HR: 1340h
AN: H53B-1241    [Abstracts]
TI: The Use of Slope Creation as a Rehabilitation Tool on Regulated Rivers
AU: * Elkins, E M
EM: eelkins@ucdavis.edu
AF: Department of Land, Air and Water Resources, 219 Veihmeyer Hall One Shields Ave, Davis, CA 95616 United States
AU: Pasternack, G B
EM: gpast@ucdavis.edu
AF: Department of Land, Air and Water Resources, 219 Veihmeyer Hall One Shields Ave, Davis, CA 95616 United States
AU: Merz, J E
EM: jmerz@ebmud.com
AF: East Bay Municipal Utility District, 1 Winemasters Way, Suite K-2, Lodi, CA 95240 United States
AB: Channel conditions below dams are degraded by bed armoring, channel narrowing, and channel incision. The last process yields a long-term decrease in slope, as a river's base level is fixed at sea level. Thus, hydrodynamic habitat conditions controlled by slope degrade over time, impacting populations naturally selected for pre-dam dynamics. In this experimental river rehabilitation, it was hypothesized that channel slope below the dam could be increased incrementally, and this increase could then be spread downstream in subsequent years, eventually yielding a reconstruction of the pre-dam longitudinal profile and increasing overall habitat quality. To test the hypothesis, competing experimental designs for the first stage of this plan were created and evaluated for the gravel-bed Mokelumne River in central CA below Camanche Dam using the Spawning Habitat Integrated Rehabilitation Approach. Gravel fill depth was constrained by the monitored 3 ft of incision over 40 years. Alternative designs aimed to maximize bed elevation gain, spawning habitat quality, and habitat heterogeneity, while avoiding bed scour at the test flow of 500 cfs. Using a 2D hydrodynamic model designs with a 3 ft fill were predicted to cause excessive scour regardless of design elements. Iteration yielded the key result that a maximum fill of 1.5 ft could be sustained by notching the upstream riffle to enable excess flow to bypass the spawning area thereby protecting it from scour and providing desirable habitat heterogeneity. Upon placing 2000 cu yds of gravel, riffle-to-riffle slope was raised from 0.001 to 0.0025. Due to project phasing the created slope yielded scour at the end of the site where the bed elevation dropped back to the original level, as predicted. Lower flows than originally expected resulted in gravel exposure. The second phase added another 2000 cu yds of gravel effectively spreading the slope downstream and backing water up to the first site to increase depth and decrease velocity to the desired levels. On-going post project monitoring and analysis is being used to assess slope creation as a spawning habitat rehabilitation tool.
UR: http://shira.lawr.ucdavis.edu
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting