Virginia has been subject to recurrent flooding in recent years, especially in its coastal areas. Chapter 978 of the 2020 Acts of Assembly, introduced as HB 1217, directed the Virginia Department of Transportation (VDOT), in collaboration with the Commonwealth Center for Recurrent Flooding Resiliency (CCRFR), to identify public transportation infrastructure under the jurisdiction of VDOT in Planning District 8 (PD8) that is at risk of deterioration due to recurrent flooding.(*2) VDOT was directed to (i) identify the issues related to recurrent flooding and the scope of such issues and (ii) make policy and budget recommendations to alleviate such issues (Study).

In response to HB 1217, VDOT, through the Virginia Transportation Research Council (VTRC), has and is continuing to collaborate with CCRFR consortium member, Virginia Institute of Marine Science (VIMS), and other stakeholders on studies in coastal areas, including PD8. Through this collaboration, the following efforts have been performed and are currently being performed to advance this Study:

a) Overlay of VDOT-maintained roads with the Federal Emergency Management Agency’s (FEMA’s) flood hazard zones to approximate roadway segments and bridges that are potentially more susceptible to flooding;

b) Assessment of historical road closure frequency and duration due to weather-related flooding incidents from 2008–2019;

c) Evaluation of land cover and other landscape changes and potential relation to flooding; and

d) Analysis of road networks as it relates to recurrent flood frequencies to assess roadways and transportation pathways and the impact of road flooding on access to and from critical and sensitive transportation infrastructure.

As to the identification of at risk public infrastructure, the FEMA overlay analysis indicates that, out of the total 6,638 miles of VDOT-maintained highway network assessed in PD8, 97.3 percent of the network (6,459.4 miles) is within a minimal flood hazard zone; two percent of the network (135.9 miles) is within the most vulnerable flood hazard zone, with a 1% annual chance of flooding; 0.4 percent (24.1 miles) of the network is within the flood hazard zone with a 0.2% annual chance of flooding; and 0.3 percent of the network (18.4 miles) is within an area of undetermined flood hazard zone.

Assessment of the historical (2008-2019) road closure data based on VDOT’s 511 operations database further shows that there were a total of 2,912 high water-related road closures, with 2,259 of the incidents resulting from hurricane/flood reports and 653 of the incidents resulting from standing/ponding events. Of the total high water-related road closures, 78 (66 hurricane/flood events and 12 standing/ponding reports) locations reported having experienced high water-related closures more than four times in the twelve-year period between 2008 and 2019. For those locations having more than four high water-related road closures during that time, an average closure time of 88 hours for hurricane/flooding incidents and 102 hours for standing/ponding incidents was reported. As described later in this report, there are limitations associated with 511 data that are atrributable to the variety of data sources and circumstances of collection.

Taken with the results of other statewide and regional initiatives and studies that were reviewed as part of this effort, and the discussion with VDOT’s Northern Virginia (NOVA) District personnel regarding their firsthand experiences and observations, this Study reaches a number of findings regarding factors related to an increase in recurrent flooding. These factors include:

i) Changes in historical rainfall pattern intensities, duration, and frequencies over several decades has resulted in increased inundation;

ii) Antiquated or limited standards and rainfall records used as the basis for infrastructure selection during the early to mid-20th century resulted in legacy drainage infrastructure that no longer has the capacity to meet the emerging design storm needs of today;

iii) Infill development and higher land use densities resulting from rezoning or existing land use entitlements, as well as drainage pathway modifications, has contributed to drainage-related problems including flooding;

iv) Drainage interconnections to localities and other entities with either old or legacy infrastructure or differing design criteria has caused challenges in designing and providing for adequately sized drainage infrastructure; and

v) Funding availability and mechanisms, and corresponding dedicated administration resources, to repair and/or upgrade existing infrastructure is very limited and has resulted in a diminished ability to appropriately address many, if not all, of the causes of recurrent flooding infrastructure.

The compounding effects of these factors have been identified in this Study as the causes and issues that may lead to the experienced recurrent flooding in PD8.

VDOT recognizes that the causes of recurrent flooding in PD8 are partially due to historical causes, issues related to development over time at the local level, as well as the broader issue of climate change influence that is currently being evaluated by the Commonwealth, statewide and among various state agencies and stakeholders. Through VDOT’s active involvement in this and other studies related to climate change and resiliency, VDOT offers the following recommendations:

1. Support Key Statewide & Regional Studies: Continue to support the update of the authoritative National Oceanic and Atmospheric Administration’s (NOAA) Atlas 14 rainfall records, which are presently current through approximately 2004, to include more recent historical records for the region. At the same time, continue active development, participation, and funding of key regional and statewide studies, such as the statewide expansion of the precipitation study, to estimate future projected rainfall patterns that incorporate climate change influences. Identify data gaps and initiate applied research to provide information that can be used directly by engineers and designers, such as future projected streamflow estimates for very large drainage systems, and adaptive design standards that can be utilized in future at-risk projects.

2. Participation and Coordination with Major Commonwealth Efforts: Actively participate and align efforts and policies with statewide efforts including the Virginia Coastal Resilience Master Planning Framework and the Virginia Coastal Resilience Master Plan, and findings from the recently concluded study arising from the Joint Commission on Science and Technology (JCOTS), The Impact of Climate Change on Virginia’s Coastal Areas, among others.

3. Continual Improvement and Coordination of Datasets and Tools: Collaborate with other entities to continually improve, update, and expand existing datasets and tools, or create new ones where needed, related to recurrent flooding to better inform and understand causes and issues related to existing infrastructure as well as aiding in the identification of future potential at-risk infrastructure, both for existing and new, and the evaluation of potential solutions.

4. Continual Assessment of Transportation Network: Continue to conduct further assessments with other partners to evaluate the implications and effects of recurrent flooding, climate change, and resiliency with a focus on transportation infrastructure and to evaluate options that will enhance VDOT’s ability to mitigate, prepare and respond to these issues.

5. Enhanced Collaboration and Partnership between State and Localities: Continue and enhance collaboration and partnership between state and localities in identifying infrastructure subject to recurrent flooding, evaluating potential causes, and aid in identifying and implementing solutions to alleviate the problem.

6. Funding of Flood-Related Projects: It is currently premature to make specific funding recommendations, but it is clear that funding will need to be identified for several key activities necessary in the development of a program and strategies to address recurrent flooding and resiliency for transportation infrastructure. Those activities include but are not necessarily limited to: (i) studies; (ii) infrastructure improvement; (iii) tools and technology for flood prone areas; and (iv) capacity building. Sources of funding for these activities will need to be identified for state and local projects and could include both federal and state funds.
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(*2) Public transportation infrastructure includes roads and bridges under the jurisdiction of VDOT. PD8 includes Arlington County, Fairfax County, Loudoun County, Prince William County, City of Alexandria, City of Fairfax, City of Fall Church, City of Manassas, and City of Manassas Park.