This weir on Seven Mile Creek does not allow fish to move up or down stream.  A new weir will be constructed that allows fish to travel past this point while still protecting the stream bank and the bridge in the backgroud. - Photo courtesty John Thomas, HCA

This weir on Seven Mile Creek does not allow fish to move up or down stream.  A new weir will be constructed that allows fish to travel past this point while still protecting the stream bank - USFWS photo by Nick Frohnauer

The Columbia Fishery Resources Office is partnering with the Iowa Department of Natural Resources, Hungry Canyons Alliance (HCA), and the Natural Gas Pipeline Company of America (NGPC) to build fish friendly structures on Seven Mile Creek in Montgomery County, Iowa.  The project involves building two weir structures to control a 6.5 foot elevation drop.

The HCA is a non-profit organization that secures federal and state funding to help share the costs of building streambed degradation control structures, like weirs, in 17 western Iowa counties with thick loess deposits.  The HCA and the Iowa DNR  have been working together for several years to find the most cost effective way to control streambed degradation while still allowing for fish migration.  It was determined that structures with a 20:1 (run/rise) slope allowed fish movement over them.  Before a “fish friendly” weir protocol was developed, many sheet-pile and grouted riprap weirs were built with a 4:1 slope which served as an effective barrier to fish movement.  The Iowa DNR and HCA have been working together to replace these structures.

The NGPC pipeline that crosses Seven Mile Creek is at risk for structural damage due to streambed erosion.  NGPC was considering several solutions when HCA presented a proposal to build a weir to protect the pipeline.  The proposed weir would additionally help control further stream erosion and was significantly cheaper than other solutions.  This new weir will be approximately 250 feet downstream from an existing weir.  Using criteria agreed on by the HCA and the Iowa DNR, the existing weir was identified as a prime candidate for fish passage modification.

 The existing weir will be modified to control 3.5 feet of elevation drop.  The downstream NGPC structure will be built to control 3 feet of elevation drop.  The structures will be approximately 140 feet from each other.  The existing weir’s slope will be modified to 20:1 (run/rise) with grouted riprap.  The NGPC weir downstream will be constructed with sheet pile and a 20:1 grouted riprap slope.  Both weirs will have V-notches in the sheet pile and grouted riprap, a maximum of 1 foot high from the center to the base of the banks.  On both weirs, the biggest rock will be randomly placed in the center third of the channel.

The weir project will open up an additional 4.1 miles of stream and benefit a variety of native species including: flathead chub (species of concern), channel catfish, bullheads, bluegill, largemouth bass, crappie, and numerous non-game species.

Working with partners to construct new weirs and replace fish barriers with structures that allow fish movement helps promote the Service’s goal of working with partners to identify and provide access beyond barriers to fish migration.