Dams

Underground recharge dams

The rate of evaporation is several times higher than the rate of precipitation in arid and semi-arid regions. In such circumstances, surface storage is not feasible due to the high rates of evaporation, and hence the idea of storing rainwater underground. Industrial underground recharge is done with the help of injection wells, underground recharge dams, or artificial recharge basins. Despite the novelty of the idea and concept of groundwater recharge, it found wide and rapid acceptance, as several dams for groundwater recharge were constructed in various countries of the world.

Basic rules for the construction of dam

Dams are built on the streams of the valleys to store water in times of floods, and then it is allowed to flow slowly to feed the thick sedimentary layer behind the dam. It should be noted that groundwater recharge mainly occurs at the bottom of the valley in relation to the dam, and not in the assembly lake itself, contrary to what some believe, as the lake floor quickly becomes covered with a mud layer that prevents leakage, and since groundwater recharge in this area becomes Useless, the water that is allowed to flow out of the catchment lake easily seeps into the gravel aquifers further down the slope of the dam.

Dams are designed according to the flow rates of the valleys so that the water flowing from the openings of the dam can leak into the sedimentary layer located at the bottom of the dam. Storing a quantity of groundwater of ten million cubic meters if the groundwater level rises by only one met.

The ingredients

Storage lake: In relation to the nature of the Sultanate's topography, the storage lake with groundwater recharge dams is usually of a relatively small capacity. It is worth noting that the prevailing trend at the present time is to design storage lakes that can contain the flood waters that occur every five to ten years on average. The average height of groundwater recharge dams in the Sultanate is estimated at 10 meters, and the average length of the top of the dam is estimated at about 3.5 km, and the average storage lakes at about 4 million cubic meters. The dam can store more than 4 million cubic meters per year, and the water storage period in the lake is usually less than Fourteen days.
Construction materials: The types of dams are determined mainly in the light of the construction materials available at the site. In the Sultanate, earthen dams constructed of sand and gravel are spread over a wide area. An example of this is the Tanuf dam, which was designed to drain water at very high flow rates from a narrow spillway, as it was constructed from A gabion with an impermeable layer of asphalt at the up-slope side and a concrete spur at the bottom of the slope with a calming basin to dissipate water energy.
The spillway: It is that part of the dam that is designed to safely drain the flood water. The spillway is designed to drain the surplus water over the dam body. The surpluses of groundwater recharge dams in the Sultanate should be of a large capacity, as they are often found in the lower impoundments of the valleys that descend from relatively large drainage basins. Therefore, rapid flooding in these conditions results in very high peak flows. It was taken into account in the design that the largest part of the dam be a spillway, in order to ensure its safety from flood risks, and it also helps to spread water over a wide area below the dam and thus increases ground recharge operations in those areas.
Protection from floods: Most of the dams in the Sultanate are characterized by their relatively small size, as they were designed to accommodate the flood waters that occur once every five or ten years on average. Less effective in reducing the risks of those rare floods. It is less effective in reducing the risk of those rare floods.
Monitoring: The importance of the hydrological monitoring network of dams is shown to determine and know the volume and quantities of water that reach the dam and the time of its arrival, to evaluate its effectiveness, to put in place safety measures, to draw conclusions and to use them in the construction of new dams. Therefore, the groundwater recharge dams were provided with the necessary devices and equipment. The hydrological network of the dams includes 47 stations for measuring rainfall, 18 stations for measuring the flow rate of aflaj, 31 stations for measuring the flow of valleys, and 264 wells for monitoring groundwater. By studying the data records of these stations extensively, it was found that the total quantities The water retained by feeding dams throughout the Sultanate is slightly larger than the total capacity of those dams, and this amount currently amounts to about 84 million cubic meters.

Surface storage dams

Due to the lack of surface flow water and the high percentage of losses from evaporation in some regions of the Sultanate, the benefit from storage dams is considered limited in the Sultanate. A dam for surface storage in mountainous areas to meet the needs of the population in these areas.