Floodplain Restoration: An Ecological Approach to Stormwater Management
Developers often ask us, “How can we maximize the use of our site’s developable area?” But there’s a second, equally important question that often goes unasked.
“How can we expand our site’s developable area.”
That’s right. The developable area of a site isn’t necessarily finite. In some cases, you can actually create more of it with a strategic approach to stormwater management. But doing so requires a shift in mindset:
You must first learn how to work with the floodplain, not against it.
Stormwater Management Plans that Start with Floodplain Restoration Can Pay Big Dividends
Stormwater management broadly refers to any system used to reduce stormwater runoff, prevent water contamination, and restore the natural ecologies of the environment. And it’s during the early stages of a project that developers must decide how to manage a site’s stormwater and the necessary infrastructure.
Typically, Best Management Practices (BMPs) of stormwater management target three main areas:
- Volume Control
- Rate Control
- Water quality
“While developers have a variety of options to address these concerns, stormwater management is often a project timeline wildcard,” said Len F. Bradley, Supervisor and Associate at RGS Associates. “Local, state, and federal requirements can be complex. And because you don’t always know what stormwater factors you’re dealing with until the project begins, it’s often a big factor in the timeline, budget, and scope of a project.”
Traditional surface stormwater facilities reduce a project’s developable area. And underground stormwater facilities often inflate project infrastructure costs.
“Add to those concerns an existing stream and a 100-year floodplain traversing your development’s parcel, and the project impacts can be severe,” Len explained.
In grappling with these concerns, floodplain restoration has emerged as a promising alternative. Not only does it address the need for water management and control, but it also reduces the direct impact of land development on the surrounding environment, an approach that is much more ecologically sound.
“Many engineers, land planners, and developers instinctively assume that the floodplain area within their project site is worthless from a development standpoint,” Len said. “However, an innovative ecological approach to stormwater management and regional water quality is quickly changing those perceptions.”
A Brief History of Floodplains
Floodplains are low-lying areas next to rivers or streams that hold and filter high levels of stormwater runoff, including floods. In pre-settlement America (i.e., 1600-1700s), floodplains functioned as natural stormwater management systems by acting as a “sponge” for runoff.
Vegetation filtered the stormwater, allowing time for subsurface migration and replenishment of groundwater aquifers. This slowed down the runoff, reducing erosion.
But in the centuries since, as land was rapidly developed for agriculture, that all-important floodplain vegetation was removed.
“We ended up with more erosion, which meant that more low-permeability sediment filled the floodplains,” explained Len. “This had detrimental effects on the overall watershed, including increased flooding, more water pollutants, and sweeping deterioration to the general ecosystem.”
Now, with floodplain restoration, we have a way to counteract the destruction of our natural stormwater filter system.
“Restoring a floodplain is essentially a ‘reset’; the ecological equivalent of doing a factory reset to your cell phone,” Len said. “The goal is to re-establish the original functions of the pre-settlement floodplain. This includes removing sediment, replacing vegetation, and re-establishing the gravel layer to create opportunities for subsurface water migration.”
Floodplain Restoration Isn’t Just Good for The Environment. It’s Good for the Bottom Line
From a developer’s standpoint, implementing floodplain restoration as the BMP for stormwater management can create huge financial benefits.
“Floodplains are typically viewed as ‘unusable’ portions of land,” Len said. “However, when restored, the land becomes highly valuable and serves a necessary function. In turn, space that was originally reserved for stormwater facilities can be used for other purposes.”
More usable land means greater long-term financial potential for a project and the incentives for developers to consider floodplain restoration are good business.
“One project in Lancaster County utilized a floodplain restoration to increase developable area on the project by approximately 180,000 SF,” Len noted. “The design, permitting, and construction cost of the FPR approach was approximately $1.5M. The economic benefit of that additional developable land, assuming a use-average of $15/SF, generated an additional $2.6M for the developer.”
According to Len, those numbers are very conservative.
“One item that is normally overlooked in these cost benefit scenarios is the comparison of what the true cost of traditional stormwater facilities would have been had FPR not been utilized,” Len explained. “That infrastructure for a project of this size would have likely cost between $500k and $1M. The true return on investment was likely closer to $2M-$2.5M.”
And this is not the only application of floodplain restoration for savvy developers. RGS is looking at previously developed projects and determining if floodplain restoration can be retrofitted into a site to increase its yield.
“We are actively looking at previously entitled and constructed projects to determine if floodplain restoration can be implemented to remove existing stormwater facilities and increase developable land,” Len said. “A bigger win for the developer since main construction infrastructure is already in place and land is already owned. Any traditional yield goes directly to the developer’s bottom line.”
Floodplain restoration also provides all the benefits of stormwater management without the use of taxpayer monies. A federal mandate titled the Municipal Separate Storm Sewer System (MS4) permit requires municipalities of certain populations to reach specific pollution reduction levels for their watershed. This often necessitates extensive and expensive projects to meet such requirements.
“Floodplain restoration, when applied correctly, can achieve the goals set forth by municipalities without the use of taxpayer monies,” Len said.
An example of this is a 98-acre development from 2017 in Lancaster County, Pennsylvania. The development, which includes retail, commercial, warehouse, and medical offices, restored the surrounding 11.5 acres of floodplain.
“Beyond the inherent habitat and thermal improvements, the project removed 38,500 tons of legacy sediment, created 8.5 acres of additional wetlands, and provided pollutant reductions of approximately 5,773 pounds per year of nitrogen, 254 pounds per year of phosphorous, and 400 tons per year of sediment,” Len said.
All of this was done without the use of taxpayer funding.
The Transition to Floodplain Restoration
While there are clear benefits to implementing floodplain restoration, the transition from traditional stormwater BMPs is not seamless.
“It takes a great deal of education to convince the general public, regulators, and developers to make this shift,” Len said. “As conversations around floodplain restoration as a BMP become more commonplace, there will likely be more advocates for it during the planning, approval and permitting phase of projects.”
Another factor is that floodplain restoration is not appropriate for every project.
“Extensive watershed level and field assessments are needed to assure that restoration would be feasible,” Len said. “Development and zoning potential for the area surrounding the floodplain also needs to be reevaluated. Typically, lower density zoning is recommended for adjacent land; however, this may need to be augmented to incentivize developers to fund floodplain restoration projects.”
An Opportunity for Development and Ecological Benefits
Floodplain restoration projects are complex and require specific expertise to execute. But, when conducted by skilled stormwater management professionals, the ecological and financial benefits are significant.
“Being an environmental steward and a client advocate are not competing interests, but rather an opportunity for licensed professionals to develop creative stormwater approaches like floodplain restoration,” Len said.
With our decades of extensive stormwater management and floodplain restoration experience, RGS is here to guide you through the process. When you’re ready to discuss your next development project, contact the RGS team. We’re here to help you increase your ecological impact while lowering your financial burden on sites throughout Central and Southeastern Pennsylvania.”