Ecological design of multifunctional open channels for flood control and conservation planning

Abstract

Historically, typical open channel flood control systems have been designed for a single function: to enhance human safety by preventing flood damage to human landscape infrastructure. This single-purpose objective is increasingly an untenable practice. Because river systems in human-dominated landscapes often play important conservation roles for biota (e.g. endangered species), it is important that flood control planning be integrated with conservation planning principles and goals. ‘Regenerative design’ seeks to intentionally enable an environment to continually replace ecosystem structures through natural processes, which is a design paradigm that can achieve multiple socio-ecological goals. In river systems, flood control channels need to be multifunctional where feasible, and be designed to accommodate vegetation as well as geomorphic processes, such as meander dynamics. A heuristic analysis of three areas from California's existing but antiquated Sacramento River flood control system (including two bypass channels) was used to illustrate these concepts with a series of expansion scenarios for each channel. Minimum dynamic area was gamed (by expanding the average channel width and adjusting Manning's n roughness coefficients) in the main channel (river miles 84–144) to more than double the existing conveyance, which resulted in nearly quadrupling the roughness coefficient allowing for increased riparian vegetation. The bypass channel widths and roughness coefficients were also gamed to achieve 100- and (alternatively) 200-yr flood protection while providing increased potential for riparian vegetation and flood refugia for terrestrial animal species. These scenarios conceptually illustrate that expanding the flood channel footprint while increasing design roughness coefficients can effectively meet multifunctional objectives.