Low Impact Development Manual for Michigan - OSEH - University ...

Description and Function
A riparian buffer is a permanent restoration area of
trees, shrubs, and herbaceous vegetation adjacent to
a waterbody that serves to protect water quality and
provide critical wildlife habitat. A riparian buffer can
be designed to intercept surface runoff and subsurface
flow from upland sources for the purpose of removing or
buffering the effects of associated nutrients, sediment,
organic matter, pesticides, or other pollutants prior to
entry into surface waters and groundwater recharge
areas.
The riparian buffer is most effective when used as a
component of a sound land management system including
nutrient management and runoff and sediment and
erosion control practices. Use of this practice without
other runoff and sediment and erosion control practices
can result in adverse impacts on riparian buffer vegetation
and hydraulics including high maintenance costs,
the need for periodic replanting, and the flow of excess
nutrients and sediment through the buffer.
Riparian buffer restoration areas consist of three distinct
zones and can be designed to filter surface runoff as sheet
flow and down-slope subsurface flow, which occurs as
shallow groundwater. For the purposes of these buffer
strips, shallow groundwater is defined as saturated
conditions which occur near or within the root zone
of trees and other woody vegetation and at relatively
shallow depths where bacteria, low oxygen concentrations,
and soil temperature contribute to denitrification.
Riparian buffers are designed to encourage sheet flow
and infiltration and impede concentrated flow.
Buffer widths and vegetation types
When developing specific widths for riparian buffers
(Figure 7.45), keep site specific factors in mind, and use
exact measurements as a guide for each site. Various
buffer widths and vegetation types may be appropriate
depending on:
• Project goals,
• The natural features of the river valley, wetlands,
lake, and floodplain, and
• Wildlife habitat requirements.
Buffer averaging and minimum
distances
Buffer ordinances that set specific and minimum buffer
dimensions allow the local government to accept buffer
averaging in order to accommodate variability in terrain
or development plans. For example, a wetland normally
entitled by ordinance to a 75-foot minimum buffer
may be able to tolerate a 50-foot buffer over part of its
margin if a wider buffer is provided along another part.
This depends upon such issues as water flow, topography,
habitat, and species needs, and other factors that
can best be assessed on a case-by-case basis.
Port Townsend, Washington allows buffer averaging if
the applicant demonstrates that the averaging will not
adversely affect wetland functions and values, that the
aggregate area within the buffer is not reduced, and
that the buffer is not reduced in any location by more
than 50 percent or to less than 25 feet.
Woodbury, Minnesota allows buffer averaging where
averaging will provide additional protection to the
wetland resource or to environmentally valuable adjacent
uplands, provided that the total amount of buffer
remains the same.
Source: Environmental Law Institute
Native pond edge
Source: JFNew
LID Manual for Michigan – Chapter 7 Page 269