Realizing Resilient Watersheds
Land development projects add impermeable roads, structures, roofs, sidewalks and parking lots. Land development also reduces natural vegetation cover, including grasses, trees and brush. In addition, development alters or eliminates the existing natural water flows and drives increased surface runoff volume.
As land development projects progress and address the challenge of moving stormwater, it is time to consider what will be built and what will be preserved — not just to keep moving and using stormwater on a site but also for the benefit of all downstream.
By adopting proactive design standards, weighing downstream risk and embracing stormwater management early, land development projects can create success for all.
Develop Design Standards
Stormwater design standards consider the intensity-duration-frequency (IDF) of a hypothetical rainfall event. This hypothetical rainfall event has only one peak — like a bell curve — and lasts a defined timeframe, such as 24 hours. Unfortunately, the commonly used IDF standards and existing hydrologic criteria are based on data from the 1960s and focus on severe weather events rather than the changing weather patterns, such as back-to-back rain events that can greatly increase runoff volume. Today, we have historical rainfall data to show how rainstorms happen, including peak intensity and typical durations.
Design standards often provide guidance that is too simplistic for land development projects, focusing only on rerouting runoff and not incorporating all the impacts of weather events.
Assess Downstream Risk
Current design and planning guidance passes the risk of water runoff and flooding downstream. As the land is changed and the existing hyperefficient natural water flow paths are disrupted, land development projects must take responsibility for the runoff generated by their site to avoid passing on costly problems to surrounding communities. Projects must look beyond simply meeting regulations and provide practical steps for incorporating runoff.
An increase in water flow presents a significant increase in energy and strength. An inaccurate design of runoff mitigation can push flooding downstream, tear up river banks, widen waterways, undermine road crossings, degrade existing stormwater infrastructure and more.
Understanding and appreciating the natural flow paths and land cover at the project site and beyond is essential to the best long-term stormwater development strategy. Respecting naturally established watersheds and water runoff patterns is an important part of taking a holistic approach toward creating an optimum plan while mitigating unnecessary risk. There are opportunities within the design development phase to integrate stormwater management strategies throughout the land parcel — look for options to infiltrate water, reduce impervious surfaces, integrate diverse vegetation, and retain and reuse water.
Engage Early Collaboration
There is value in understanding, accommodating and leveraging the way water naturally flowed on a piece of land for centuries. Expanding the land development team to include stormwater management from the start helps create the most effective design plans.
Stormwater should no longer be considered waste that must be removed but a resource that can be incorporated into land development. In addition to focusing on pollutant reduction from runoff mitigation, stormwater management brings a range of tools and solutions that can enhance a development project by using rainfall where it falls.
Smarter stormwater designs explored and incorporated early in a land project can introduce flexible solutions that meet regulations and provide benefits to the landowner and community. Collaboration among planners, engineers, architects, landscape professionals and scientists can identify and present a range of options that meet the intent of the regulations while building infrastructure that has multiple uses for the community.
