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In the United States, there are approximately 84,000 dams, impounding 600,000 miles of river. Dams and reservoirs are constructed to provide water to places that have either an insufficient amount of water or none at all. They are also built to store water or use water for hydropower. Among the essential reasons for dams is their critical role in flood control.

Detention Dams
Detention dams are dams constructed to prevent floods or reduce flash flooding. These dams are effective in regulating water levels of rivers by storing the flood volume in a reservoir. This flood water can then be released later when the water levels go down. For every one of these dams, there is an integrated management plan. Such plans are effective in preventing the loss of life and property since the water is released in a controlled manner to the river below the dam or diverted for other uses.

Flow-Through Dams
Flow-through dams are constructed to control floods and flood risks in downstream ecosystems and communities. These flow-through dams are essential to maintaining the infrastructure and protecting people’s livelihoods in flood-risk areas. It is customary for local decision-makers, planners, and engineers to be involved in the construction site choice, along with the spillway, wall height selection, and the location of the desired river flow rates and carrying capacity of the dam. Consideration must also be given to ecosystems and local communities to prevent adverse impacts.

Flow-through dams require general maintenance and periodic clearing of sediment and debris. This clearing permits optimal water flow that prevents significant damage to urban areas downstream. If this work isn’t done regularly, it can put those downstream of the dam at a greater risk of flooding. Such clearing reduces the power of waves that may surge ahead above the water level. Flow-through dams that are sometimes called “perforated dams,” can prevent landslides since they cut the peak flow of floodwaters. An opening called a spillway is made in the dam at almost the same height as the river bed, allowing water to flow through. While flow-through dams, sometimes called “perforated dams,” effectively protect flood-risk areas, they can also help reduce the expense of post-flood reconstruction. These dams also preserve fish migration routes and provide recreational benefits.