HR: 1340h
AN: H13D-1536    [Abstracts]
TI: A Comparison of In-Channel Dead Zone and Hyporheic Zone Transient Storage Parameter Estimates Between a 1st and 5th Order Stream
AU: * Briggs, M
EM: mabriggs@mines.edu
AF: Colorado School of Mines, Department of Geology and Geological Engineering 1516 Illinois St., Golden, CO 80401, United States
AU: Gooseff, M
EM: mgooseff@engr.psu.edu
AF: Penn State University, Civil and Environmental Engineering Department 212 Sackett Bldg., University Park, PA 16802, United States
AU: Morkeski, K
EM: kmorkeski@mbl.edu
AF: Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543, United States
AU: Wollheim, W
EM: wi.wollheim@unh.edu
AF: University of New Hampshire, Water Systems Analysis Group, Durham, NH 03824, United States
AU: Hopkinson, C
EM: chopkins@mbl.edu
AF: Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543, United States
AU: Peterson, B
EM: peterson@mbl.edu
AF: Marine Biological Laboratory, 7 MBL St., Woods Hole, MA 02543, United States
AU: Vorosmarty, C
EM: cv@eos.sr.unh.edu
AF: University of New Hampshire, Water Systems Analysis Group, Durham, NH 03824, United States
AB: A major enhancement to our understanding of how watersheds function would be the ability to discriminate between in-channel dead zone ( DZ) and hyporheic zone ( HZ) transient storage, and an evaluation of how these properties scale across stream orders. The nature of DZ storage is to display faster exchange rates with the main channel and less overall sediment contact time than HZ storage. These differences have great significance to many in-stream processes such as nutrient cycling. The combination of high slope, coarse bed material and fluvial structure endemic to many 1st order streams can provide greater forcing of hyporheic flow paths than occurs within the lower gradient 5th order streams. Conversely many 5th order reaches exhibit large side pool and back eddy DZ areas not common along 1st order streams. This study builds on existing methods to delineate the DZ and HZ from the integrated signal of a conservative solute's breakthrough curve ( BTC). Data for this comparison were collected over the summer of 2007 within the Ipswich River watershed, a basin which drains into Plum Island Sound on the north shore of Massachusetts, USA. The conservative solute NaCl was injected into both a 1st order medium gradient stream and a 5th order low gradient stream. The BTCs collected in thalwegs from the NaCl injections were simulated using a version of the solute transport model OTIS containing two zones of transient storage. Hydrometric measurements of stream velocity were used to estimate average main channel cross sectional area ( A) and DZ cross sectional area ( A_SDZ) for each reach to constrain parameter estimates and avoid model equifinality between the storage zones. Initial values for the exchange rate between main channel flow and DZ storage ( α_DZ) were estimated from DZ BTCs. Our results indicate that although the overall storage zone is much larger in proportion to the main channel for the 1st order reach than for the 5th order reach, the percentage of median transport time due to storage as evaluated by the F_MED²⁰⁰ is smaller. Additionally the integrated DZ and HZ α is faster for the 5th order reach, which in agreement with our original hypotheses that DZ storage is the dominant transient storage process in high order streams. Further analysis across stream orders may reveal useful relationships between channel form and hydrologic function.
DE: 1800 HYDROLOGY
DE: 1830 Groundwater/surface water interaction
DE: 1860 Streamflow
SC: Hydrology [H]
MN: 2007 Fall Meeting