Agenda - 06-01-2010 - 6a - Laserfiche WebLink

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100 Stream Network Elements Defined Stream order — A system for designing the relative location of a stream within a stream network and the degree of branching of the stream network within a watershed. The most upstream, unbranched stream segments (intermittent or perennial) are denoted as first order. A segment is denoted as second order where two first order streams (or segments) join. A segment is denoted as third order where two second order segments join, etc. By convention, stream order is labeled in accordance with the streams depicted on a USGS 1:24,000 scale map (Figure 1). Note that low order streams (first or second) often discharge directly to much larger and higher order streams. In the example of Figure 1, several first order streams discharge directly to the fourth order steam reach near the mouth of the drainage basin. However, those first order streams still meet my definition of headwaters stream. 4 0 0.5 LO 1. km 1 kr' 1:'� 3 1' 1 2/1 \; , 1 12 it 2 . 2 12 . 1 i• :1 1 ' Figure 1. Diagram of a Piedmont watershed illustrating the procedure for designating stream order. In terms of the regulatory application of the stream origin and stream corridor functions discussed in this training program, I also offer the concept of the "regulatory stream origin ". Identifying an intermittent or perennial stream origin in the field is an opinion based on best professional judgment. However, the stream definitions outlined below that have been adopted by the NC Environmental Commissions and the procedures for applying those definitions in the field are based on the following policy: The origin of a regulated stream is the most upstream point on a first order stream where the ecological functions of a stream are present and operating at a minimal level. S: \2_Boards \BOCC \2010 BOCC Agendas \6 -1 -10 \Upper Eno Critical Area Amendments\Att 8\Att 8.4 -Stream Order Info.doc