1. BMP 5.4.2: Protect /Conserve/Enhance Riparian Areas
      1. Potential Applications
      2. Key Design Elements
      3. Stormwater Functions
      4. Water Quality Functions
      5. Detailed Stormwater Functions
      6. Design Considerations/Variations
      7. Construction Issues
      8. Cost Issues
      9. Stormwater Management Calculations
      10. Specifications

BMP 5.4.2: Protect /Conserve/Enhance Riparian Areas
The Executive Council of the Chesapeake Bay Program
defines a Riparian Forest Buffer as "an area of trees, usually
accompanied by shrubs and other vegetation, that is adjacent
to a body of water and which is managed to maintain the
integrity of stream channels and shorelines, to reduce the
impact of upland sources of pollution by trapping, filtering and
converting sediments, nutrients, and other chemicals, and to
supply food, cover, and thermal protection to fish and other
Potential Applications
Commercial: Ultra
Urban: Industrial:
Yes Yes
Yes Yes
Yes Yes
Key Design Elements
Stormwater Functions
Volume Reduction:
Peak Rate Control:
Water Quality:
Very High
Water Quality Functions
Linear in Nature
Provide a transition between aquatic and upland environments
Forested under natural conditions in Pennsylvania
Serve to create a "Buffer" between development and aquatic
Help to maintain the hydrologic, hydraulic, and ecological integrity
of the stream channel.
Comprised of three "zones" of different dimensions:
Zone 1
: Adjacent to the stream and heavily vegetated
under ideal conditions (Undisturbed Forest) to
shade stream and provide aquatic food sources.
Zone 2
: Landward of Zone 1 and varying in width,
provides extensive water quality improvement.
Considered the Managed Forest.
Zone 3
: Landward of Zone 2, and may include BMPs
such as Filter Strips.
There are two components to Riparian Buffers to be considered in the development process:
1. Protecting, maintaining, and enhancing existing Riparian Forest Buffers.
2. Restoring Riparian Forest Buffers that have been eliminated or degraded by past practices.
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BMP 5.4.2 focuses on protection, maintenance, and enhancement of existing Riparian Forest Buffers.
Restoration of Riparian Forest Buffers is treated in Chapter 6 as a Structural BMP.
Figure 5.2-1. Riparian buffer zones support various ecological functions.
Detailed Stormwater Functions
Riparian Corridors are vegetated ecosystems along a waterbody that serve to buffer the waterbody
from the effects of runoff by providing water quality filtering, bank stability, recharge, rate attenuation
and volume reduction, and shading of the waterbody by vegetation. Riparian corridors also provide
habitat and may include streambanks, wetlands, floodplains, and transitional areas. Functions can be
identified and sorted more specifically by Zone designation:
Zone 1
: Provides stream bank and channel stabilization; reduces soil loss and sedimentation/nutrient
and other pollution from adjacent upslope sheet flow; roots, fallen logs, and other vegetative debris
slow stream flow velocity, creating pools and habitat for macroinvertebrates, in turn enhancing
biodiversity; decaying debris provides additional food source for stream-dwelling organisms; tree
canopy shades and cools water temperature, critical to sustaining certain macroinvertebrates, as well
as critical diatoms, which are essential to support high quality species/cold water species. Zone 1
functions are essential throughout the stream system, especially in 1st order streams.
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Zone 2
: Removes, transforms, and stores nutrients, sediments, and other pollutants flowing as sheet
flow as well as shallow sub-surface flow. A healthy Zone 2 has the potential to remove substantial
quantities of excess nitrates through root zone uptake. Nitrates customarily can be significantly
elevated when adjacent land uses are agricultural or urban/suburban. Healthy vegetation in Zone 2
slows surface runoff while filtering sediment and particulate bound phosphorus. Total nutrient removal
is facilitated through a variety of complex processes: long-term nutrient storage through microbe
uptake, denitrification through bacterial conversion to nitrogen gases and additional microbial
degradation processes.
Zone 3
: Provides the first stage in managing upslope runoff so that runoff flows are slowed and evenly
dispersed into Zone 2. Some physical filtering of pollutants may be accomplished in Zone 3 as well as
some limited amount of infiltration.
