MORE ABOUT THE RECONFIGURED-CHANNEL MONITORING AND ASSESSEMENT PROGRAM
Channel reconfiguration to mitigate a variety of riverine problems has become an important issue in the Western United States. Reasons cited for channel reconfiguration include restoration to more natural or historical conditions, improved water conveyance in flood-prone areas, mitigation of unstable streambed and streambanks, increased sediment transport, and enhancement of riparian habitat or recreational use. Numerous private entities and resource-management agencies have attempted to reconfigure stream and river channels by using designs based on different geomorphic philosophies and classification schemes (Mosley, 1982; Miall, 1985; Montgomery and Buffington, 1993; Whiting and Bradley, 1993; Rosgen, 1996). However, little work has been done in assessing the channel response to and the effectiveness of these modifications over a long period of time (Kondolf and Micheli, 1995). The U.S. Geological Survey (USGS) is engaged in a program designed to monitor and assess selected river reaches that have undergone reconfiguration (Elliott and Parker, 1999).
The objectives of the USGS Reconfigured-Channel Monitoring and Assessment Program (RCMAP) are:
Long-term monitoring of reconfigured channels will enable analysis of how and why a particular reconfiguration design may have remained stable or failed. If a channel modification fails, the analysis will focus on understanding the processes by which failure occurred. These processes could include bank erosion, streambed aggradation or incision, flood-plain deposition or scour, and loss of riparian vegetation through root scour, soil-moisture deficit, or prolonged submergence.
The RCMAP is implemented at two levels to satisfy multiple objectives:
Level 1 - Monitoring Methods and Site-Specific Analysis
Level 1 activities consist primarily of descriptive measurements of channel characteristics prior to (if possible) and following channel modification, as well as geomorphic and hydrologic evaluations of the river reach. These measurements are tailored to a specific reach and entail surveys of the channel cross section and longitudinal profile, measurement of sediment-size characteristics of the streambed and banks (Wolman, 1954), and oblique photography from monumented locations through the reach. Other measurements may include aerial photographic interpretation and streamflow-regime analysis, if photographs and hydrologic records are available.
River reaches are selected for study and inclusion in the RCMAP data base on the basis of the following:
(1) Cooperator interest and funding availability,
(2) The potential for future channel-modification activity in the reach,
(3) The proximity of a streamflow-gaging station, and
(4) Scientific research objectives.
Data are collected over a reach of at least several channel widths in length. A set of measurements are made prior to reconfiguration, if possible, and during the first year after reconfiguration. These measurements will be replicated in a subsequent year to evaluate channel change in the reconfigured reach. The time interval between replicate measurements will be determined partly by the hydrologic history at the monitored reach. Some simple empirical relations also may be used to evaluate potential channel response.
Site-specific analysis provides descriptive information about a reconfigured channel reach in a timely manner and enables interested parties to assess whether the modification activities have resulted in persistent qualities deemed acceptable to land managers and the public. Another potential benefit of the USGS RCMAP is that it enables other agencies or researchers to expand upon and augment the geomorphic data collected by the USGS. Research topics might include hydraulic function of habitat-improvement structures, sediment transport, aquatic habitat, and riverine ecology.
Level 2 - Data-Base Development and Analysis Among Sites
The RCMAP is being expanded to include sites that represent a range of geomorphic, sedimentologic, and hydrologic stream types. RCMAP data are being archived in a manner similar to that of the USGS Vigil Network (Emmett and Hadley, 1968), and these data will be added to this USGS Web site as new measurements are made. The optimal size of the data base for subsequent analyses depends, in part, on the site-to-site variability in the data base.
The Level 2 analyses use the Level 1 data base, compiled over several years, to identify regional patterns or trends in channel processes and morphology and to assess the channel response to earlier modification efforts. This analysis among sites will be ongoing as the data base periodically is updated and expanded. Level 2 analyses identify additional data collection or model applications needed to understand channel processes and responses at specific sites.
Level 2 analyses could include:
Channel adjustments are the expected behavior of alluvial rivers; however, the rate of channel adjustment can range from imperceptible to dramatic and can affect river function and water-resource utilization. The recently monumented channels will be resurveyed and rephotographed, and the sediment will be recharacterized in the future. Replicate measurements will be made to quantify changes in channel geometry and sediment-size characteristics and to determine how and why a particular reconfiguration design may have remained stable or failed. The replication interval will be determined largely by year-to-year streamflow characteristics (recurrence of floods) and the presence or absence of geomorphic adjustment.
Channel modification and reconfiguration projects have been considered for many other river and stream reaches in the Western United States. The RCMAP will include surveys of other recently reconfigured stream reaches and will revisit previously monumented reaches as opportunities arise. Data from new river reaches and replicate surveys at previously monumented reaches also will be added to the data base and subsequently analyzed by the USGS.
FOR ADDITIONAL INFORMATION CONTACT:
Cory Williams, firstname.lastname@example.org, 970-245-5257 x31
Elliott, J.G., and Parker, R.S., 1999, Reconfigured-channel monitoring and assessment program: U.S. Geological Survey Water-Resources Investigations Report 99-4111, 6 p.
Emmett, W.W., and Hadley, R.F., 1968, The Vigil Network -- Preservation and access of data: U.S. Geological Survey Circular 460-C, 21 p.
Kondolf, G.M., and Micheli, E.R., 1995, Evaluating stream restoration projects: New York, Springer-Verlag, Environmental Management, v. 19, no. 1, p. 1-15.
Miall, A.D., 1985, Architectural-element analysis A new method of facies analysis applied to fluvial deposits. Earth-Science Reviews: v. 22, no. 4, p. 261-308.
Montgomery and Buffington, 1993, Channel classification, prediction of channel response, and assessment of channel condition. Report TFW-SH10-93-002 prepared for the SHAMW committee of the Washington State Timber/Fish/Wildlife Agreement, 84 pages plus figures.
Mosley, 1982, A procedure for characterizing river channels. Christchurch Water and Soil Science Centre, Ministry of Works and Development, Christchurch, New Zealand, Water and Soil Miscellaneous Publications no. 32, 67 p.
Rosgen, D.L., 1996, Applied river morphology: Pagosa Springs, Colorado, Wildland Hydrology, various pagination.
Whiting and Bradley, 1993, A process-based classification system for headwater streams: Earth surface Processes and Landforms, v. 18, p. 603-612.
Wolman, M.G., 1954, A method of sampling coarse river-bed material: American Geophysical Union Transactions, v. 35, p. 951-956.