Is a Riparian Forest Buffer Right for Your Site Development Project?

By Christopher Dellinger, P.E.

Riparian forest buffers are highly touted by regulatory agencies as the best way to manage stormwater on a developed site. They are environmentally friendly, sustainable, and a close approximation of the way runoff is managed by nature. In some cases, these buffers can be used to maximize the buildable space on a property, and long-term maintenance is minimal once plants are fully established.

What is a riparian forest buffer?

In the simplest terms, a riparian forest buffer is a wooded area along a stream. The plants and trees in a buffer absorb stormwater and filter pollutants before the runoff enters the watershed. These buffers are one of many stormwater Best Management Practices (BMPs) that site owners can use to meet regulatory requirements.

To receive credit for the BMP, a site owner must plant a buffer in an area that is not already wooded – where existing canopy cover is less than 30 percent. The width of the buffer can vary, but typically regulatory agencies require a minimum width of 100 feet.

However, riparian forest buffers are not suitable for every property. Let’s consider some of the pros and cons.

What are the advantages of riparian forest buffers?

The Pennsylvania Department of Environmental Protection (DEP) strongly favors their use.

Riparian forest buffers are vital to DEP’s strategy for meeting Chesapeake Bay pollutant reduction requirements. Nutrient and sediment pollution originating in New York and Pennsylvania has floated downstream to our nation’s largest estuary, killing local marine life and threatening fishing and tourism industries. As a result, the Bay states have agreed to reduce pollution in the watershed. Pennsylvania has committed to a goal of 95,000 acres of new riparian forest buffers statewide by 2025 as part of its pollution reduction approach. DEP will, no doubt, need support from the private sector to meet this goal. They are likely to look favorably on development projects that include the construction of buffers for stormwater management.

Riparian forest buffers are an environmentally friendly, sustainable approach to stormwater management that mimics Mother Nature.

The goal of stormwater management is to reduce flood risk and prevent pollution in our lakes, rivers, and streams. While structural BMPs like detention basins can address flood risk, they are not as effective as plants and trees at filtering pollutants. Additionally, they are resource intensive to manufacture and build, and their construction can destroy natural habitats.

As land development spreads to new areas, it is increasingly difficult for wildlife to find suitable food and shelter. Riparian forest buffers provide places for small species to live, and they produce edible fruits and nuts for these species to eat. The buffers are particularly advantageous to pollinator species, whose recent decline is a major threat to the agriculture industry and our own food supply.

The forest debris and shade help macro-invertebrate species in the watershed thrive, and this keeps fish populations healthy. A healthy stream can then process pollution more effectively. A Stroud Water Research Center study showed that buffered streams could remove 200 to 800% more nitrogen from runoff than unforested streams.

Forest buffers:

• Improve water quality (and reduce the cost of water treatment)
• Promote groundwater recharge
• Provide valuable habitat for wildlife
• Improve the health of fish populations

Riparian forest buffers can help maximize the buildable space on a site.

Stormwater management facilities are required for any land development project, and they are an important tool for reducing flood risk and protecting our water supply. However, detention basins take up space that could be used for a larger building footprint or site amenities. Buffers take up space, too, but they often use space that developers could not have built on anyway.

Developers are often restricted from building within 50 feet of a stream, and they typically are not allowed to disturb any wetlands that may be located along the stream. If the development is located within a high quality or protected watershed, developers will not be able to build anything within 150 feet of the stream, but they are able to plant a buffer there. This buffer can then be used to meet infiltration requirements, and the developer will not have to build an infiltration basin somewhere else on the site. Instead, they can use that land for more square footage or site amenities that will increase property value.

While structural BMPs require annual maintenance forever, riparian buffers require no maintenance once they reach maturity.

Structural BMPs like infiltration basins should be inspected once or twice a year. Maintenance includes cleaning out debris, fixing erosion, and replacing riprap as needed to ensure continued functionality. Site owners typically must commit to an operation and maintenance agreement as part of their land development plan approval. If they don’t comply with this plan, municipalities can enforce the agreements through legal means.

