Transient storage in Appalachian and Cascade mountain streams as related to hydraulic characteristics

Hydraulic characteristics were measured in artificial streams and in 1st- to 5th-orderstreams in the Appalachian and Cascade mountains. Appalachian Mountain stream sites at CoweetaHydrologic Laboratory, North Carolina, were on six 1st-order streams and a 1st- through 4th-ordergradient of Ball Creek-Coweeta Creek. Cascade Mountain sites were located on constrained andunconstrained reaches of Lookout Creek, a 5th-order stream in H. J. Andrews Experimental Forest,Oregon. At each site, a tracer solution (chloride or rhodamine WT) was released for 30-180 minand then discontinued. At the downstream end of the release site, 'the resulting rise and fall of thetracer concentration was measured. These data, along with upstream concentration and measuredwidths 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 fromnear zero in artificial streams to 2.0 m' in 5th-order streams. A, was largest relative to surface cross-sectional area (A) at 1st-order sites where it averaged 1.2 x A, compared with 0.6 x A and 0.1 xA in unconstrained and constrained 5th-order sites, respectively. Where measured, lateral dischargeinputs per metre of stream length ranged from 1.9% of instream discharge in 1st-order streams to0.05% of instream discharge at 5th-order sites. Our results show that surface water exchange withstorage zones is rapid and extensive in steep headwater streams and less extensive but still significantat 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 assistcomparisons of solute dynamics in physically diverse streams.
Key words: solutes, transient storage, transport model, retention, discharge, geomorphology.