HR: 0800h
AN: H41F-0343    [Abstracts]
TI: Quantifying hyporheic exchange in streams and rivers - Experimental limitations and practical relevance
AU: * Worman, A
EM: anders.worman@bt.slu.se
AF: Anders Worman, Dept of Biometry and Engineering / SLU, Uppsala, 75007 Sweden
AB: Mixing of water and solute elements between streams and groundwater is controlled by various mechanisms such as in-stream mixing, flooding, and surface water-groundwater interaction. Major problems are to theoretically describe the hyporheic exchange mechanism and to measure it from tracer experiments. The surface water-groundwater exchange can be caused by pumping due to bed-forms, stream curvature, stream-slope variations and landscape topography on various scales. This implies severe difficulties to discriminate between effects of various exchange mechanisms on breakthrough curves from tracer experiments and to generalise results to conditions other than those under which measurements were performed. This work describes how the tail of the breakthrough curves from tracer tests can be used to interpret certain types of hyporheic exchange and the limitations with respect to generalisation. Experimental data from both small streams are show that the pumping mechanism may often dominate the exchange. A field study of the Phosphorus transport due to sewage effluents from a large number of individual households into a stream network indicates the tremendous impact of the hyporheic pumping exchange on the overall watershed response. Especially for sorbing solutes, like phosphorus, the filtration in the subsurface effectively retard the transport. The difficulty in exact measurements of all mechanisms leading to surface water-groundwater exchange and filtration implies a great source of uncertainty in watershed modelling. Potential model biases due to experimental errors are analysed in the study.
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting