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View Spring 2007 Stream Restoration Networker [pdf]
PHYSICAL MODELING EXPERIMENTS TO GUIDE RIVER RESTORATION
Key elements
Stream restoration physical models, dam removal, gravel augmentation, channel-floodplain dynamics
Overview
Stillwater Sciences is performing the Physical Modeling Experiments to Guide River Restoration (PMEGRR) project with participation and funding from the California Bay-Delta Authority, the University of California at Berkeley (UCB), San Francisco State University, and NCED. PMEGRR’s goal: Use physical experiments and numerical modeling to perform basic research into three problems facing the stream restoration community and to translate that research into usable tools.
Location
Experiments are being performed in specially designed flumes at UCB’s Richmond Field Station.
Experimental context
The California Bay-Delta Authority is supporting a wide range of stream restoration projects in California’s Bay-Delta watershed. Unfortunately, it has found itself hampered by the lack of a strong scientific basis for the use of three widely-used stream restoration methods: gravel augmentation, dam removal, and channel-floodplain reconstruction. Specifically, the Authority found large knowledge gaps in understanding the fluvial processes underlying episodic sediment delivery (dam removal and gravel augmentation) and the response of channel-floodplain geometry to changes in discharge and sediment supply. PMEGRR is addressing these specific issues through:
1. A series of flume experiments that seek to establish the basic geomorphic relationships involved; and
2. The creation of new, or modification of existing, numerical models that translate the basic science into usable form.
Project description
Leonard Sklar, a Principal Investigator and PMEGRR co-Manager, summarized the three concurrent (and interacting) physical modeling threads:
1. Gravel augmentation. Streambeds downstream of a cutoff, or significant reduction of discharge, become armored with the coarsest fraction of the previous bedload. This type of streambed is usually unsuitable habitat, and restoration efforts often address this problem by adding large amounts of finer, more desirable gravel sizes. The approach of this modeling thread is to use gravel augmentation primarily to re-mobilize the armor layer and make the finer gravels trapped below it available again. Experiments to date indicate that this is not only possible but can be accomplished with much smaller quantities of gravel.
2. Dam removal. This modeling thread is closely related to the first modeling thread since it also studies the effects of episodic sediment delivery on the bed, although the size of the pulses is much greater. Research to date has been on studying the infiltration of fines into the bed under various scenarios—a major concern for restoration practitioners since fines fill the interstitial pores in the hyporheic zone, effectively degrading this crucial habitat zone. Experiment results to date indicate that the current assumption (damage to the hyporheic zone increases with pulse size) may not be correct. In fact, the larger pulses of fines may quickly seal the bed preventing further infiltration while still allowing the habitat to function.
3. Channel-floodplain reconstruction. This modeling thread’s first task was to determine how to create a self-formed, meandering channel in a flume in order to study channel-floodplain reconstruction under laboratory conditions. PMEGRR started with a strategy developed by NCED (using alfalfa sprouts in the bank-stabilizing role of riparian vegetation) and created channels that exhibit the right real-world behaviors (lateral migration, alternate bar topology, meander loop cut-offs). PMEGRR hopes to eventually study the effects of different hydrographs on these processes, and the resulting channel geometries, to produce a detailed model of bar growth.
Food for thought
Leonard Sklar shares his thoughts on stream restoration on NCED’s website.
Project website
More information can be found at http://flume.stillwatersci.com. | 