Figure 5.2-2. Riparian buffer zones (DJ Welsh, 1991).
Design Considerations/Variations
Although this manual refers frequently to the Chesapeake Bay Program’s Riparian Handbook, many
different sources of guidance have been developed in recent years. Not all of these are exactly
comparable in terms of their recommendations and specifications. To some extent these variations
relate to different land use development contexts.
Riparian Forest Buffer Zone widths should be adjusted according to site conditions and type of upslope
development. Variation in standards (see Specifications below) should vary with the function to be
performed by the forested buffer. In undisturbed forested areas where minimal runoff is expected to be
occurring, standards can be made more flexible than in agricultural contexts where large quantities of
natural vegetation have been removed and significant quantities of runoff are expected. In addition to
factors related to technical need, practical and political factors also must be considered. In urbanized
settings where hundreds, if not thousands of small lots may abut riparian areas and already intrude into
potential forested buffer zones, buffer standards must be practicable.
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Figure 5.2-3. Riparian buffer zone functions.
Lastly, confusion has emerged
between the concept of
floodplain and riparian forest
buffer. In many cases,
mapped and delineated
floodplain may overlap and
even largely coincide with
riparian forest buffer zones.
On the other hand, mapped
100-year floodway/floodplain
may not coincide with the
forest buffer due to either very
steep topography or very
moderate slopes. A second
important clarification is that
floodplain ordinances typically
manage use to prevent flood
damage, which contrasts to
riparian forest buffer regulation
which manages clearing and
grading actions in the zones, specifically for environmental reasons.
Construction Issues
Riparian Forest Buffer Protection should be defined and included in municipal ordinances, including
both the zoning ordinance and subdivision and land development ordinance (SALDO). The Riparian
Forest Buffer should be defined and treated from the initial stages of the land development process,
similar to floodplain, wetland or any other primary conservation value. It is the municipality’s
responsibility to determine a fair and effective riparian forest buffer program, balancing the full range of
water resource and watershed objectives along with other land use objectives. A fair and effective
program should evolve for all municipal landowners and stakeholders. State-supported River
Conservation Plans, Act 167 Stormwater Management Plans, and other planning may contribute to this
Whether a respective municipality has included riparian forest buffers in its ordinances or not,
landowners/developers/applicants should include riparian forest buffers in their site plans from the
initiation of the site planning process. If standards and guidelines have been set forth by the
municipality or by other relevant planning group, these standards and guidelines should be followed. If
none of these exist, standards recommended in this manual should be followed.
The ease of accommodating a riparian forest buffer can be expected to vary based on intensity of land
use, zoning at the site and size of the parcel. Holding all other factors constant, as site size decreases,
the challenges posed by riparian zone accommodation can be expected to increase. As sites become
extremely small, reservation of site area for riparian forest buffer may become problematic, thereby
requiring riparian forest buffer modification in order to accommodate a reasonable building program for
the site. Zoned land use intensity is another factor to be considered. As this intensity increases and
specifications for maximum building area and impervious area and total disturbed area are allowed to
grow larger, reserving site area for the riparian forest buffer becomes more challenging. Riparian forest
buffer programs need to be sensitive to these constraints.
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All of these factors should be reviewed and integrated by the municipality as the riparian forest buffer
program is being developed.
Cost Issues
Costs of riparian forest buffer establishment are not significant, defined in terms of direct development.
In these cases, costs can be reasonably defined as the lost opportunity costs of not being able to use
acreage reserved for the riparian forest buffer in the otherwise likely land use. A likely land use might
be defined in terms of zoned land use. Depending upon the zoning category provisions and the degree
to which a riparian forest buffer’s Zone 1 or Zone 2 or Zone 3 might be able to be included as part of a
land development plan or as part of yard provisions for lots in a residential subdivision acreage included
within the riparian forest buffer may or may not be able to be included as part of the development. If
riparian acreage must be totally subtracted, then it’s fair value should be assessed as a cost. If riparian
forest buffers can be credited as part of yards (though still protected), then that acreage should not be
considered to be a cost. Any one-time capital cost can be viewed alternatively as an annualized cost.
