Floods are costly and dangerous events that impact communities across the U.S. every year. The National Oceanic and Atmospheric Administration predicted above-normal activity for the 2020 Atlantic hurricane season, running from June 1 through November 30. The month of August saw the unusual event of two weather systems coinciding in the Gulf of Mexico, with Marco weakening into a tropical depression just before making landfall in Louisiana and Laura slamming into the Louisiana-Texas border area as a category 4 hurricane. In addition to high winds, such events bring storm surge concerns and rising waters can quickly overcome citizens. Any advance notice of flood risks and the ability for emergency management agencies to appropriately plan is vital to saving lives and protecting property.
The Department of Homeland Security (DHS) Science and Technology Directorate (S&T) released “Low Cost Flood Sensors: Urban Installation Guidebook” to do just that—help communities deploy and operate low-cost sensors for flood monitoring and management. The guidebook captures the process and results of a recent 18-month operational test of S&T’s low-cost sensors (LCS) in Mecklenburg County, North Carolina, from the initial steps of selecting sensor locations and installation to operation and maintenance. Best practices are now available for other regions across the country to learn from while implementing their own sensor infrastructure.
“S&T partnered with Charlotte-Mecklenburg Storm Water Services (SWS) for the leadership in flood risk management and technology innovation,” said Dr. David J. Alexander, DHS senior science advisor. “The Flood Apex program was looking for partners interested in driving research to action. Charlotte stepped up to the plate offering a unique opportunity to evaluate and demonstrate new risk methods and technologies in a living laboratory that experiences inland and urban flash flooding and occasional hurricane-related flood events within a large and growing metro area. The community guidebook is a key outcome of the project. S&T is optimistic that the guidebook will find a wide audience since it was developed by a local and nationally-recognized community leader in storm water services and flood risk, is in line with current FEMA and commercial insurance trends, and can take advantage of emerging technologies, such as the new low-cost flood sensors and other risk tools from the project.”
Mecklenburg County is the state’s most populated county and one of the fastest growing metropolitan areas in the country. The Charlotte-Mecklenburg SWS is a joint municipal/county storm water utility that covers the city of Charlotte and surrounding towns, and works to provide year-round management of rainfall runoff, reduce flooding, restore floodplains and protect the water quality of surface waters county-wide.
The operational testing was the culmination of a three-year partnership between S&T’s Flood Apex Program and Charlotte-Mecklenburg SWS to install and test LCS and improve local flood risk tools. Sensors were placed in varying types of locations (e.g., flood-prone roads, bridges, waste water life stations, dams) throughout the area to collect data from different potential flooding situations. Charlotte-Mecklenburg SWS also sought to study the benefits of the LCS supplementing an existing, robust streamflow and rainfall gauge network via another partnership with another agency: the U.S. Geological Survey. S&T’s sensors were successfully installed in every location and setting chosen, and the project discovered that the mounting hardware and setup could be adapted to any setting. The LCS operated as they were intended and successfully met or exceeded the accuracy requirements for each use case.
A second guidebook was developed from the Charlotte-Mecklenburg SWS and DHS S&T partnership, the “Flood Risk Assessment and Reduction Community Guidebook,” as a reference for communities working towards mitigating flood-related hazards by monitoring water levels. The document builds on the lessons learned from the North Carolina sensor tests and presents recommendations that are scalable to other communities of varying sizes, geographies and available resources as they manage their own flood risks.
“The partnership between Charlotte-Mecklenburg SWS and DHS S&T has been very productive—at both the local and national levels,” shared Dave Canaan with Charlotte-Mecklenburg SWS. “SWS’s extensive knowledge on collecting data in the field was leveraged with the deployment and testing of the sensors. And SWS’s expertise in managing a local, floodplain buyout for the last 20 years proved to be instrumental in creating the “Flood Risk Assessment and Reduction Community Guidebook.” These advances that should lead to reduced flood losses would not have been possible without S&T’s vision, resources and professionalism.”
In total, S&T and Charlotte-Mecklenburg SWS deployed 118 flood sensors across the region. The guidebook describes the experiences of LCS placement and physical installation; covers pre-deployment activities (e.g., functional assessments and preliminary site evaluations); highlights the LCS testing process through field deployment, installation needs, frameworks, and deployment planning; details ongoing evaluation and modification to achieve optimal performance; and serves as a reference for daily operation and maintenance of the LCS network.
Recommendations include identifying the desired locations of LCS based upon local flood risk and selecting vendors who can provide supporting products that meet the unique communication requirements for the particular local area. For instance, depending on the location, the LCS may require one or a combination of radio, cellular or satellite communication capabilities.
Additionally, the guidebook provides recommendations on handling data storage, accessibility and viewing. Some communities may have existing software that can integrate with the LCS system, while others will need to determine how the LCS and accompanying software will meet their community’s needs best. Included factors to consider when deciding to use either pre-existing or newly-purchased software include: vendor’s ability to provide data hosting and visualization, alerts and notifications, system redundancy, security, and cost.
Another helpful feature for communities concerned with flood mitigation techniques are the descriptions of the various use cases, which detail the LCS testing process, placement selection and overall effectiveness. The appendix of the guidebook provides the Charlotte-Mecklenburg SWS forms and checklists that serve as an example and can be modified for use by other communities.
According to Jeff Booth, director of S&T’s Sensors and Platforms Technology Center, “Our collaboration with Charlotte-Mecklenburg allowed us to modify the sensors and provide additional functionality specifically needed by local communities. Their knowledge, experience and recommendations on installation, monitoring, operations and maintenance will help other communities with their investments of a low-cost sensor network for flood hazard mitigation.”
S&T’s collaboration with Charlotte-Mecklenburg SWS runs through spring 2021. Together, the goal is now to work towards developing real-time flood inundation mapping, tracking losses avoided, and prioritizing future flood mitigation (cost and technique). Current research efforts are focused on sensor communication—whether the sensors can connect to existing emergency management systems, if they can send direct notices to mobile devices, and if they can interact with other outreach vehicles like social media platforms.
The promising ongoing LCS work and supporting guidebooks demonstrate S&T’s commitment to preparing localities to handle flood events and making tools and data easily accessible to flood-prone areas. The S&T and Charlotte-Mecklenburg SWS flood-focused partnership has the potential to serve as a nationwide model, significantly improving the ways that communities plan for floods, keeping communities and citizens safer, and making them more resilient.