Next Meeting November 18, 2009

The next Colorado Geomorphology Organization (CoGO) meeting is on Wednesday, November 18, 2009. We will be meeting at 7:00 pm on the campus of the University of Colorado at Denver (Room #3523 in the North Classroom building). John Elliot will be giving a presentation on “River Restoration in Colorado – How Well is it Working?”

Abstract:

In recent decades, interest in the aesthetics, function, and health of riverine systems has led to the development of an industry devoted to river reconfiguration, rehabilitation, and restoration. Many kilometers of stream and river channels in Colorado have been reconfigured by private entities and resource-management agencies by using designs based on different geomorphic philosophies and classification schemes, most notably the Rosgen “natural channel design” approach. The effectiveness of these modifications over a period of time, and the geomorphic response of some of these channels to subsequent floods is being assessed through a long-term USGS program (http://co.water.usgs.gov/projects/rcmap/index.html).
Geomorphic changes resulting from floods in three "restored" western Colorado rivers were evaluated with respect to sediment-entrainment potential and the shear stress generated by observed and hypothetical floods by using a one-dimensional flow model, and by using channel-pattern thresholds based on slope, discharge magnitude, and sediment size. Observed flood-induced changes included local streambed and streambank erosion, alluvial bar deposition, and large-scale reach instability, indicating potential restoration design problems for these reconfigured channels when conveying relatively common flood discharges.
A fourth stream, Muddy Creek, was evaluated with the USGS FaSTMECH multidimensional hydraulic model. Onsite observations after the 2008 peak discharge generally supported FaSTMECH solutions indicating sediment mobility occurred only in limited areas, and predominantly at high and out-of-bank discharges. The limited areas of potential streambed mobility identified by FaSTMECH model simulations and onsite observations since 2001 suggest that the Muddy Creek channel in both reconfigured and control reaches is relatively stable at streamflows up to and slightly greater than the approximate “bankfull” discharge.
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1 Research Hydrologist, U.S. Geological Survey, Water Resources Discipline, Box 25046, MS 415, DFC, Lakewood, Colorado, 80225, 303-236-4882 ext 296, jelliott@usgs.gov