To the extent that the riparian forest buffer coincides with the mapped and regulated floodplain, where
homes and other structures and improvements should not be located, then attributing any lost
opportunity costs exclusively to riparian forest buffers is not reasonable. The position can be argued
that any riparian forest buffer area, which is included within floodplain limits, should not be double-
counted as a riparian forest buffer cost. Alternatively, any riparian forest buffer area that extends
beyond the floodplain could be assigned a cost.
Lost opportunity costs can be expected to vary depending upon land use. Alternative layouts, including
reduced lot size configurations, may be able to provide the same or close to the same number of units
and the same level of profitability.
Over the long-term, some modest costs are required for periodic inspection of the riparian forest buffer
plus modest levels of maintenance. Generally, the buffers require very little in the way of operating and
maintenance costs.
If objective cost-benefit analysis were to be undertaken on most riparian forest buffers, results would be
quite positive, demonstrating that the full range of environmental and non-environmental benefits
substantially exceeds costs involved. Protection of already existing vegetated areas located adjacent
to streams, rivers, lakes, and other waterways is of tremendous importance, given their rich array of
functional benefits.
Stormwater Management Calculations
Stormwater calculations in most cases for Volume Control and Recharge and Peak Rate will not be
affected dramatically. See Chapter 8 for more discussion relating to Water Quality.
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The Chesapeake Bay Program’s Riparian Handbook provides an in-depth discussion of establishing
the proper riparian forest buffer
width, taking into consideration:
1. existing or potential value of
the resource to be protected,
2. site, watershed, and buffer
3. intensity of adjacent land use,
4. specific water quality and/or
habitat functions desired.
(Handbook, p. 6-1)
At the core of the scientific basis for
riparian forest buffer establishment
are a variety of site-specific factors,
including: watershed condition,
slope, stream order, soil depth and
erodibility, hydrology, floodplains,
wetlands, streambanks, vegetation
type, and stormwater system, all of
which are discussed in the
Handbook. Positively, this body of
scientific literature has expanded
tremendously in recent years and provides excellent support for effective buffer management. The
downside is that this scientific literature now exceeds quick and easy summary. Fortunately, this
Handbook and many additional related references are available online without cost (given the
comprehensiveness of the Handbook itself, it is recommended that the reader start here).
Figure 5.2-4. Three zone urban buffer system (Schueler, 1995 and
Metropolitan COG, 1995).
Zone 1:
Also termed the “streamside zone,” this zone “…protects the physical and ecological integrity
of the stream ecosystem. The vegetative target is mature riparian forest that can provide shade, leaf
litter, woody debris, and erosion protection to the stream. The minimum width is 25 feet from each
streambank (approximately the distance of one or two mature trees from the streambank), and land use
is highly restricted….” (Handbook, p. 11-8)
Zone 2:
Also termed the “middle zone,” this zone”…extends from the outward boundary of the
streamside zone and varies in width depending on stream order, the extent of the 100-year flood plain,
adjacent steep slopes, and protected wetland areas. The middle zone protects key components of the
stream and provides further distance between upland development and the stream. The minimum
width of the middle core is approximately 50 feet, but it is often expanded based on stream order, slope
of the presence of critical habitats, and the impact of recreational or utility uses. The vegetative target
for this zone is also mature forest, but some clearing is permitted for stormwater management Best
Management Practices (BMPs), site access, and passive recreational uses….” (Handbook, p. 11-8)
Zone 3:
Also termed the “outer zone,” this zone “…is the ‘buffer’s buffer.’ It is an additional 25-foot
setback from the outward edge of the middle zone to the nearest permanent structure. In many urban
situations, this area is a residential backyard. The vegetative character of the outer zone is usually turf
or lawn, although the property owner is encouraged to plant trees and shrubs to increase the total width
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of the buffer… The only significant restrictions include septic systems and new permanent structures.”
(Handbook, p. 11-9)
The Handbook also provides more detailed specifications for riparian forest buffers (Appendix 1), as
developed by the USDA’s Forest Service.
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