Description

1) Case Studies with Rain on Mesh and Integrated Coupled Coastal, Fluvial and Pluvial Modeling Approach in Urban Areas
Rahul Parab, PE, CFM, Dewberry, rparab@dewberry.com
Co-presenters: Ashok Khadka, akhadka@dewberry.com; Michael Hanley, mhanley@dewberry.com; David Bedoya, dbedoya@dewberry.com

Abstract: Dense urban environments such as New York City are subject to flooding from high intensity rainfall events and coastal storm surge. Tropical Storm Ida exposed flood vulnerabilities within New York City’s neighborhoods with extensive flooding in basements and along roadways. Frequently occurring high intensity rainfall events have led to flash flooding in dense urban areas of New England. These pluvial flooding events are exacerbated with inclusion of coastal storm surge and fluvial events (compound flooding). A holistic modeling approach is required to simulate flood vulnerabilities within urban areas such as flooding within basements while integrating coastal, fluvial and pluvial sources of flooding. Dewberry has developed innovative modeling approaches using integrated rain-on-mesh technology across urban areas of New York and Massachusetts. The rain-on-mesh modeling approach allows to simulate pluvial event flows inside and around buildings and structures at varying levels (including rooftops, basements, building interiors, building/pedestrian overpasses, etc.), modeling of spatially and temporally varying rainfall, and modeling of multifaceted green and grey stormwater management systems. A 3-way coupling model with rain on mesh modeling approach allows to simulate coastal hydrodynamics, fluvial and pluvial sources to provide a holistic analysis of flood vulnerability. This modeling approach may help communities develop a better representation of their flood vulnerabilities beyond what is shown on traditional FEMA FIRM maps. This presentation shares case studies highlighting modeling approaches – including a Flash Flood Vulnerability and Flood Mitigation Assessment for the Massachusetts Institute of Technology in Cambridge, Massachusetts, and a 3-way coupled modeling test case project for New York City. The presentation will provide background and context for each of the projects, describe the innovative modeling approaches that were used using variety of modeling software programs, explain benefit of using modeling technique to the project, best practices and lessons learned.

2) Wishing for a Merry Christmas: a Feasibility Study of Christmas Wash and the city’s wishes that they wanted fulfilled. A new approach to flood reduction in Tucson
Zach Whitten, PE, Stantec/STARR II, Zach.Whitten@stantec.com
Co-presenters: Inger Sarappo, CFM, inger.sarappo@stantec.com; Michael Bishop, michael.j.bishop@fema.dhs.gov

Abstract: Christmas Wash is a highly urbanized four-square mile watershed in Tucson, AZ with a dense mixture of residential and commercial properties. The watershed was developed during the pre-floodplain ordinance era and thus was constructed with no flood mitigation measures in place. In July of 2016, a short-duration, high-intensity “microburst” rainfall event occurred over the watershed producing severe localized flooding throughout the watershed. The flooding generated major damage to residential and commercial properties. There have been over 300 flooding complaints recorded within the Christmas Wash watershed since 1994. FEMA with support from the City of Tucson contracted STARR II to perform a feasibility analysis to test flood mitigation project concepts that would potentially reduce flooding hazard and risk to life, health, property, and function in the watershed. Utilizing a watershed-wide hydrologic and hydraulic FLO-2D model, STARRII developed detailed modeling of the numerous concepts. These concepts included storm drainpipe systems, detention basins, road inversion design and green infrastructure. Because this area of Tucson is fully built out, there are physical constraints (i.e. utility, easements, local access) on project design that project team needed to conscious of when developed potential concepts and solutions. This presentation will discuss how the FLO-2D modeling was used to understand how flooding occurs within the watershed and how that knowledge was used to develop flood mitigation concepts that may potentially reduce the known flood hazards. We will discuss how the alternatives were based upon an in-depth discussion with the City of Tucson to ensure the mitigation fit the City's Operations and Maintenance abilities.

3) Better understanding and prioritizing localized flood risk in the flash flood alley of Texas using 2D modeling
Rupali Sabnis, City of Austin, rupali.sabnis@austintexas.gov
Co-presenters: Annabell del Castillo, annabell.delcastillo@austintexas.gov

Abstract: This presentation will review 2D modeling efforts in the Watershed Protection Department in the City of Austin to understand and prioritize localized flood risk in Austin, TX. Austin is in the “Flash Flood Alley” of Texas and experiences frequent flash flooding. Therefore, it is critical to understand the behavior of the stormwater and how it affects the localized flooding. One of the effective tools is the use of 2D modeling with Innovyze’s InfoWorks ICM. City of Austin’s 2D program has evolved over the years, as our understanding of the software and the capabilities of InfoWorks ICM 2D have expanded. The City of Austin is evaluating ways to use the 2D modeling data to assess localized flood risk within the city and prioritize efforts to implement solutions. This presentation will explore the history of local flood modeling in Austin, TX, the current modeling efforts, and the future goals.