwater from the slopes that surround it. They are either depression basins or large large holes in the land surface, with the water being used for watering livestock. Open reservoirs, called Gawaby, are also widespread in Yemen for collecting rainwater and floodwater. Another technology, known as Al-Shroug, is used in lands formed in natural depressions, where rocks were abraded due to weathering conditions and which receive their water only from direct rainfall (rather than flood runoff). It is widely used in the Hadramout Hill foothills.

In addition to these above-ground technologies, underground structures also are used for water collection (cisterns) in the Hadramout region of Yemen (Figure 23). Called Noqab, they are ground reservoirs excavated to collect rainwater for drinking purposes. Hafayer are also used to collect rainwater for drinking and other domestic applications, and are known as Magel (Figure 24).

Figure 21. Different parts of the channel in Yemen

Figure 22. A large "Karif" for irrigation at Qaidoon, Hadhramout, Yemen

Figure 23. The different parts of Noqab in Yemen

Figure 24. A large "Majel" for storing collected runoff for water supply at Kublanaffar, Jajja

Great efforts were exerted in Saudi Arabia to construct dams on the main valleys. With their number now exceeding 60, they play a major role in securing water for drinking and agricultural purposes (especially on the Red Sea heights). The Hafayer are also commonly excavated in the steppe river valleys to store additional floodwater quantities for use in watering livestock. If they are naturally found in the river valley bed, they are sometimes called streams.

In Oman, small dams are used in the mountains and their foothills to utilize rainwater for drinking water supply and sometimes for agricultural purposes. Dikes are also constructed on the river valley courses to protect Al-Aflaj from being filled with sediments. Agricultural catchment ponds are also used in the Masandam governorate.

Limited rainwater harvesting technologies are available in Qatar. Some Hafayer are excavated for rainwater collection. They are called pools or springs and are used for irrigation. In Kuwait, rainwater harvesting technologies are not popular, due primarily to restrictive climatic and topographic conditions (surface watercourses almost do not exist).

In the United Arab Emirates, many dams were constructed to retain floodwater in the river valleys, mainly to recharge groundwater and for livestock watering.

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