Flow-through dam for flood-control

ENTRY DATE: 25.12.2014 | LAST UPDATE: 25.12.2014

CATEGORIES:

  • Disaster Prevention
  • Landslide disaster (Hard measures)

TECHNOLOGIES MATURITY:

Applicable immediately

Technology Owners:

National government, prefectural governments, consultants, etc.

Needs Address

  • The need to reduce the impact of flooding in downstream urban areas along rivers 
  • The need to mitigate bore waves reaching downstream areas of a river due to the collapse of a landslide dam during rainfall periods. 

Adaptation effects

  • Reduction of flooding impacts in downstream urban areas along rivers. 
  • Mitigation of bore waves that flow downstream from water overtopping at the dam site, due to the collapse of a landslide dam during rainfall. 

Overview and Features

  • The flow-through dam (also known as "perforated dam") is designed for the sole purpose flood control, just one of the many possible functions of dams. An opening (spillway) is designed into the dam at about the same height as the river bed, so the structure is intended to let water flow through during normal times. This is different from water reservoir function of dams (a water utilization function) (see figure below). 
  • In terms of adaptation, the flow-through dam structure functions to reduce damage to urban areas downstream along the river, by cutting the peak flow of flood waters. Through a similar function, in the case of a bore wave flowing downstream (see note) from the collapse of a landslide dam or due to overtopping at a dam site, the flow-through dam mitigates damage by reducing the power of the bore wave before it reaches the urban area downstream. Note: A bore wave is a phenomenon of a wave surging ahead at a different height than the water level (or water surface). 
  • Because a reservoir dam is for the purpose of water storage, removal of sediment is difficult and there are various environmental impacts such as bad odors due to water quality deterioration. In contrast, the perforated dam, also known as the flow-through dam, has the advantages that sediment removal by heavy equipment is easy to do, and the impact on the environment is small. 

    Figure: Comparison of reservoir dam (left) and flow-through dam (right)(http://www.pref.shimane.lg.jp/kasen/dam/masudagawa/masudagawadam3.data/masuda-panfu-A4tate.pdf)

Ease of maintenance

Because normally no water is stored in a flow-through dam (in contrast to reservoir dam) it is easy to remove any sediment (heavy equipment required).

Technology performance

The scale and performance of a flow-through dam can vary significantly depending on application, location, etc. Below is one example.

Figure: Cross-section of a flow-through dam (example from Masudagawa Dam, Shimane Prefecture, Japan)
(http://www.pref.shimane.lg.jp/kasen/dam/masudagawa/masudagawadam3.data/masuda-panfu-A4tate.pdf)

Considerations

None in particular.

Co-benefit, suitability for developing countries

  • When it comes to building consensus with local residents at the time of construction of the dam, public support/understanding is facilitated by the benefits of disaster prevention and disaster reduction. 
  • No operations are required during regular functioning of the dam, so there is no need for operational technology. 
  • In the future, it is possible to convert this type to a reservoir dam at low cost and over a short period of time, if it becomes necessary to do so due to changes in the supply and demand for water resources, in connection with precipitation changes and the occurrence of drought due to climate change, changes in food demand and lifestyles of residents living downstream, and so on. 
  • The dam does not capture all the sediment, and by allowing it to flow with the current, the amount of sediment accumulating within the dam can be reduced. This is an environmental benefit. 

Information Resources

Masudagawa Dam website (Shimane Prefecture) (flow-through dam)
http://www.pref.shimane.lg.jp/kasen/dam/masudagawa/