Take a Walk on the Science Side:
Why Aquatic Buffer Zones are So Important

by John McFadden, Director of Science & Restoration Programs

Most landowners whose property runs along a river or stream naturally want to be able to enjoy their view of the water. This desire often results in the clearing of trees and mowing the lawn right up to the river’s edge. Often, landowners don’t realize that these efforts to get a better view can result in loss of property through erosion. So what’s the answer to fully enjoying the river while also protecting the river and the land? Aquatic buffers, to use an ecological term.

Defining the Riparian Zone

The streamside or “riparian zone,” is defined as the area from the top of the river’s bank out to 300 feet — in other words, the 300-foot wide strip running alongside the river. The riparian area is critical to the health of the river because it performs three critical ecological tasks: promoting biological diversity, wildlife connectivity, and hydrologic functioning. Attention to these three functions ultimately helps create a healthy aquatic buffer which will enhance long-term enjoyment of the river by the landowner.

Biological Diversity: Land & Water

“Biological diversity” — the variety of plant and animal species — occurs in riparian areas because these streamside areas represent transition zones between two types of environments: land and water. Riparian zones support a wider variety of plants and animals than either the land or the water can. The vegetation along the river, especially deep-rooted trees like the sycamore, helps hold the soil in along the bank, defending your property against erosion. Therefore, it’s a good idea to leave the trees and natural vegetation as an aquatic buffer.

Do not mow right up to the river’s edge! The vegetation also provides cover and food for wildlife, which are necessary components if the wildlife is going to live in and move through these areas. Select some areas of the buffer zone to be landscaped with low growing vegetation and you can still have your “view” while also protecting the health of the river.

Protecting Wildlife Corridors

“Wildlife connectivity” — the ability of animals to move from one habitat area to another — is also crucial to the health of the river system. One of the toughest environmental impacts caused by our society’s sprawl is that wildlife populations become isolated or lose the connecting corridors that they used to rely on to move from one area to another in search of food, shelter and mates.

Animals use river and stream corridors as transportation routes. They need areas that provide cover (such as shrubs) for a place to bed down at night, and they feed on the rich biodiversity associated with streambank areas. Biodiversity and connectivity are promoted by the unique water flow of the riparian zone.

Where Does Flowing Water Go?

“Hydrologic functions” — how the water flows in and through the streamside zone — may be the most important aspect for us to consider when thinking about aquatic buffers. The ability of a river or stream to respond to rainfall and drought without flash flooding or going dry is tied to having an aquatic buffer.

These streamside buffers store water, “recharging” the stream during dry periods and absorbing and storing water (as groundwater) from both rain and from the river itself during wet periods. Parking lots and lawns up to the river’s edge in effect send precious rain downstream versus letting it soak into the ground. Two things happen as a result: streams fill more often and faster which causes banks to erode, and groundwater does not get recharged so streams dry up in the summer and river flows become unnaturally low.

The other very important hydrologic function of the riparian zone is its ability to filter out pollutants from water, usually from rainfall, that enter the area from the surrounding landscape. To do this, stormwater needs to be allowed to dissipate and flow through the riparian zone in a dispersed manner (called “sheetflow”) rather than being funneled through ditches and culverts directly into the stream or river. Concentrating rainwater into culverts is the primary way pollution gets into our rivers and also the main cause of streambank erosion.

This eroding steam bank in Brentwood is one of many HRWA targeted for restoration in 2003.

HRWA’s River Restoration Program

In 2002, HRWA conducted a visual stream survey that identified over 100 sites around our watershed that need restoration. See the cover story for details on the projects our staff and volunteers have undertaken this year. Preserving an aquatic buffer on your property will protect your RIVER and your VIEW. Contact us for more information on plant species appropriate for the streamside zone, for landscaping techniques such as “rain gardens,” development site design approaches, and farm management techniques that can be used to effectively protect river health and enhance property values.

-From Voices for the Harpeth, 2004