A modelling study of hyporheic exchange pattern and the sequence, size, and spacing of stream bedforms in mountain stream networks, Oregon, USA

Studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale, namely slope breaks in the longitudinal profile of streams that generate subsurface head distributions. We recently completed a field study that suggested channel unit spacing in stream longitudinal profiles can be used to predict the spacing between zones of upwelling (flux of hyporheic water into the stream) and downwelling (flux of stream water into the hyporheic zone) in the beds of mountain streams. Here, we use two-dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of stream flow in second-, third-, and fourth-order mountain stream reaches. Modelling allowed us to (1) represent visually the effect that the shape of the longitudinal profile has on the flow net beneath streambeds; (2) isolate channel unit sequence and spacing as individual factors controlling the depth that stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones; (3) evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real streams. We simulated hyporheic exchange in two sets of idealized stream reaches and one set of observed stream reaches. Idealized profiles were constructed using regression equations relating channel form to basin area. The size and length of channel units (step size, pool length, etc.) increased with increasing stream order. Simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased (from 2Ð 7mt o 7 Ð6 m), and downwelling lengths increased (from 2Ð 9mt o 6 Ð0 m) with increase in stream order from second to fourth order. Step spacing in the idealized reaches increased from 5Ð 3mt o 13Ð7 m as stream size increased from second to fourth order. Simulated downwelling lengths increased from 4Ð 3m in second-order streams to 9Ð7 m in fourth-order streams with a POOL–RIFFLE–STEP channel unit sequence, and increased from 2Ð 5m to 6 Ð1 m from second- to fourth-order streams with a POOL–STEP–RIFFLE channel unit sequence. Upwelling lengths also increased with stream order in these idealized channels. Our results suggest that channel unit spacing, size, and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling. Though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed stream reaches than in idealized stream reaches, similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches. This article replaces a previously published version (Hydrological Processes, 19(17), 2915–2929 (2005) [DOI:10.1002/hyp.5790]. Copyright  2006 John Wiley & Sons, Ltd.

[1]  Frederick J. Swanson,et al.  Seasonal and Storm Dynamics of the Hyporheic Zone of a 4th-Order Mountain Stream. I: Hydrologic Processes , 1996, Journal of the North American Benthological Society.

[2]  F. Swanson,et al.  Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon , 1990 .

[3]  F. Triska,et al.  Denitrification in sediments from the hyporheic zone adjacent to a small forested stream , 1990 .

[4]  Michael N. Gooseff,et al.  Comparing transient storage modeling and residence time distribution (RTD) analysis in geomorphically varied reaches in the Lookout Creek basin, Oregon, USA , 2003 .

[5]  Colin R. Townsend,et al.  The Patch Dynamics Concept of Stream Community Ecology , 1989, Journal of the North American Benthological Society.

[6]  K. Bencala.  Interactions of solutes and streambed sediment: 2. A dynamic analysis of coupled hydrologic and chemical processes that determine solute transport , 1984 .

[7]  A. Chin.  The morphologic structure of step–pools in mountain streams , 1999 .

[8]  P. Mulholland,et al.  Evidence that hyporheic zones increase heterotrophic metabolism and phosphorus uptake in forest streams , 1997 .

[9]  L. E. Asmussen,et al.  Vertical Hydrologic Exchange and Ecological Stability of a Desert Stream Ecosystem , 2007 .

[10]  F. Hauer,et al.  Benthic responses to groundwater–surface water exchange in 2 alluvial rivers in northwestern Montana , 2002, Journal of the North American Benthological Society.

[11]  D. McKnight,et al.  Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys , 2002 .

[12]  Don W. Duckson,et al.  Channel bed steps and pool shapes along Soda Creek, Three Sisters Wilderness, Oregon , 2001 .

[13]  M. E. Campana,et al.  ALLUVIAL CHARACTERISTICS, GROUNDWATER–SURFACE WATER EXCHANGE AND HYDROLOGICAL RETENTION IN HEADWATER STREAMS , 1997 .

[14]  Arlen W. Harbaugh,et al.  User's documentation for MODFLOW-96, an update to the U.S. Geological Survey modular finite-difference ground-water flow model , 1996 .

[15]  C. Welty,et al.  Stream-groundwater interactions: The influence of aquifer heterogeneity and stream meandering on 2-D and 3-D hyporheic exchange flows , 2003 .

[16]  Vitaly A. Zlotnik,et al.  Three‐dimensional model of modern channel bend deposits , 2003 .

[17]  Roy Haggerty,et al.  Power‐law residence time distribution in the hyporheic zone of a 2nd‐order mountain stream , 2002 .

[18]  S. Findlay.  Importance of surface‐subsurface exchange in stream ecosystems: The hyporheic zone , 1995 .

[19]  J. T. Hack.  Studies of longitudinal stream profiles in Virginia and Maryland , 1957 .

[20]  C. Baxter,et al.  Geomorphology, hyporheic exchange, and selection of spawning habitat by bull trout (Salvelinus confluentus) , 2000 .

[21]  Jeremy B. Jones,et al.  Nitrification in the Hyporheic Zone of a Desert Stream Ecosystem , 1995, Journal of the North American Benthological Society.

[22]  A. Chin.  The periodic nature of step-pool mountain streams , 2002 .

[23]  R. Haggerty,et al.  Patterns in stream longitudinal profiles and implications for hyporheic exchange flow at the H.J. Andrews Experimental Forest, Oregon, USA , 2005 .

[24]  K. Bencala,et al.  The Effect of streambed topography on surface‐subsurface water exchange in mountain catchments , 1993 .

[25]  K. Bencala,et al.  Hyporheic zone hydrological processes , 2000 .

[26]  David W. Pollock,et al.  User's guide for MODPATH/MODPATH-PLOT, Version 3; a particle tracking post-processing package for MODFLOW, the U.S. Geological Survey finite-difference ground-water flow model , 1994 .

[27]  D. Dudley Williams,et al.  Factors controlling riffle‐scale hyporheic exchange flows and their seasonal changes in a gaining stream: A three‐dimensional groundwater flow model , 2003 .

[28]  S. Wondzell,et al.  Geomorphic controls on hyporheic exchange flow in mountain streams , 2003 .

[29]  M. Dobson,et al.  Role of interaction zones between surface and ground waters in DOC transport and processing: considerations for river restoration , 1993 .

[30]  D. Geist.  Hyporheic discharge of river water into fall chinook salmon (Oncorhynchus tshawytscha) spawning areas in the Hanford Reach, Columbia River , 2000 .

[31]  D. Montgomery,et al.  Channel-reach morphology in mountain drainage basins , 1997 .

[32]  W. Woessner.  Stream and Fluvial Plain Ground Water Interactions: Rescaling Hydrogeologic Thought , 2000 .

[33]  G. Minshall,et al.  The River Continuum Concept , 1980 .