Semi‐automated hydraulic model wrapper to support stakeholder evaluation: A floodplain reconnection study using 2D hydrologic engineering center's river analysis system

Abstract

Floodplain reconnection projects are largely nature-based solutions that have great potential to restore channel stability, attenuate stormwater, improve flood resilience, and improve water quality. The suite of possible restoration options for a given study area must consider the multiple uses and functions of river corridors, along with the potential impacts and benefits to adjacent infrastructure. Therefore, decision-support frameworks designed to help stakeholders compare floodplain reconnection scenarios to best meet site-specific design objectives are needed. A River Scenario Evaluation Tool (RiverSET) was designed in Python as a wrapper around a two-dimensional hydraulic model (2D Hydrologic Engineering Center's River Analysis System, 2D HEC-RAS) to guide an alternative analysis of various floodplain reconnection techniques. RiverSET runs each reconnection scenario in sequence and extracts the values needed to evaluate scenarios at user-defined regions of interest. The results of these evaluation parameters (depth, duration, stream power, percent time inundated, and velocity) are compiled and displayed for review and synthesis. RiverSET's utility is demonstrated here through a case study on the Black Creek in Vermont, United States, involving five floodplain reconnection scenarios and a variety of stakeholders.

Terrain‐derived measures for basin conservation and restoration planning

“…In the study area, floodplain restoration for floodwater, sediment, or nutrient storage would likely be most effective downstream of reach M17 (greater than approximately 90 km 2 of drainage area). Reaches (i.e., M05, M19A, M19B, and M20; see Supplemental S.9) with SSP‐flow curves that exceed critical SSP Thresholds at small design floods such as the Q5 (e.g., Figure 6, Note 1), may be good choices for restoration projects either at the reach itself or in upstream reaches to attenuate peak flows and dissipate flood energy and erosion/incision hazard (Gourevitch et al, 2020; Morris et al, 2005; Rijke et al, 2012). Reaches (i.e., M06, M08, M11, M13, and M15) that have large DSVC accessed at small design floods or have CSVC accessed only at moderate design floods (Figure 6, Note 2) may be good choices for channel reconnection (e.g., berm lowering or removal; installation of cross‐culverts beneath roads) (Morris et al, 2005; Worley et al, 2022). Reaches with large CSVC that can be accessed at small design floods (i.e., M05, M08, M10, M11, M12, and M16) may be most suitable for conservation easements.…”

“…To illustrate our framework, we chose the Mad River watershed located in central Vermont (Figure 1), due to the abundance of prior work related to stream geomorphic conditions and processes (Ross et al, 2019; Worley et al, 2023) and the availability of a well‐calibrated 2D HEC‐RAS model for assessing our low‐complexity model results (Seigel, 2021; Worley et al, 2022). Elevations in the Mad River watershed range from 132 to 1245 m above sea level.…”

“…To evaluate whether the assumption of normal depth flow conditions affects SSP estimation, we benchmarked the SSP calculated from probHAND using a calibrated two‐dimensional Hydraulic Engineering Center's River Analysis System (HEC‐RAS) unsteady model of the study area (Seigel, 2021; Worley et al, 2022). We ran the HEC‐RAS model for 2‐, 25‐, 50‐, 100‐, and 500‐year design events (Q2, Q25, Q50, Q100, and Q500) and exported rasters of SSP for each event.…”

“…3. Reaches (i.e., M06, M08, M11, M13, and M15) that have large DSVC accessed at small design floods or have CSVC accessed only at moderate design floods (Figure 6, Note 2) may be good choices for channel reconnection (e.g., berm lowering or removal; installation of cross-culverts beneath roads) (Morris et al, 2005;Worley et al, 2022).…”

The role of rewilding in mitigating hydrological extremes: State of the evidence

“…These variations reflect the moderating influence of factors such as event magnitude (e.g., Garcia‐Ruiz et al, 2010; Cruise et al, 2010) the scale of landscape change or intervention (e.g., Škute et al, 2008; Ward et al, 2008), vegetation characteristics (e.g., species; Fahey & Jackson, 1997; Murphy et al, 2021 and maturity; Viola et al, 2014), antecedent conditions such as soil moisture (e.g., Ghimire et al, 2013; Hughes et al, 2020), catchment size (e.g., Deutscher and Kupec, 2014) and legacy effects associated with the landscape history (e.g., Ahiablame et al, 2019). Only 3% of high flow studies showed no change or negligible change, attributed to physical characteristics at the catchment scale (O'Donnell et al, 2011) and site or valley scale (Worley et al, 2022). Interactions between multiple environmental factors created a combination of increases and decreases in flood risk for some publications: 11% reported variable outcomes spanning attenuation and increased peak flows within the same study.…”