Strentzel Meadow Enhancement

Abstract:

This project would do three things: (1) enlarge and level the collection swale at the bottom of the meadow to slow down the water and enhance sediment drop-out, as well as to provide additional capacity; (2) install three upstream trash racks to catch and divert debris onto the constructed floodplain and by doing so prevent future obstruction at the outlet structure;   (3) construct an interceptor channel to re-capture the bypassing flow and route it back to the meadow.

Purpose: This project will enhance an existing restoration/water quality/flood protection project to enhance its ability to perform these functions and to adapt to developments brought on by the 2005 New Year's Eve storm. The project held up well in the storm: dropped out sediment to improve water quality and protected the neighborhood from flooding with one exception. This exception was caused by debris accumulating on the trash rack which backed up water sufficiently to briefly overtop a berm and flood one garage and one outbuilding. The high stormwater flows also caused severe erosion, landslides and downcutting in the Strentzel Creek channel upstream of the meadow. The severe erosion provided much of the sediment that came into the meadow. The downcutting provided access to a sub-surface route for a portion of the stream flow to escape the channel and re-appear in a horse paddock and flow to Alhambra Creek without passing through the meadow. This project would do three things. (1) It would install grade-control structures to slow the water and adjust the size of the channel to more closely approach bankfull size. This adjustment will increase sediment drop-out and debris-stranding on the floodplain. (2) It would enlarge and enhance the collection swale at the bottom of the meadow to prevent plugging the outlet by improving debris removal and sediment drop-out away from the outlet. Both of these actions would improve water quality and reduce flood risk. (3) It would construct an interceptor channel to re-capture the bypassing flow and route it back to the meadow. This would would help improve water quality by providing an opportunity for nutrients in the flow to be absorbed in the meadow. This channel will also demonstrate the feasibility of returning the stream to a more natural location away from the actively eroding hillside.

Keywords:

Watersed Management Strategies:

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