Practices for Integrated Flood Prediction and Response Systems (2021)

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1   A critical issue facing departments of transportation (DOTs) across the United States is predicting and responding to flooding events. Roadway and bridge flooding has significant economic impacts. State DOTs and other state and local agencies have implemented inte- grated flood warning and response systems to mitigate the effects of floods. This practice is critical for staging personnel, deciding when to close roads, inspecting bridges, tracking floods throughout the state, and planning recovery. Support for these efforts often integrates items such as internal products, flood inundation mapping using current and projected conditions, turnkey products on the market, the United States Geological Survey (USGS) gaging network, and the National Weather Service (NWS) flood forecast system. In addition to predicting flood inundation, state DOTs are tasked with alerting the public about affected areas and protecting them from these hazards. DOTs and other agencies must determine the flood’s extent and severity to effectively work with emergency management and inform the public about road closures and detour routes. The multiple methods of warning the public about floods vary by scale, including (a) warnings on official websites, (b) warning lights tied to stream gages, (c) sensors, (d) personnel blocking off areas, and (e) leveraging of federal resources, such as USGS and NWS products. This synthesis documents an overview of the state of the practice from agencies involved in finding new or innovative ways to improve flood management and response systems. It iden- tifies state DOTs with a track record of successfully implementing strategies and practices in managing critical flooding cases. Information gathered includes, but is not limited to, (a) flood prediction methods, (b) risk thresholds that trigger action, (c) methods and instruments used by DOTs to monitor flooding, (d) methods DOTs use to determine the extent and severity of floods, (e) available warning systems and methods, (f) DOT practices for alerting the public, (g) coordination with other agencies, (h) internal communication, (i) successful systems as reported by DOTs, (j) weaknesses in existing methods, and (k) problems that remain unsolved. Several reports and studies have been completed on the importance of integrated, accu- rate, and timely flood monitoring, prediction, warning, response, and impact assessment methods. There is a need to synthesize these efforts and garnish examples of successful state DOTs that are reported to be effective to assist other states in managing critical flood events. This study provides state DOTs and other transportation agencies with useful infor- mation on successful practices that address critical flooding events. The information for this synthesis was gathered through a comprehensive literature review, a survey of state DOTs, and subsequent interviews with seven states selected for further study. Forty-eight DOTs (47 states and the District of Columbia) responded to the survey, attaining a survey response rate of 94%. After reviewing documentation in the literature and the detailed survey responses, the states of Idaho, Iowa, New York, North Carolina, South Carolina, Texas, and Washington were selected and interviewed as case examples, using the criteria outlined S U M M A R Y Practices for Integrated Flood Prediction and Response Systems

