Town of Chapel Hill
Field Procedures for Classification of Streams
(For use only by trained staff of the Town Engineering Department)
Prepared: October 20, 2003
Revised: October 31, 2003
This document is a technical supplement to the Chapel Hill Land Use Management Ordinance (LUMO). It describes the criteria and procedures used by Town staff for classifying streams within the Town’s Planning Jurisdiction.
Due to variability in natural stream characteristics, some stream segments may not precisely match the stream definitions and verification criteria in the Town’s Land Use Management Ordinance. These could include stream segments that have been significantly altered or degraded due to urbanization or other anthropogenic activities within the watershed, and/or stream systems with natural variants. 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 in accordance with the following criteria and procedures.
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, some stream segments will not precisely fit the stream definitions and verification criteria found in the LUMO. Natural variant stream segments will be field delineated by Town staff, and will be 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, due to a poorly developed channel, score below 19 points using the above referenced evaluation methods..
b. Discontinuous stream channels that appear to be a functioning component of a stream network but score below 19 points using the above referenced evaluation methods. A discontinuous stream channel is a segment in which there is evidence that base flow continues down-slope, although not in a well-defined channel, and maintains a continuous hydrologic connection between well-defined channel segments upslope and down-slope. The base flow may occur underground as a concentrated flow or a dispersed flow in a course-textured sediment deposit. The discontinuous segment in question shall be classified the same as the stream segment immediately upslope.
c. Stream segments where the grade or slope flattens out causing sediment deposition and/or diffuse flow resulting in a score below 19 points using the above referenced evaluation methods.
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 precisely meet LUMO stream definitions and/or verification criteria. With the exception of relocated streams, these channels will follow the natural drainage-way 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 of, within, and downstream of the segment in question. Common examples include:
a. Well developed stream channels that exhibit “moderate or strong” primary geomorphic and hydrologic indicators, and biological indicators are “absent or weak” due to accelerated channel erosion/ scouring and/or degraded water quality.
b. Geologically young intermittent stream segments that have formed due to increased stormwater runoff, often exhibiting headcuts that have moved rapidly upslope. Such stream segments typically include deeply incised channels with soil indicators of frequent, continuous flow; “weak or moderate” geomorphic and hydrologic indicators; and “absent or weak” biological indicators as described on the stream classification form.
c. Stream origins located at stormwater outlets (pipes, channels, etc.) where increased and concentrated stormwater flow has created a stream channel that likely did not exist previously. These stream segments often exhibit “moderate or strong” geomorphic and hydrologic indicators, but are not shown on map references.
d. Modified natural streams with man-made alterations (such as channelization, armoring, or relocation) that do not precisely meet the LUMO stream definitions and/or verification criteria and is clearly not a man-made ditch or canal. .
5. Stream break-points and origins: When classifying a stream, breakpoints and/or origins may be found along its length. Break-points are locations where the stream classification (type) changes. Origins are the beginning points of streams and/or stream segments. Break-points and origins will be identified during field evaluations and will be clearly staked, flagged and labeled in the field and their approximate location(s) will be indicated on a field map.