RIPARIAN BUFFERS

A riparian buffer is an area of permanent vegetation along the banks of a stream. This mix of native trees, shrubs, grasses, and wetland plants serves to trap and filter pollutants and sediment out of stormwater runoff before it enters the stream. Roots absorb fertilizers and other pollutants. Forest floor bacteria convert harmful nitrates into nitrogen gas that is released into the air.

The root system of plants can hold stream banks in place and prevent erosion. Riparian buffers also act as sponges to absorb excess water, lessening the intensity of flood events and diminishing the force of floodwater. Trees shade the stream, regulating water temperature and improving living conditions for aquatic organisms. Tree leaves fall into the stream where they provide food and habitat for insects, amphibians, crustaceans and small fish critical to the aquatic food chain. Riparian buffers also provide food and cover for wildlife

Increased volume and velocity of stormwater runoff resulting from urbanization can cause stream banks to erode, especially when the native riparian vegetation has been removed. The traditional way to stabilize eroded banks has been with large stone rip-rap or concrete. However, these techniques do not respect the natural hydrology or cross section of the stream. Restoring the stream's natural cross section, minimizing the use of rock and concrete and using native plant materials to stabilize stream banks is a sounder strategy that respects the natural character of the stream and minimizes downstream problems. Unstable, undercut and eroded banks can be reshaped to a more natural contour. Stream banks can be stabilized by using biodegradable matting and planting with supple riparian shrubs such as willows and red osier or gray twig dogwoods. These plants have deep roots to help stabilize the stream bank and supple above-ground growth to allow for bending in the event of flooding. Stream banks can be reinforced with a "biolog" made of processed coconut husk fiber to prevent undercutting by holding soils and plants in place. Stream banks subject to higher water velocities can be protected with large stones placed in the toe of the slope of the streambed.