Buffer Area Delineation
Following a review of all applicable ordinances and the delineation of the stream or lake
shoreline, the next step in determining whether a buffer applies to a parcel of land is the
delineation of the buffer area on the ground. If this buffer area does not cross the parcel of land,
then the buffer does not apply. In some situations, only the buffer and not the stream may be
located on a parcel of land in which case the buffer will apply. Structures existing at the time the
buffer ordinance was adopted are exempt from buffer requirements and may remain in place.
Expansions and/or redevelopment that impact the buffer may be prohibited, therefore it is
essential to know the extent of the buffer on the ground to determine if it will be impacted.
All water quality buffers are measured horizontally on a line perpendicular to the surface water.
For lakes, this measurement is made landward from the full pond elevation described in the
previous subsection. For streams and the ponds that they intersect, buffers are measured
landward from the top of the bank on both sides of the stream as illustrated by Figure 1. The
bank of a stream or pond is the vertical or sloped area rising from the channel where normal or
base flow occurs. The top of the bank is considered the most landward location of the bank of
the stream or pond, which is typically where rooted herbaceous vegetation begins to become
established. The stream bank provides the lateral constraints for all stages of flow except for the
flood stage when flows spill over into the floodplain. Typically there is a topographic break
between the steep stream bank and the flatter floodplain. This break usually characterizes the top
of the bank from where buffer widths are measured. The slope and configuration of the stream
bank can vary significantly depending on flow, soil type and topography. In urban streams that
are highly eroded, the stream bank may rise almost vertically from the stream channel. In more
rural settings, the bank may rise much more gently. According to all buffer rules, the delineation
of the buffer on the ground must be performed by a registered land surveyor. POLARIS or any
other GIS coverage as well as USGS quadrangle maps cannot be used to establish a buffer width
since it is impossible to account for slope. In addition, the buffers shown in POLARIS as
illustrated in Figure 1 are not to scale and cannot be used to determine the exact location of a
buffer on the ground surface.
Figure 1: Buffer Area Measurement
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Existing Impervious Cover
For all buffer types, structures and other impervious cover such as parking lots, etc. as well as
uses such as lawns, agriculture etc. that were present within the stream or lake buffer as of the
effective date of the applicable ordinance and have continued to exist since that time are exempt
from ordinance requirements. For S.W.I.M. and post-construction buffers, the redevelopment or
expansion of such structures and other impervious cover is also exempt from buffer requirements
provided it does not result in an increase in the total impervious area within the buffer. For water
supply watershed buffers, any redevelopment or rebuilding activity involving an existing
structure that requires a building permit is not allowed. For buffers in Goose and Six Mile
Creeks, the redevelopment of an existing structure is exempt from buffer requirements provided
the following conditions are met:
• The redevelopment occurs on the same footprint as the existing development.
• Existing storm water controls remain, including diffuse flow conditions.
• The redevelopment of nonresidential structures results in the disturbance of less than a
half acre.
• The site remains vegetated in a manner similar to existing conditions.
• Applicable storm water control requirements are met.
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