Techniques to reduce the duration of flooding-induced turbid water periods in dam reservoirs

ENTRY DATE: 15.11.2013 | LAST UPDATE: 15.11.2013

CATEGORIES:

  • Water Resources
  • Water intake, Purification

TECHNOLOGIES MATURITY:

Ready for application

Technology Owners:

Kyushu Electric Power Co.

Needs Address

The need to mitigate the impacts of increased turbidity in water bodies in areas where rainfall patterns could change due to climate change (particularly, from extreme rainfall events). 

Adaptation effects

  • Reduced duration of flooding-induced turbid water periods in dam reservoirs (reduced quantity of chemicals such as coagulants and chlorine agents used in water treatment processes, and reduced amount of sludge produced by these processes)
  • Improved wastewater treatment capacity to deal with extreme events
  • Securing water resources to deal with water shortages resulting from climate change

Overview and Features

  1. Effective operation of selective water intake facility

    Knowing that clear water forms more quickly in the surface layer of the reservoir, construct upper and lower intakes on the dam, so that when turbid water flows into the reservoir, it can be removed as quickly as possible by continuing water intake from the lower intake. As soon as the clear water has formed, switch over to the upper water intake, allowing the discharge of clear water downstream of the dam.

    Figure: Changes in turbid water inflow into reservoir
    Source: Web site of Miyazaki branch of Kyushu Electric Power Co.
    (http://m.kyuden.co.jp/dam_dakusui_20110)

  2. Protect clear water layer by installing turbid water restraint membrane

    Install a turbid water restraint membrane (vinyl that curtain does not allow water to pass) into the river flowing in, with the aim of protecting the clear water layer in the reservoir from turbid water flowing into the reservoir. 

Cost

Energy source

Electricity

Ease of maintenance

1) Selective water intake facility

  • Perform maintenance according to company policy

(2) Turbid water restraint membrane

  • Generally no inspections are required.
  • Repair when damage or other problems occur.
  • A yard crane is required to lift membrane.

Technology performance

(1) Selective water intake facility

Figure: Selective water intake facility
Source: Website of Miyazaki Branch Office, Kyushu Electric Power Co.
(http://m.kyuden.co.jp/dam_dakusui_201105)

(2) Turbid water restraint membrane

  • Membrane length: 10 to 15 m, Extended: 160 m (20 meters per span, 8 spans)
  • Install boat passage gate in center.

Considerations

(1) Selective water intake facility

  • Measures to reduce periods of high turbidity can lead to greater electricity consumption and costs.
  • Specialized technicians are required.
  • When drawing water into the upper intake, it is important to ensure there is an adequate layer of clear water near the surface to avoid drawing up turbid water from the lower layer of the reservoir. (Kyushu Electric considers about 10 m to be appropriate.)
  • During the switchover between upper and lower intakes, no water can be drawn (in practice, Kyushu Electric has found that about three hours are required)

(2) Turbid water restraint membrane

  • This system may become less effective if flow volume exceeds 300 m3/s. (Actual results vary depending on the site.)
  • If the restraint membrane comes in contact with the river bottom, it may become buried.
  • The membrane may not adjust well to water level variations, as it is secured at both ends. 

Co-benefit, suitability for developing countries

  • Stable supply of water
  • Improvement of water quality 

Information Resources

Miyazaki Branch Office, Kyushu Electric Power Co.

http://110.54.123.73/htsweb100s.aspx

http://m.kyuden.co.jp/dam_dakusui_index