Full Spectrum Analytical Channel Design with the Capacity/Supply Ratio (CSR)

Abstract

Analytical channel design tools have not advanced appreciably in the last decades, and continue to produce designs based upon a single representative discharge that may not lead to overall sediment continuity. It is beneficial for designers to know when a simplified design may be problematic and to efficiently produce alternative designs that approximate sediment balance over the entire flow regime. The Capacity/Supply Ratio (CSR) approach-an extension of the Copeland method of analytical channel design for sand channels-balances the sediment transport capacity of a design reach with the sediment supply of a stable upstream reach over the entire flow duration curve (FDC) rather than just a single discharge. Although CSR has a stronger physical basis than previous analytical channel design approaches, it has not been adopted in practice because it can be a cumbersome and time-consuming iterative analysis without the use of software. We investigate eighteen sand-bed rivers in a comparison of designs based on the CSR approach and five single-discharge metrics: the effective discharge (Q eff) or discharge that transports the most sediment over time; the 1.5-year recurrence interval discharge (Q 1.5); the bankfull discharge (Q bf); and the discharges associated with 50th (Q s50) and 75th (Q s75) percentiles of the cumulative sediment yield curve. To facilitate this analysis, we developed a novel design tool using the Visual Basic for Applications (VBA) programming language in Excel ® to produce stable channel slope/width combinations based on the CSR methodology for both sand-and gravel-bed streams. The CSR Stable Channel Design Tool's (CSR Tool) code structure was based on Copeland's method in SAM and HEC-RAS (Hydrologic Engineering Center's River Analysis System) and was tested with a single discharge to verify outputs. The Q s50 and Q s75 single-discharge designs match the CSR output most closely, followed by the Q bf , Q eff , and Q 1.5. The Q eff proved to be the most inconsistent design metric because it can be highly dependent on the binning procedure used in the effectiveness analysis. Furthermore, we found that the more rigorous physical basis of the CSR analysis is potentially most important in designing "labile" channels with highly erodible substrate, high perennial flow "flashiness", low width-to-depth ratio, and high incoming sediment load. The CSR Tool provides a resource for river restoration practitioners to efficiently utilize design techniques that can promote sediment balance in dynamic fluvial systems.

Integrating channel design and assessment methods based on sediment transport capacity in gravel bed streams

“…Soar and Thorne (2001) further developed the CSR approach by incorporating full-spectrum design across an entire flow regime. Most recently, the CSR tool developed for the National Cooperative Highway Research Program (NCHRP) (Bledsoe et al, 2016(Bledsoe et al, , 2017Stroth et al, 2017) broadly embodies ACD concepts while being straightforward enough for widespread use in practice.…”

“…Stable channel design further faces a persistent obstacle of infighting between different stream restoration schools of thought (Lave, 2009, 2012). Natural channel design (NCD) has been widely propagated by practitioners and regulators (Lave, 2012), while analytical channel design (ACD) has been more commonly endorsed by academia and the United States Army Corps of Engineers (e.g., Copeland et al, 2001; Soar & Thorne, 2001; Stroth et al, 2017; Thomas et al, 2002). Although NCD incorporates multiple levels of sediment assessment, practitioners may stop short of performing capacity‐based design due to lack of familiarity with or access to the proprietary FLOWSED/POWERSED software models (Rosgen, 2006), which are also not fully understood by many in the research community.…”

“…We used a modified version of the publicly available capacity/supply ratio (CSR) spreadsheet tool (NCHRP, 2017) to overcome sediment transport myths and misperceptions. Previous research has already provided recommendations about when capacity‐based design is warranted, and the original CSR tool eliminated the need for measured sediment loads while leveraging the power of relative comparison when dealing with analytical uncertainty (Bledsoe et al, 2016, 2017; Stroth et al, 2017). To equitably compare NCD to ACD using the CSR tool, we incorporated sediment rating curves (SRCs) and a bed load prediction model based on specific (unit width) stream power (), both central features of FLOWSED/POWERSED (Rosgen, 2006, 2009), and we tested our modified tool on four gravel/cobble bed streams with measured sediment data.…”

Hydrogeomorphic Scaling and Ecohydraulics for Designing Rescaled Channel and Floodplain Geometry in Regulated Gravel–Cobble Bed Rivers for Pacific Salmon Habitat

“…These approaches often use extremal concepts such as maximizing or minimizing some property such as sediment transport rate to give closure to relationships for channel geometry [89][90][91][92]. Threshold models assume bed material is at the onset of motion, and for a given flow and sediment gradation the continuity, flow resistance, and shear stress equations are solved to develop sets of curves for stable width and slope combinations [93,94].…”

“…An alternative approach is to use the stable analytical method (SAM) to solve basic equations of flow, velocity and sediment transport to determine a range of channel width-depth-slope combinations [105]. While these approaches were limited to a singular grain size and flow discharge they can now incorporate multifractional sediment transport [106] and analyze flow regimes [94]. Similarly, holding gradient constant, cross-section geometries can be optimized for spawning habitat and bedload transport frequency [35].…”