9371

• UCREFRP Catalog Number: 9371
• Author: Levee Removal Evaluation Group.
• Title: Green River levee Removal and Floodplain Connectivity Evaluation.
• USFW Year: 1998.
• USFW - Doc Type: CAP-6 LR,
• Copyright Material: NO

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being breached inundation began at 18,500 cfs. At this time, it was classified as a depression. A
350' wide, 4.5' deep section of the downstream end of the levee was removed in March of 1997.
After the levee was breached, the Bonanza site was predicted to function as a terrace but retained
sufficient water to overwinter fish in 1997-98. A high spot in the middle separates the wetland
into two sections at low water levels, a shallow lower section which usually dries up completely
(terrace portion) and a deeper upper section (depression portion). This high spot may inhibit fish
movement into and out of the wetland, as well as increase the distance larval fish would need to
travel to enter the main portion of the depression. The wetland partially fills prior to a surface
connection due to seepage from the river. After connection with the river, backfilling begins and
water levels in the lower depression must rise for several days before water overflows the high
spot and enters the larger section of the Bonanza site. Terrestrial vegetation at the site consists
mainly of tamarisk, Russian olive, and cottonwoods. Hardstem bulrush and cattail dominate
along the shallow areas on the upstream end of the wetland. This site is not likely to overwinter
fish in 1998-99.
Horseshoe Bend
This site is located at RM 285 on the upstream end of Horseshoe Bend on river left. At
13,000 cfs, 18.4 acres are inundated (47 acres when full). Horseshoe Bend was only sampled in
1998 after a 1,000' long, 3' deep portion of the levee was removed in October of 1997. This is
the largest of the eight levee breaches. After connection, two main channels formed at the upper
and lower end of the breach. The majority of the breach remained very shallow. During peak
flows, the Horseshoe Bend site behaved like a side channel with water flowing in at the top of
the breach and out through a channel at the lower end of the breach that exceeded 1 meter in
depth. These deep channels in the breach at the upper and lower end allowed for the site to stay
connected to the river longer than any of the other sites, and allowed for a higher volume of
water to enter the wetland. On June; 9th, when all of the other sites had disconnected or were
draining, Horseshoe Bend still had flow entering the site through the upper channel. The
Horseshoe Bend wetland is located within 100 feet of the river creating one of the shortest
distances for fish to travel to enter the site. High river flows caused sediments to be carried into
the site causing a small delta to forra at the channel connection. This may lead to decreased size
of flooded area over time. The site contains an open area in the center surrounded by flooded
tamarisk. It was originally classified as a terrace but is likely to overwinter fish in 1998-99 and
may need to be reclassified.
I Baser/Chew

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Baser/Chew is a natural terrace, where no removal of levees has taken place. It has been ?.
sampled during all three years of study. Baser/Chew is located on river left at RM 280.8, and
floods at approximately 13,000 cfs. It is much smaller than the other sites and behaves like a
backwater until river flows exceed 16,000 cfs. Above these flows it acts as a side channel, wita
water flowing in at the upstream end through vegetation into the site. Baser/Chew usually dris
up completely by the end of July. `vegetation is mainly flooded willows, tamarisk, and
cocklebur.
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