TRANSIENT STORAGE IN APPALACHIAN AND CASCADE MOUNTAIN STREAMS AS RELATED TO HYDRAULIC CHARACTERISTICS

Hydraulic characteristics were measured in artificial streams and in l st- to 5th-order streams in the Appalachian and Cascade mountains. App alachian Mountain stream sites at Coweeta Hydrologic Laboratory, North Carolina, were on six 1st-order streams and a 1st- through 4th-order gradient of Ball Creek-Coweeta Creek. Cascade Mountain sites were loca ted on constrained and unconstrained reaches of Lookout Creek, a 5th-o rder stream in H. J. Andrews Experimental Forest, Oregon. At each site , a tracer solution (chloride or rhodamine WT) was released for 30-180 min and then discontinued. At the downstream end of the release site, the resulting rise and fall of the tracer concentration was measured. These data, along with upstream concentration and measured widths and depths, were used in a computer model to estimate several hydraulic p arameters including transient storage and lateral inflow. Estimated tr ansient storage zone size (A(s)) ranged from near zero in artificial s treams to 2.0 m2 in 5th-order streams. A, was largest relative to surf ace cross-sectional area (A) at 1st-order sites where it averaged 1.2 x A, compared with 0.6 x A and 0.1 x A in unconstrained and constraine d 5th-order sites, respectively. Where measured, lateral discharge inp uts per metre of stream length ranged from 1.9% of instream discharge in 1st-order streams to 0.05% of instream discharge at 5th-order sites . Our results show that surface water exchange with storage zones is r apid and extensive in steep headwater streams and less extensive but s till significant at 3rd- through 5th-order sites. An understanding of relationships between stream morphology, storage zone size, and extent of interactions between surface and subsurface waters will assist com parisons of solute dynamics in physically diverse streams.