WHAT IS A STREAM?

Implementation of rules in 1997 for protection of existing forested riparian buffers on intermittent and perennial streams in North Carolina has raised many questions related to defining and identifying small streams on the landscape. The central issue is: how far upstream in the small streams of a stream network should buffers be maintained in order to take maximum advantage of the nutrient reduction functions of the riparian zone and the stream? Thus the principal question addressed in the work reported here is: what is a stream? or more precisely, what is the origin on the landscape of the minimum functioning stream? These questions resulted in a three stage process to define stream types and to develop field procedures to determine stream locations and origins:Detailed stream definitions were developed and incorporated into the permanent Neuse River Basin riparian buffer rules.Field procedures for determining the origins of intermittent streams were developed and have been tested extensively throughout the state. Biotic indicators for determining the origins of perennial streams have also recently been developed and are undergoing testing in the Piedmont province of the state (Lawson, et al., 2002).Research was initiated to:Determine the types and level of errors in US Geological Survey (USGS) 1:24,000 scale maps and Natural Resources Conservation Service (NRCS) County Soil Survey maps in depiction of intermittent and perennial streams;Determine the size and geomorphic characteristics of subwatersheds that produce intermittent streams.Attempt to develop desktop procedures that can be used to accurately determine intermittent stream origins on USGS maps.The field procedure for determining intermittent stream origins, dubbed the Stream Evaluation Procedure, consists of evaluating geomorphic, soils, hydrologic, and biotic characteristics of the stream channel and stream corridor. The procedure works well in all three physiographic provinces of North Carolina, the Coastal Plain, the Piedmont, and Mountains. With training and experience, agency personnel and consultants can determine intermittent stream origins with consistency. To extend the intermittent stream origin procedure to perennial stream origins, an addition to the Stream Evaluation Procedure that uses aquatic biota indicators of perennial flow is undergoing testing in the Piedmont region.The research element of this series of projects has resulted in the following conclusions:USGS 1:24,000 topographic maps in North Carolina significantly underestimate the presence of intermittent streams throughout most of state except for the Coastal Plain.NRCS Soil Survey maps tend to overestimate the presence of intermmittent streams throughout the state.In the Piedmont province, the size of the stream-forming subwatershed (i.e., watersheds upstream of intermittent stream origins) averaged just 6 ha, with a range of 2–26 ha.In the mountain region, a significant proportion of first order streams originate as small perennial streams that are fed by springs.