Background:
The City of Sumpter has water rights to divert 15.0 cfs from McCully Creek, a tributary of the Powder River. These water rights date back to 1873. The McCully Fork rights supply 90% of the City’s water use. The diversion is located on National Forest land and the City maintains a Special
Use Permit for site operation. The residents and tourists are dependant on the quantity and quality of this water. In spring the city must deal with flooding and during late summer/fall low flows, it must divert all the water available to operate its diversion.
Limiting Factors to be Addressed
Fish habitat connectivity in a Bull trout designated watershed, sedimentation, flooding, erosion.
Clarification
The diversion is a fish passage barrier due to the concrete drop structure. The lack of fish screening on the diversion fails to enhance fish survivability.
Due to the fact that the diversion inlet is lower than the instream channel, much of the sediment bedload McCully Fork carries is diverted into the filtration system of the current design. The new diversion improvements will allow the natural functioning of the creek to carry its bedload downstream.
Currently the flood plain is not functioning at optimum because of poor design and a diversion structure that is inadequate for the site.
The diversion structure is too small for the site and thus functions inadequately to prevent erosion downstream.
The Sumpter Municipal Diversion Project was designed by Anderson Perry and Associates, Inc. using funds from a previous OWEB technical assistant grant. Staff members from ODFW, USFW, USDAFS, BOR, BVSWCD, City of Sumpter and PBWC sat on a design review committee which provided input to the design and reviewed the design to completion.
The new design provides more efficient means of water diversion by reducing filtering cost to the city, reducing the potential for flooding of the city intake, and improving wildlife habitat along the river with significantly improved fish passage around the structure.
The design calls for the existing concrete diversion structure to be removed and the point of diversion (POD) to be moved upstream approximately 70 feet. A new fish friendly structure will be installed at the new POD. The diversion structure will be a box headgate diversion that utilizes a rock vane weir similar to the ones designed by Dave Rosgen. The box headgate will be located on the edge of the bank with a rock vane installed to act as a weir (see plan view figure). Water diverted will pass through a headgate into a sluice box where water is to be measured using a ramp flume before entering a horizontal flat plate fish screen. Sediment will be removed using a vortex sediment tube located prior to the ramp flume. Water diverted will pass through the flat plate screen into a settling pond located prior to the filter beds. The settling pond will be realigned and resized. Minor modifications will be made to the filter beds to minimize water wasted through the waste channel.
The river channel will be realigned to its historic alignment and four more rock vanes will be added to provide grade control. The realigned channel will be reconstructed to proper channel morphology. An existing overflow channel will also be incorporated into the design. Sill rock will be placed upstream of the diversion in the old overflow channel to prevent cutting during flood events. The access road to the site which passes through the overflow channel will be regarded and rocked to provide additional grade control. The realignment of the channel and incorporation of the overflow channel will reduce the risk of flooding of the settling pond and filter beds.
Project Completion Report
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