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

Water quality improvement
Water quality benefits of restoring riparian buffers are
medium to high. The amount of benefit is based on flow
characteristics and nutrient, sediment, and pollutant
loadings of the runoff as well as the length, slope, type,
and density of vegetation in the riparian buffer.
Runoff entering Zone 3 filters sediment, begins nutrient
uptake, and converts concentrated flow to uniform,
shallow sheet flow. Zone 2 provides contact time and
carbon energy sources in which buffering processes
can take place. It also provides long-term sequestering
of nutrients. Zone 1 provides additional soil and
water contact area to further facilitate nutrient buffering
processes, provides shade to moderate and stabilize
water temperature, and encourages production of beneficial
algae.
Maintenance
An effective riparian buffer restoration project should
include stewardship guidelines to manage and maintain
the site in perpetuity. The most critical period of
riparian buffer establishment is canopy closure, which
is typically the first three to five years after saplings are
planted. Buffer boundaries should be well defined with
clear signs or markers. During this time, the riparian
buffer should be monitored four times annually (February,
May, August, and November are recommended)
and inspected after any severe storm. Maintenance
measures that should be performed regularly include:
1. Watering
• Plantings need deep, regular watering during the
first growing season, either natural watering via
rainfall, or planned watering via caretaker.
• Planting in the fall increases the likelihood of
sufficient rain during planting establishment.
2. Mulching
• Mulch provides moisture retention in the root
zone of plantings, or potentially impacted
vegetation from construction, moderate soil
temperature, and some weed suppression.
• Use coarse, organic mulch that is slow to
decompose in order to reduce the need for repeat
application.
• Apply a two to four-inch layer, leaving air space
around tree trunk to prevent fungus growth.
• Use a combination of woodchips, leaves, and
twigs that have been stockpiled for six months to
a year.
3. Weed and invasive plan control
• Invasive plants can overrun even a welldesigned
planting. It is essential that there is a
plan in place to monitor and remove invasive
vegetation as the planting matures. Use the
Nature Conservancy’s Global Invasive Species
Team Web page as a resource for management
techniques. (http://tncweeds.ucdavis.edu/
esadocs.html) Non-chemical weed control
methods are preferred since chemicals can easily
be washed into the stream.
• Herbicides
Using herbicides is a short-term maintenance
technique (two to three years) that is generally
considered less expensive and more flexible than
mowing and will result in a quicker establishment
of the buffer. Consider and evaluate the proximity
of herbicide use to water features.
• Mowing
Mowing controls the height of the existing
grasses, yet increases nutrient uptake. Therefore,
competition for nutrients will persist until
the canopy closure shades out lower layers
of growth. A planting layout similar to a grid
format will facilitate ease of mowing, but will
yield an unnaturally spaced community. Mowing
may result in strikes to tree trunks unless
protective measures are used. Mowing should
occur twice each growing season. Mower height
should be set between eight and12 inches.
• Weed mats
Weed mats are geo-textile fabrics used to
suppress weed growth around newly planted
vegetation by blocking sunlight and preventing
seed deposition. Weed mats are installed after
planting, and should be removed once the trees
have developed a canopy that will naturally
shade out weeds.
LID Manual for Michigan – Chapter 7 Page 277