But even a properly maintained infiltration basin may malfunction, and the stormwater will not infiltrate as it should. When this happens, site owners must invest in repairs or replacement infrastructure to remain compliant with their permits. This can be expensive, and it can also be disruptive to anyone who uses the facility.

Riparian buffers don’t have that risk, and, once they mature, they require no maintenance at all. The key word here, however, is “mature.” For riparian buffers, maintenance can be both a pro and a con.

What are the potential pitfalls of riparian forest buffers?

Maintenance can be more intense for riparian forest buffers in the first five years than it is for structural BMPs.

Until a buffer achieves 60% canopy cover, weeds can thrive in the area, so frequent mowing and weeding will be needed. In addition, young plants and trees are particularly susceptible to invasive species that could weaken or even kill them before they can fully take root. Therefore, maintenance staff will have to check for signs of these species and remove them. Otherwise, the trees might die, and the site owner will incur additional expense replacing them.

Regional approval agencies don’t have a lot of experience with riparian forest buffers, so approvals could take more time.

While the main office of DEP is heavily promoting riparian forest buffers, regional district staff may not have seen them in local plans, and they may not have an established procedure for reviewing them. The same is true for county conservation districts. Education may be needed, so it’s important to work with a consultant that can prepare reviewing staff ahead of time.

Are riparian forest buffers right for your site development project?

Here are some questions to consider:

Do you have a stream on your property that is currently unforested?

The land along a stream must have less than 30% existing canopy cover to qualify for stormwater management credit from a riparian forest buffer.

Is the area around the stream subject to building restrictions?

Are there wetlands that would be disturbed by construction? Is the stream in a high-quality watershed? If so, you likely cannot build anything on the land closest to the stream. Planting a buffer there can convert it into usable space that helps you meet your stormwater infiltration and water quality requirements.

Do you have poor soil that can’t infiltrate water?

If your property contains clay soil or is located in an area where the groundwater is high, you will have a hard time meeting the infiltration requirements of your stormwater permitting. This is also true if there is Karst geology or limestone on site. In these cases, a riparian forest buffer will likely be more effective at infiltrating stormwater than an infiltration basin.

Are you prepared to commit the time and resources necessary for proper design and maintenance?

Trees can take approximately five years for initial establishment, but 60% canopy cover may not occur until 10-15 years after planting. Until that canopy cover is reached, you will have to do regular maintenance to ensure the health and continued growth of your buffer.

Maintenance tasks will vary based on the age of the buffer, the time of year, and the types of plants you select, but they typically involve mowing, weeding, spraying, replanting, and removing invasive species.

Proper design can lower the maintenance burden later on, so it’s important to work with a skilled consultant. Plants have varying tolerance for water, and there is a science to what you plant and where you plant it. An experienced and knowledgeable consultant can help you select plants that are most likely to thrive and require the least maintenance. They will consider site limitations like sunlight, soil, and weather conditions, as well as species characteristics like moisture tolerance, height, and resource needs. The resulting design will be functional, aesthetically pleasing, and practical to maintain.

Riparian forest buffers are one of the most effective ways to promote stormwater infiltration and prevent pollutants from entering our water supply from rain and runoff. They promote healthy habitats for wildlife and fish populations, and they are self-sustaining once fully established. For these reasons, they are highly regarded by regulatory agencies like DEP. They are particularly beneficial to site owners if a property has poor quality soil or is located in a high-quality watershed, helping them to maximize the buildable space on a parcel. However, local regulatory officials may be unfamiliar with them, and initial maintenance requirements can be more intense during the first 5-10 years than they are for structural BMPs like infiltration basins. Site owners should seek the advice of an experienced and knowledgeable consultant who can help them determine whether riparian forest buffers are appropriate, design the most effective plantings, and work with local regulatory agencies to get a project approved. In the right circumstances, a carefully designed buffer can benefit the site owner and the entire community.