Field Procedures for Classification of Streams
(Based on recommendations developed by the Town of
Introduction
This document has been developed
as a technical reference to the Chapel Hill Land Use Management Ordinance for
the purpose of providing criteria and procedures that will be used by Town
staff for classifying intermittent and perennial streams within the Town of
Due to variability in natural
characteristics and urbanization, some stream segments may not clearly match
the stream definitions and verification criteria in the Town’s Land Use
Management Ordinance. This would include
stream segments that have been significantly altered or degraded due to
urbanization or other anthropogenic activities.
Such stream segments, provided that they are functioning components of an
otherwise classified stream network, shall be included in the stream
classification in accordance with the Land Use Management Ordinance and
following the procedures outlined in this document.
Stream Classification Criteria and Procedures
1. Intermittent Stream
Field Evaluation Method: Using the
current version of the North Carolina Division of Water Quality (NCDWQ) Stream
Classification Method and the associated Internal Guidance Manual, a stream or
stream segment must score a minimum of 19 points for classification as “intermittent”.
For scores of 18 points or less, the stream will be classified as “ephemeral”
unless found to be a natural variant or urbanized channel as described below.
2. Perennial Stream Field Evaluation Method: Using the current version of the NCDWQ Stream Classification Method and the associated Internal Guidance Manual, a stream or stream segment must score a minimum of 30 points for classification as “perennial”.
3. Natural Variant Streams: Due to the broad variability in the natural characteristics of small streams, there are a number of types of stream segments at the origin or downstream of the origin, that do not fit the stream determination criteria, yet are a functioning component of the stream network. Such variant stream segments shall be field delineated, and classified the same as the stream segment immediately downstream for headwater segments; or immediately upstream for other than headwater segments. Common examples include:
a. Small streams within or fed by natural springs, slope wetlands or groundwater seeps that present evidence of near perennial or perennial flow but score below 19 points using the above referenced evaluation methods due to a poorly developed channel.
b. Discontinuous stream channels that appear to be a functioning component of the stream network and score below 19 points using the above referenced evaluation methods. The discontinuous segment in question shall be classified the same as the stream segment immediately upstream.
c.
Stream segments where the grade or slope flattens out causing
sediment deposition and/or diffuse flow resulting in a score below 19 points.
4. Urbanized Channels: The impacts of urbanization and other anthropogenic activities may result in alteration or degradation of a stream or stream segment to the extent that it does not clearly meet stream classification definitions and/or verification criteria. With the exception of relocated streams these channels will follow the natural drainageway to distinguish them from ditches and canals. Such channels and/or channel segments shall be classified based on all available evidence including field investigation and map resources upstream, within, and downstream of the segment in question. Common examples include:
a. Well developed stream channels that appear to be perennial streams, but benthic macroinvertebrate indicators are lacking due to accelerated channel erosion and scouring or degraded water quality.
b. Geologically very young intermittent stream segments that have formed due to greatly increased stormflow or where headcuts have moved rapidly upslope. Such streams often have deeply incised channels with soil indicators of frequent, continuous flow, but lack many of the geomorphic indicators (riffle and pool systems, benches or bars, etc.) and many of the biological indicators of natural streams.
c. Stream origins located at stormwater outlets where greatly increased stormflow has produced a stream channel where a stream was not previously present. Often, such stream segments clearly exhibit the characteristics of intermittent or perennial streams but are not shown on maps.
d. Modified natural streams with man-made alterations such as channelization, armoring, or relocation that do not meet the criteria for an intermittent or perennial stream.
5. Stream break-points:
When classifying a stream, a breakpoint(s) may be found along its length. Break-points
are locations where the stream classification (type) begins or ends. Break-point
features that are identified during field evaluations will be clearly staked, flagged
and labeled in the field and their approximate location(s) will be indicated on
a field map.
6. The Town Board of
Adjustment will hear appeals of stream determinations performed by Town staff.