Maryland Flood Mapping Website

Challenge

A Maryland state law issued in 1933 required permits for activities that cause physical changes in the course, current, or cross-section of any (riverine) waters of the state. After the National Flood Insurance Program (NFIP) was implemented, the federal process of modifying Flood Insurance Rate Maps (FIRMs) did not match well with the Maryland permitting process.

Solution

When Maryland became a Cooperating Technical Partner (CTP) with the Federal Emergency Management Agency (FEMA) in the early 2000s, state officials worked with the federal government to update digital Flood Insurance Rate Maps in a way that aligned with the Maryland stream permitting process. This project also provided an opportunity for the state to collect updated data on bridges and culverts in the floodplain.

Using a combination of statewide Light Detection and Ranging (LiDAR) topographic data and state-generated stream flow data, Maryland initiated a flood map revision process through the CTP program. This process involved developing flood study engineering models that incorporated updated data for almost all road crossings in the state.

Benefit

Flood elevations have been established or are being prepared for almost all rivers and streams in the state. These models include information on bridges and culverts on the streams that were studied, cross-section information and flow characteristics. Maryland plans to incorporate a cross-section viewer this year.

The flood study engineering models are available on a publicly accessible website. The data includes current FEMA engineering models Hydrologic Engineering Center-River Analysis System (HEC-RES), stream flows and cross sections, and photographs of bridges and culverts associated with the waters in Maryland. The models and supporting information have all been georeferenced and are shown on the website in their actual mapped locations. With this information, staff can respond to engineering data requests and FEMA Letter of Map Amendment (LOMA) processing in less time and at less cost.

The state is currently working to incorporate submitted data, updates, and information into day-to-day permitting operations. An email exchange system communicates to local NFIP officials that a state permit application for changes in a floodplain in their community has been received.

Lessons Learned

Risk MAP Phases

  • Discovery
  • Data Development and Sharing
  • Risk Awareness and Mitigation Outreach
  • Proposed NFIP Map Changes and Impacts
  • Preliminary Map Release and Mitigation
  • Due Process and Path Forward

Risk MAP Goals Advanced

  • Increased Deployment
  • New, Validated, and Updated Engineering Initiated or Achieved
  • Advancing Action
  • Increasing Awareness

One noteworthy benefit of providing open access to flood study data is that the data are available to other agencies. For example, the Annapolis office of the U.S. Fish and Wildlife Service is now using these data in the design and planning for stream restoration projects. The engineering models used in the design of wetlands and riparian vegetation stream restoration projects can be downloaded. The Fish and Wildlife Service is in the process of providing the more detailed stream field survey data developed for these projects to Maryland so that the engineering models can be enhanced and updated.

Open access to the engineering models enables a robust process for improving the accuracy of the engineering models associated with the flood hazard mapping in Maryland. The Fish and Wildlife Service is also proposing to use the Maryland data as part of the Environmental Protection Agency’s Watershed Resource Registry to predict stream stability through Geographic Information Systems (GIS). These predictions can be used to identify and prioritize locations for stream restoration and protection projects.

Resources

Website: Maryland Flood Risk Maps

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Last updated April 28, 2021