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​Flow retention

  A. Background

  1. Retention of streamflow can enhance baseflow. Will that enhancement extend to water supply in the main stem?

  2. A retaining structure slows and widens the stream flow behind it.

  3. The retained water can infiltrate; it also can evaporate and be taken up by plant roots and transpired from leaves.

  4. Infiltration is normal, and its amount depends on permeability of the underlying strata and time over the strata.

  5. Higher infiltration may occur where water is slowed and widened than in the narrower portions of mountain streams.

  6. Evaporation is a function of temperature and exposure to solar radiation and wind.

  7. Transpiration depends on the pond's vegetation environment.

  8. It is greater in a forest-and-shrub than a grass landscape due to greater water uptake and leaf surface area.

  9. That surface area, the canopy, however, may block solar radiation and lower water loss from evaporation.

  10. Can water retention increase habitat resilience at streams without compromising water supply in the main stem?

    Instream | Retention | Beaver

Retention at Barlow, 1.3 mi upstream from outfall


  B. Potential value

  1. The infiltrated water will be cooled and can enhance recharge to stream baseflow.

  2. Streams may be attractive for protection as habitat because they have enhanced baseflow from upstream ponds...

  3. For example, as from a man-made impoundment at Barlow and beaver dams at Stoner, Scotch, and Roaring Forks.

  4. Or have favorable locations where ponding can be established, such as with installation of a beaver dam analog.

  5. Besides an intact dam at Scotch, just upstream is a flood plain with washed-out structures that could be renovated.

    Instream | Retention | Beaver 

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