Original photo credit: The New York Times

What do we know about floods?

A flood might occur after heavy rainfall due to extreme weather events or the rising sea level because of climate change. There are multiple factors into why excess water cannot be discharged in a short period. Many flooded areas cannot carry extra water. But lacking of sufficient porous surfaces, especially in the urban area, is the primary reason.

Why Does green infrastructure matter?

A green infrastructure is a sustainable approach to managing stormwater runoff and reducing the risk of wet weather impacts such as hurricanes.

Unlike the traditional grey stormwater infrastructure that uses piped drainage system to treat extra runoff water, the green infrastructure is designed to move urban stormwater away from the built environment with cost-effective, aesthetical-pleasing, and low-maintenance solutions.

Here are a few typical green infrastructures that you might see in your neighborhood but are unaware of.

Rain Garden
Bioretention pond (or Bioswale)
Vegetative swale
Infiltration trenches
Green roofs
Downspout disconnection
Rain barrel Cisterns
Permeable pavement

More sustainable credits:

[SITES]. Water 3.1: Manage precipitation on site

Retain the precipitation volume from the 60th percentile precipitation event as defined by the U.S EPA.

Retain precipitation volume through on-site infiltration, evapotranspiration, and reuse, such as implement runoff-reduction strategies or cisterns, etc.

Ensure the section of the site maintenance plan is completed and includes the maintenance activities used to ensure the long-term effectiveness of stormwater features.

[SITES]. Water 3.3: Manage precipitation beyond the baseline

Through on-site infiltration, evapotranspiration, and harvest use, retain or treat the maximum precipitation volume possible beyond the required baseline precipitation volume to 80th, 90th, or 95th percentile precipitation event.

[LEED ND]. GIB: Rainwater Management

To best replicate natural site hydrology processes, manage on-site the runoff from the developed site for the percentile of a regional or local rainfall event, using low-impact development (LID) and green infrastructure. The measurement is done by the rainfall event, such as 80th, 85th, 90th, 95th percentile rainfall event.

Both strategies listed above use daily rainfall data and the methodology in the U.S. Environmental Protection Agency Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal projects under Section 438 of the Energy Independence and Security Act to determine the percentile amounts.

By the way…

The FEMA flood map is the place to check if your location might be exposed to flood hazards. This database maintains flood maps and demarcates zones used by the national flood insurance program. It contains both 100-year flood zones and 500-year flood zones.
For better preparation for future flood events, check RiskFactor.com. The online database allows users to calculate the potential risk, for example, a yearly financial impact on property owners.
Often, the sea surface temperature that develops across the east-central equatorial Pacific will also impact local precipitation. They are known as the ENSO cycle. A quicker way to understand La Niña and the difference of El Niño and La Niña at YouTube.
Link to U.S. Environmental Protection Agency to learn about Green Infrastructure.
Based on the climate data in 2019, the 60th percentile precipitation in the Washington DC area is 3.80 (inch); the 95th percentile precipitation is 6.56 (inch).
Background music: Mozart/ “Queen of the Night aria” from the opera “The Magic Flute” (Die Zauberflöte)