Transient Storage in Appalachian and Cascade Mountain Streams as Related to Hydraulic Characteristics

Abstract

Hydraulic characteristics were measured in artificial streams and in lst- to 5th-order streams in the Appalachian and Cascade mountains. Appalachian Mountain stream sites at Coweeta North Carolina, were on six lst-order streams and a lst- through 4th-order gradient of Ball Creek-Coweeta Creek. Cascade Mountain sites were located on constrained and unconstrained reaches of Lookout Creek, a 5th-order stream in H. J. Andrews Experimental Forest, Hydrologic Laboratory, 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 parameters in- cluding transient storage and lateral inflow. Estimated transient storage zone size (A,) ranged from near zero in artificial streams to 2.0 m2 in 5th-order streams. As was largest relative to surface cross- sectional area (A) at lst-order sites where it averaged 1.2 x A, compared with 0.6 x A and 0.1 x A in unconstrained and constrained 5th-order sites, respectively. Where measured, lateral discharge storage zones is rapid and extensive in steep headwater streams and less extensive but still significant at 3rd- through 5th-order sites. An understanding of relationships between stream morphology, inputs per metre of stream length ranged from 1.9% of instream discharge in lst-order streams to 0.05% of instream discharge at 5th-order sites. Our results show that surface water exchange with storage zone size, and extent of interactions between surface and subsurface waters will assist comparisons of solute dynamics in physically diverse streams.