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Approaches and experiences in ephemeral stream flood control and the performance of the floodwater spreading systems on aquifers
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ALIREZA ESLAMI *   , Aliakbar Abbasi |
| AREEO & Kanrrc |
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Abstract: (30 Views) |
| Considering the climatic situation and the conditions governing Iran's water resources, using seasonal runoff and floodwaters is one of the most important solutions for adapting to water shortages and reducing climate risks. It is of particular importance to control and direct seasonal floods, prevent possible damage, and restore vegetation cover through runoff absorption and recharge of groundwater aquifers. In this regard, utilizing valuable local experiences in flood exploitation and combining them with up-to-date science, including implementing FloodWater Spreading System (FWSS) on aquifers in ecosystems coupled to groundwater, can play a special role in designing and completing good flood governance. In this article, various methods of floodwater spreading on aquifers (11 selected plans) and the technical dimensions of their main components from a practical perspective, in addition to the advantages, problems, and causes of weak system efficiency, have been studied and analyzed. Investigation of the performance of the systems under study shows that in the direct water intake method (without a diversion dam or lateral intake), the problem of sediment load entry seriously affects the efficiency of the system. However, if flood control operations are carried out with a diversion dam or appropriate water Intake structure (similar to the Kashmar aquifer system), the problem of sediments and reduced channel transfer capacity will be reduced to some extent. If the suspended sediment load of the river or ephemeral stream is high and provisions such as the design and implementation of sedimentation ponds are not foreseen, this will result in sedimentation in the channels and the spreading area, as well as a decrease in the permeability of the spreading area. Therefore, to overcome the problem of sediment load entering the system, it is doubly necessary to pay attention to appropriate flood control locations and related design principles, as well as principled implementation operations, especially where the method of flood control is indirect and through the diversion of a stream from a river. In this regard, the Turky-nest structure has been implemented in some systems, including the Gonabad aquifer (phase one) and Sabzevar. Although the role of this type of structure in these systems, in addition to being a sedimentation pool, is to store and then direct the flood to the main channel and the spreading area, due to the high sediment load, they practically lose their effectiveness after several flood events and require sediment discharge and repair of the constructed buildings. From the functional aspect of the structures, examples of scours that occurred downstream of the Drops in the Kashmar aquifer and the flow Gates in the Sabzevar aquifer indicate an inappropriate number of Drops and an inappropriate design of the relaxation Stilling pool downstream of the Drops and Gates. Various structures used in FWSS, such as river Intake structures, slope adjustment structures in the water supply channel, and Gates used to safely pass flow from the distribution area upstream of an embankment to the distribution area downstream of an embankment, if not properly designed and implemented, can be completely or partially destroyed, compromising the entire performance of the FWSS. Considering the flood events in these years, the performance of the systems under study shows that in the downstream areas of alluvial fans that have micro-channels, the method of spreading the flood through the expansion channel and the spreading edge is not effective. Since the technique of controlling and directing the flood in this method will cause the flow to concentrate in erosive points and destroy the system components and the uniformity distribution floodwater. On the other hand, in areas with suitable topography with low slope and no micro-channels (such as the FWSS on the Jajarm aquifer), flood spreading systems through the spreading edge perform successfully. |
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| Keywords: Floodwater, Drop, Aquifer, Floodwater supply Channel |
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Type of Study: Research |
Subject:
Special
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