HR: 13:40h
AN: H23J-01 INVITED    [Abstracts]
TI: The influence of small dams on streambed morphology, sediment distribution and fluxes of water, heat and solutes between surface and ground water
AU: * Lautz, L
EM: lklautz@esf.edu
AF: SUNY College of Environmental Science and Forestry, 1 Forestry Dr., Syracuse, NY 13210,
AU: Fanelli, R
EM: rfanelli@syr.edu
AF: SUNY College of Environmental Science and Forestry, 1 Forestry Dr., Syracuse, NY 13210,
AB: Small dams, including natural debris dams and constructed log dams, increase the complexity of streambed morphology and control the localized sediment distribution in streams. To investigate the impact of dams on water, heat and solute fluxes in the streambed, we instrumented a 20 m section of a 2nd order semi-arid stream with temperature data loggers and in-stream mini-piezometers upstream and downstream of a 1.5 m tall constructed log dam. Hydraulic gradients and time-series temperature data in the stream, streambed and groundwater were used to qualitatively and quantitatively assess the direction and rate of water flux through the streambed daily between July of 2006 and June of 2007 and at discrete times during water quality sampling. Spatial variability of stream, streambed, and ground water quality data was used to assess the types and rates of biogeochemical processes occurring in the streambed during October, 2005, and July, 2006. Upstream of the dam, low-velocity pools allow fine sediments to settle out, restricting the flux of water, heat and solutes into the streambed, despite large, negative hydraulic gradients. Downstream of the dam, riffle sequences comprised of coarse sands and cobbles generate relatively rapid fluxes of water, heat and solutes through the shallow streambed, even under smaller hydraulic gradients. As a result, a mosaic of streambed zones with different rates of biogeochemical reactions are created by the constructed log dam and these zones persisted across different seasons of the year. The transport of heat and solutes through the streambed was unique from surface or groundwater heat and solute transport, supporting the view that the streambed is a unique hydrologic zone. Analysis of time-series temperature data was an effective tool to quantify the flux of water through the streambed with a fine temporal resolution (i.e. daily flux rates) over long periods of time (i.e. annually). Short time-scale temperature records were used to qualitatively assess flux variability with high spatial resolution. Using multiple methods to evaluate streambed dynamics revealed strong linkages between water, heat and solute fluxes.
DE: 1830 Groundwater/surface water interaction
SC: Hydrology [H]
MN: 2007 Fall Meeting