Re‐envisioning stormwater infrastructure for ultrahazardous flooding

Abstract

Ultrahazardous flooding (UHF) occurs on low relief topography at the foot of mountain catchments and is characterized by rapid‐onset, high‐velocity flood flows, large fluxes of sediment and debris, and unpredictable flow paths. 20th century stormwater infrastructure seeks to contain UHF, up to a design level, using combinations of basins, reservoirs and flood control channels. However, these flood control elements may increase the risk of disasters due to: (a) increasingly frequent and intense wildfires that amplify streamflow and debris fluxes beyond infrastructure design capacity; (b) aging and underfunded infrastructure which is susceptible to clogging and failure during extreme events; and (c) expansive urban development where communities are relatively unaware and underprepared for flooding as a consequence of the “levee effect”‐‐the false sense of safety that develops in the presence of flood defenses. 20th century stormwater infrastructure for UHF has also left communities with a legacy of social and environmental challenges including poor water quality, degraded habitats, high maintenance costs, unrealized urban amenities, and altered sediment fluxes. Adopting the Los Angeles Metropolitan Region as a type‐locality for UHF, we propose a new paradigm for stormwater infrastructure based on the concept of erodible flood corridors. Our vision aims for greater sustainability and resilience to extreme events based on congruency with natural processes, conservation of resources and associated ecosystem services, minimization of flood exposure and vulnerability, and avoidance of legacy risk and energy intensive practices. This article is categorized under: Engineering Water > Sustainable Engineering of Water Engineering Water > Planning Water Science of Water > Water Extremes

Stochastic Hydro‐Financial Watershed Modeling for Environmental Impact Bonds

“…The effects of channel hardening are more complex but worthy of consideration. For example, hard bottom channels are effective at managing the risks of flooding and erosion for events that fall within the design capacity of the system but increase the risk of major losses for events beyond the design capacity and create so‐called “legacy risks” such as degraded water quality, negative impacts to ecosystems, and unrealized urban amenities (Sanders & Grant, 2020). Given the central role of LLCW channel erosion in downstream ecosystem degradation, this points to a difficult tradeoff between within‐channel and downstream ecosystem impacts.…”

Barriers and opportunities for beneficial reuse of sediment to support coastal resilience

“…Southern California contains a highly urbanized and energetic coastline with regions of both accretion and erosion under both human and natural influences (Flick, 1993;Hapke et al, 2006;Sanders and Grant, 2020;Vitousek et al, 2017). The region's sediment is fed largely by flashy fluvial input, with the majority of riverine sediment movement occurring during occasional storms (Warrick et al, 2015;Warrick and Milliman, 2003) and both increases and decreases in fluxes as a result of stormwater infrastructure (Sanders and Grant, 2020).…”

Influence of soil characteristics and metal(loid)s on antibiotic resistance genes in green stormwater infrastructure in Southern California

“…In addition to their primary goal of reducing stormwater flows to streams and lakes, GSI systems have many additional ecosystem service "co-benefits", including pollutant removal, promoting nutrient cycling (e.g. carbon sequestration, and denitrification), and potentially fostering habitat protection (Askarizadeh et al, 2015;Grant et al, 2013Grant et al, , 2012, and reducing flood risk (Sanders and Grant, 2020). In densely populated Southern California, runoff from both wet and dry weather is a major source of pollution that significantly impacts the regional water quality and poses risks to local health and safety (Ahn et al, 2005;Ambrose and Winfrey, 2015).…”