Description

1) Over the Top: Technology to Model Wave Overtopping Improves Coastal Resiliency
Kevin Trainor, PE, Woodard & Curran, ktrainor@woodardcurran.com
Co-presenters: Katie Howes, PE, khowes@woodardcurran.com

Abstract: Coastal communities are tackling a myriad of climate change impacts, including extreme precipitation, storm surge, and sea level rise, all of which lead to persistent problems with flooding. On top of that, the development patterns of the past have filled salt marshes or cut off their connection to the sea. While it is common to assess surge and wave conditions on the seaward side of coastal infrastructure, like a seawall, and then assess precipitation impacts on the landward side of that infrastructure, the city of Quincy, Massachusetts is taking a more holistic approach. The City is working in coordination with the Army Corps of Engineers to quantify storm surges and wave overtopping impacts over the course of an extreme event, tailoring mitigation measures more closely to the risk. This approach allows the community to identify opportunities for building resilience in concert with restoring the ecological function of the area’s salt marsh. This presentation will focus on the technology used to map flooding and the inclusion of the EuroTop approach used to incorporate dynamic wave overtopping flows. Presenters will share how the analysis of this area has helped inform projects to reduce incidence of flooding while balancing the goal of re-establishing hydraulic connection of marsh waters to the sea, a critical function for preserving and restoring habitat for native flora and fauna. Attendees will gain insight into how the modeling, data analysis, and projects can be applied in their own coastal communities to improve overall resilience.

2) Flood Analysis Improvements from a Rain-on-Mesh Surge and Rainfall Compound Flood Model
Michael B. Kabiling, PE, CFM, Taylor Engineering, Inc., mkabiling@taylorengineering.com
Co-presenters: None

Abstract: The compound interactions of multiple flood drivers such as coastal storm surge and extreme rainfall events that occur simultaneously or sequentially during a storm worsen flooding in coastal regions. In response to widespread flooding during Hurricane Harvey in 2017, the Texas General Land Office is leading a multi-year river basin study to determine cost-effective flood mitigation and abatement strategies and increase community resilience. This pilot study for the Texas Central Region aims at finding best practices for cost-effective and more accurate coastal flood analysis involving coupling of inland watershed models (e.g., publicly available HEC-HMS and HEC-RAS modeling tools) with coastal models output (e.g., ADCIRC, STWAVE, SWAN, etc.). The pilot study developed a combined HEC-RAS 1D/2D surge and rainfall compound flood model for the Dickinson Bayou watershed—a watershed at high risk for flood related losses and high potential for mitigation action as it ranks first in National Flood Insurance Program flood damage claims relative to the other 57 watersheds in the area. The Dickinson Bayou watershed compound flood model improves the accuracy of hydrologic and hydrodynamic modeling in the coastal areas as it incorporates (a) more detailed topographic and bathymetric data than the Coastal Storm Modeling System (CSTORM) ADCIRC model; (b) bridge/culvert structures, roadways, and levees; (c) land cover and landuse databases derived spatially-varying bed resistance and imperviousness; (d) initial soil moisture and groundwater infiltration; (e) sub-grid numerical schemes for larger model mesh cell sizes and faster computation; and (f) temporally varying gridded rain-on-mesh. The model can also add inland wind forcing to better simulate wind-driven flooding. The modeling simulates well the observed highwater levels for both historical storms Hurricane Ike in 2008 and Hurricane Harvey in 2017. This presentation will inform how surge and rainfall compound modeling can expand and improve flood analysis accuracy in transition and coastal areas.

3) Resilient Stormwater Modeling and Planning for Highly Urbanized Coastal City Watersheds
Swamy Pati, Jacobs, swamy.pati@jacobs.com
Co-presenters: Jason Montminy, Jason.Montminy@jacobs.com

Abstract: This presentation will highlight the Jacobs’ approach in developing comprehensive, sustainable, and resilient master plans for highly urbanized coastal watersheds utilizing the state of the art tools and models and adopting latest climate science. Jacobs is currently adopting in two of the Cities in Florida, including City of St. Petersburg (CoSP) and City of Key West (CKW) . The CoSP Watershed consists of 26 separate basins. Jacobs modeled highly urbanized watershed for floodplain development and to identify BMP projects to mitigate watershed flooding and improve water quality. Models developed included appropriate level of details of urbanized areas with efficient data collection and acquisition efforts to review more than 30,000 structures from stormwater infrastructure files, and 5,000 as-built planset and City’s Atlas Sheets, along with reconnaissance and survey of approximately 3,000 stormwater structures. Water level data logger and rain gauges were installed across the City to collect data for model calibration and verification for most current conditions. Climate science was reviewed to update the current tidal boundary condition for current condition modeling and to estimate 2050 for sea level rise (SLR) and rainfall totals for future condition modeling. Modeling results is being used to evaluate sustainable solutions for flooding and water quality issues with a combination of traditional, non-traditional, and blue/green infrastructure solutions. The CKW is an island City at the most Southern tip of Florida. The City sits close to the sea level and the stormwater drainage relies on the stormwater pipes, gravity wells and pump stations. This planning effort included updating the model with appropriate level of detail based on the new development and topographic information. Climate science was reviewed to understand the impacts of SLR and future rainfall. Future conditions reflecting 30 year planning period used to simulate the models and develop projects to mitigate the flooding concerns.