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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Water Quality and Ecology Research » Research » Publications at this Location » Publication #186412
Title: EMPIRICAL AND ANALYTICAL APPROACHES FOR STREAM CHANNEL DESIGN

Author
item Shields Jr, Fletcher
item COPELAND, R - MOBILE BOUNDARY HYDRAULIC

Submitted to: Federal Interagency Sedimentation Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2006
Publication Date: 4/2/2006
Citation: Shields Jr, F.D., Copeland, R.R. 2006. A comparison of empirical and analytical approaches for stream channel design. Proceedings, Eighth Federal Interagency Sedimentation Conference. April 2-6, Reno, Nevada. Advisory Committee on Water Information, Subcommittee on Sedimentation, Washington, DC, CD-ROM.

Interpretive Summary: Stream channel modifications for drainage, flood control and to address erosion and sedimentation problems have often failed in their intended purposes and have had severe adverse impacts on stream water quality, biological communities, and aesthetics, but there is great controversy about the correct way to design future projects to prevent these problems. The two main approaches for stream channel design, termed the empirical and analytical approaches, respectively, were examined by testing their performance using data from a sand and gravel bed stream in an urbanizing watershed near Baltimore, Maryland. Although the designs produced by the two approaches were similar, they were different enough that computations indicated that the analytical design would probably be stable, but that the empirical design would likely experience rapid erosion. These findings should provide important guidance for regulators, engineers and stream scientists involved in projects involving stream channels.

Technical Abstract: Stream channel design has become controversial, with two main schools of thought. One approach, termed “natural channel design,” features the use of stream classification, design analogs (reference reaches) and empirical relations (regional curves). Natural channel design (or the “empirical approach”) is intended to result in planforms and cross sections thought typical of undisturbed systems, with flow conveyance matched to a “bankfull” or dominant discharge. Explicit sediment transport analyses are typically limited to issues of competence and initiation of motion. The other approach, termed “analytical,” features the use of geomorphic assessments, process-based numerical models and sediment budgets. The analytical approach may be used to produce channel geometries that will accommodate any discharge. Varying amounts of erosion control and sediment management will be required. In fact, both approaches involve some empiricism and both contain certain analytical models. In this paper, differences and similarities between the two schools are further demonstrated in a case study of an alluvial channel carrying a significant load over a movable bed. In this case study the two approaches produce similar outcomes for channel base width and slope, but different channel depths and top widths. A sediment budget indicates adequate performance for the analytical design but likely failure through erosion for the empirically-based design.