9641

• UCREFRP Catalog Number: 9641
• Author: Hedrick, T. N., K. R. Bestgen and K. D. Christopherson.
• Title: Entrainment of Semi-Buoyant Beads and Razorback Sucker, Xyrauchen texanus, Larvae into Flood Plain Wetlands of the Middle Green River, Utah.
• USFW Year: 2009.
• USFW - Doc Type: C-6/RZ-ENTR,
• Copyright Material: NO

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entrainment of flows and sediment, deposition of sediment as flows recede, and scouring of

breach sediment occurring the following year that would then move into the flood plain itself.

Even single downstream breaches have been shown to accumulate sediment over time (Birchell

et al. 2002; LaGory et al. 2003). Filling of wetlands in the flood plain is a natural process of the

riverine ecosystem; the question to consider is whether managed Green River wetlands are filling

at rates that are unacceptable.

Although we did not see high flow or bead entrainment in single-breach wetlands, there

may be opportunity to improve entrainment at these sites. Heitmeyer and Frederickson (2005)

make a number of recommendations to the Ouray Refuge to improve flooded bottomland habitat

and connectivity to the Green River within the refuge. Their recommendations are based on

historical notes that flood plain wetlands within the refuge would flood first via "low elevation

sites along natural levees at downstream ends of the wetland and last at higher elevation point

bar surfaces on inside bends ofthe river." They refer to flooding from the downstream end of

the flood plain as "backwater" flooding. There are multiple morphological benefits of backwater

flooding: reduced sedimentation of entry sites, reduced scouring of exit sites, better retention of

nutrients, and promotion of cottonwood regeneration through deposition of fine silt. This

moderate amount of silt will also increase flood plain productivity. These downstream breaches

are not similar to the one located at the Stirrup flood plain (long and narrow); instead, they

recommend widening the 61 m breach (width measurement) at Johnson Bottom and constructing

an additional downstream breach also at least 61 m wide. A wider breach or multiple wider

breaches will likely behave differently than a long, narrow one and may allow for increased

entrainment at least during ascending flows when water is moving into the flood plain.

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