Case Study

The first state-wide flood planning program

Texas Water Development Board accelerates the development of the first state-wide flood planning program in the absence of publicly available flood data

The Problem In 2019, the Texas Legislature tasked the Texas Water Development Board (TWDB) with delivering the first-ever state-wide flood plan for the State of Texas.

This project was led by Reem Zoun, the Director of Flood Planning, and Director of Flood Science and Community Assistance, Saul Nuccitelli. 

In 2020, fifteen regional planning groups were formed and they worked together on the mission for a statewide flood view by bringing together sets of regional flood plans. To enable the regional flood planning groups in their efforts the TWDB gathered together various flood-related data in a Flood Planning Data Hub

The group identified and compiled comprehensive flood hazard data for each region based on the best available information. This informed a plan to develop a “flood quilt” of data taken from a variety of sources including federal and state flood risk data, natural flood hazard layer datasets, base-level engineering (BLE), and digitized paper (FIRMS). 

However, there were gaps in the publicly available data as approximately 63 counties did not have any existing flood maps. 

The solution Where regional flood data was outdated or unavailable the TWDB worked with contracted engineering firms to fill in the gaps.

With an extensive academic portfolio and proven experience working within the US, Fathom’s flood data was incorporated into a floodplain quilt layer to provide a statewide rapid assessment flood inundation layer until BLE (base level engineering) can be completed. To facilitate this activity a Texas-based engineering firm, Aqua Strategies (www.aquastrategies.com) was enlisted and worked closely with Fathom and the TWDB to ensure that the data met the stringent standards of the Regional Flood Planning Groups who will ultimately benefit from the project.

To meet the project needs, Fathom compiled a ~10ft Digital Elevation Model (DEM) of the entire state, built using over 300,000 individual laser altimeter datasets (LiDAR). A customized hydraulic model was then run over this DEM, with the hydraulics computed at ~100ft. 

These results were downscaled to ~10ft resolution, providing an output of flood depths for pluvial, fluvial, and coastal flooding at four different frequencies: 1 in 5 (20% chance in a given year), 1 in 10 (10%), 1 in 100 (1%), and 1 in 500 (0.2%).

A complete digital elevation map of Texas’ terrain was produced during the project.

The results The flood planning program resulted in a flood planning hub for flood data and resources. Data layers for critical infrastructure, flood infrastructure, flood risk, hydrology, jurisdictional boundaries, parks, population, property, terrain, and transportation were included as part of this flood risk resource.

Three depths for each flood frequency at a 10ft resolution were “mosaicked” together to enable the selection of the greatest flood depth where the different datasets overlap. 

Composed of state and federal flood risk data, TWDB effectively reached their goal of achieving a consistent flood risk layer for the entire state of Texas, USA at a 10ft resolution with their floodplain quilt.

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I’d like to thank the effort of regional flood planning groups, its members, technical consultants, the public and other agencies who have been putting in a lot of time to put together regional flood plans, essentially going to come together as the first State Flood Plan for Texas.

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Aqua Strategies is proud to work with Fathom on this truly innovative method for greatly improving how we develop flood risk maps in Texas. Successful delivery on this project demonstrates possibilities for the remaining 49 states, and beyond.

How the Texas Water Development Board used Fathom data to provide statewide flood hazard coverage

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Fathom-US 2.0 Flood Hazard Data

A paradigm shift in our understanding of US flood risk.