Maintain and Increase the Capacity of Stormwater Infrastructure to Accommodate Variable Precipitation

Average annual precipitation has increased by roughly 5 percent across the U.S. since 1900, and much of this has come in the form of heavy downpours, especially over the last 50 years. River-flow increases have been observed in the U.S. Midwest and Northeast, and very heavy precipitation events are projected to continue to increase across the country, with the potential to cause infrastructure failures and loss of life. Low-impact systems for stormwater management, which allow for higher peak flows and increase water storage when drainage systems are overwhelmed, can reduce infrastructure failures and associated natural resource damage. These systems can also reduce negative impacts to water quality and benefit aquatic habitat when pulses of asphalt-warmed waters are held to infiltrate through bioretention features rather than directly entering streams and lakes. Several forms of low-impact stormwater infrastructure listed below have been found to be beneficial and effective and could be combined with forms of conventional stormwater infrastructure, such as roadside ditches or piping systems. This approach can be applied proactively in advance of precipitation events or reactively after damage or disturbance present opportunities to rebuild in a more climate-informed and resilient manner.

Projected changes in precipitation and temperature are expected to alter hydrologic regimes through changes in streamflow, snowpack, evapotranspiration, soil moisture, surface runoff, infiltration, flooding, and drought. Many of the roads, trails, campgrounds, and other infrastructures that support recreational activities were constructed in a manner that restricted stream-channel flow and reduced floodplain connectivity, among other hydrologic alterations, which today has produced an inability to adequately accommodate higher peak flows and flooding, especially during extreme precipitation events. Damage to roads, trails, campgrounds, and other infrastructure brings with it the potential of damage to natural resources, especially where impervious or below-grade surfaces concentrate water into flow pathways, generating high-velocity runoff and erosion of soils. This strategy describes options to prepare for uncharacteristic hydrologic events in order to reduce the extent or severity of damage to both recreational infrastructure and adjacent natural resources. It is important to keep in mind that modifications to maintain hydrology at one site may have negative impacts on hydrology at another site.