Southeastern Virginia Continues to Break New Ground on Climate Change Policy

Snapshot: Southeastern Virginia regional governments are continuing to set the pace on climate change adaptation as they act to address a range of climate change impacts. Hampton Roads localities, which already set their own estimates of sea level rise (after years of state and federal government inaction) are now looking at ways to address both sea level rise and increased rainfall intensity, proposing adaptive stormwater and infrastructure design standards and expanding regulation into the 500-year floodplain.

Background: Virginia is setting the pace on climate change adaptation, making a number of breakthrough moves in legislation and transportation standards to address climate change impacts. In the southeastern Virginia region known as Hampton Roads, local governments established regional guidance on rates of sea level rise and are required to include sea level rise impacts in their long-range land use plans.

Now the region is considering another set of regional standards to address its flooding problems. Under review at the Hampton Roads Planning District Commission (HRPDC) are proposals to set regional guidelines for:

·         increased rain intensity,

·         updated design standards for stormwater systems to handle more intense rainfall, and to address the combined impacts of sea level rise and changed rainfall intensity, duration, and frequency by developing new design standards,

·         moving to regulate in the 500-year floodplain,

·         including new combined probabilistic flooding estimates in long-range land use plans and floodplain management plans, and

·         requiring additional margins of safety when building in a floodplain (freeboard).

In taking these actions, the Hampton Roads region in Virginia would become one of the only areas in the country where localities are acting on their own to confront a range of climate change impacts with specific design guidelines. In the vacuum created by state and federal government inaction, these localities are taking matters into their own hands to protect their residents.

The Hampton Roads Planning District Commission is studying:

o   Whether to change local standards to address more intense observed rainfall events, which are estimated to be 20% above the 24-hour duration rainfall conditions currently contained in NOAA Atlas 14. HRPDC has regional sea level rise estimates and this would be the next step to deal with flooding and determine runoff standards for stormwater systems. The City of Virginia Beach is changing its stormwater regulations in the face of new rainfall data.

o   How to incorporate sea level rise and non-linearity into the design of stormwater tailwater elevations. We see older stormwater outfalls going underwater with rising sea levels, rendering them useless during high tide events. To prevent that in the future, we need to redesign stormwater systems to fit the new reality.

o   Combining the effects of sea level rise and increased rainfall in stormwater models. These approaches use multiple joint probability design storms that look at new precipitation estimates and tailwater conditions. Current storms with more intense rainfall and with compromised outfalls mean these storms are overpowering existing systems. This analysis will help identify areas seeing impacts now and will increase in the future.

o   The need to regulate the 500-year floodplain (.2% annual chance of being flooded) as well as today’s 100-year floodplain (1% annual chance of being flooded). With increased rainfall events and sea level rise, we are seeing flooding outside of the currently regulated 100-year floodplain. Regulating in a larger area comprising the 500-year floodplain would add an additional margin of safety and protect structures in those areas into the future.

o   How to include these new flooding estimates into long range comprehensive land use plans and floodplain ordinances. Current plans and ordinances are using outdated assumptions about flooding and do not account for combined sea level rise/rainfall intensity impacts, as well as adding margins of safety for future conditions.

o   Whether localities should adopt a minimum 2 feet of freeboard in floodplains (Freeboard is an additional amount of elevation on a structure to put it higher than the floodplain). Currently the minimum freeboard required by the Federal Emergency Management Agency is 1 foot above the 100-year floodplain. The HRPDC is also studying whether to require 3 feet of freeboard for critical structures and how to develop appropriate freeboard standards for structures based on the location, useful life, and criticality.

All of this is really down in the weeds but is essential to making our communities more resilient in the face of the increased flooding we are seeing…and will see. These initiatives constitute a major step forward in local/regional resilience policy and should be considered in every US coastal community. These steps will also help other Virginia localities as they attempt to deal with these resilience challenges.