2 Practices for Integrated Flood Prediction and Response Systems in Chapter 1. The following observations were made on the basis of the DOT survey data, detailed interviews, and literature review. • Various FHWA initiatives (e.g., Sustainability Resilience Pilot Program, Every Day Counts) paired with investments in national programs [the National Oceanic and Atmospheric Administration (NOAA) National Water Model and the USGS National Water Informa- tion System (NWIS)] reflect the importance of effective and accurate flood modeling and management systems. • Advancements and integration of relational database systems, real-time data collection tool technologies [e.g., LiDAR (light detection and ranging), gages], flood prediction models, data processing and visualization software [e.g., geographic information system (GIS)], and data-sharing platforms (e.g., USGS’s NWIS, NWS’s River Forecast Center) have made substantial contributions to the effective management of floods. • The survey indicated that slightly more than half of DOTs (25 out of 48) reported that they consider their integrated system for flood prediction and response as successful. Common plans or initiatives that have contributed to successful systems are the use of USGS gages, the importance of communication between agencies, and BridgeWatch, a proprietary software that provides real-time monitoring technologies for public officials and field personnel. • On the basis of the 43 DOTs responses, approximately half of state DOTs reported using USGS’s NWIS for flood monitoring, and a majority of the DOTs indicated that they use federal stream gages as an instrument and tool for flood monitoring. The other most common instruments and tools DOTs use for flood monitoring are federal rain gages, non-federal stream gages, and GIS. Most of the DOTs indicated visual inspection as the most common tool used in determining the extent of flooding severity. • The DOTs provided information on risk thresholds that trigger action. Common responses from DOTs indicated that NWS issues the warnings and parameters that DOTs apply to issue a flood warning. According to a self-ranking, the most important infor- mation used in states’ flood warning systems is observed stream stage, observed stream inundation, and bridge scour. • DOT survey results identified a hydrologic/hydraulic model as the most common type of flood prediction method used by DOTs. For the platform/model of the flood prediction model, most DOTs reported that the flood prediction model is produced by a federal agency [e.g., USGS, Federal Emergency Management Agency (FEMA), FHWA, NOAA, NWS, United States Army Corps of Engineers, Bureau of Reclamation]. • The survey showed that the most widely used communication tools and methods to alert the public in response to flooding events are radio, social media (e.g., Facebook, Twitter, Instagram), television, signs, and 511 systems. For communicating and working with other state agencies when responding to flood events, direct calls and emails, agency sharing (e.g., homeland security, police), and Emergency Operations Centers (EOCs) were identified practices and approaches applied by the DOTs. Email lists, conference calls, and an emergency management center were identified as being frequently applied in DOT internal communication systems that are structured to respond to flood events. • Many DOTs reported cooperation from local agencies in the state, adequate state resources (in staff and funding), and a continuous public awareness campaign regarding the emergency response and warning systems as key factors and attributes that have led to the success of flood response systems. The most common methods used to facilitate emergency response systems were identified: (a) frequent coordination meetings among the stakeholders, (b) involvement of the FHWA division offices or other FHWA assis- tance, and (c) a committee established to oversee and contribute to effective emergency response initiatives.

Summary 3   • Interviews with case example states demonstrated that the close relationship among the state DOT divisions (e.g., Hydraulics Design, Asset Management), as well as between the state DOT and other states and federal offices (e.g., FEMA, Department of Natural Resources), is a key factor in a successful flood prediction and response system. A close working rela- tionship with USGS’s gage program—particularly the rapid deployment gages, the fully functional stream gages designed to be deployed temporarily and quickly in emergency situations (USGS 2020b)—has proved helpful to several states. Furthermore, a coordinated and updated asset inventory document that is accessible to the key state DOT staffs is a method applied to keep the state DOT informed. • Interviews also indicated a need for investigating methods for further integration of developed BridgeWatch software into the state DOT’s real-time monitoring system while overcoming various issues associated with data format, type, resolution, and quality. Furthermore, an investigation is needed to determine an optimal warning-level setting for a range of scenarios to minimize false alarms because the degree of false alarms varies according to local hydrology and hydraulics. Though hydrology and hydraulic challenges differ depending on land cover and physio- graphic region, there is a need to improve real-time flood model predictions, especially for back- water hydraulic conditions and other hydrologically complex areas (e.g., snowmelt flooding or king tides). Furthermore, the need for advancements in data collection (e.g., bridge scour) was a key issue for most of the states interviewed. Understanding the required spatial-temporal resolution of data needed (e.g., issues with the stream network without the monitoring gages or low-frequency monitoring) and data continuity (e.g., for identifying hydrodynamics) is necessary for decision making. Research is also needed to facilitate data sharing and integra- tion (e.g., incorporating disparate data types) of research to address difficulties and challenges. There is also a need to share and incorporate heterogeneous data between agencies and states, as well as with stakeholders. Spatial-temporal databases are needed to better facilitate data sharing, modeling, and analysis of the flooding risks and impacts on the transportation infrastructure. Urbanization and land development result in more frequently observed intense runoff events. The highly dynamic nature of these areas makes flood prediction particularly challenging. To better mitigate the impacts of intense runoff events, research is needed to better predict the downstream impacts of urbanization and land development.