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- W2890540295 abstract "Stream water and groundwater areimportant fresh water resources but their water quality isdeteriorated by harmful solutes introduced by human activities. Theinterface between stream water and the subsurface water is animportant zone for retention, transformation and attenuation ofthese solutes. Streambed structures enhance these processes byincreased water and solute exchange across this interface, denotedas hyporheic exchange. This thesis investigates the influence ofhydrological and morphological factors on hyporheic water andsolute exchange as well as redox-reactions in fluvial streambedstructures on the intermediate scale (10–30m). For this purpose, athree-dimensional numerical modeling approach for coupling streamwater flow with porous media flow is used. Multiple steady statestream water flow scenarios over different generic pool-rifflemorphologies and a natural in-stream gravel bar are simulated by acomputational fluid dynamics code that provides the hydraulic headdistribution at the streambed. These heads are subsequently used asthe top boundary condition of a reactive transport groundwatermodel of the subsurface beneath the streambed. Ambient groundwaterthat naturally interacts with the stream water is considered inscenarios of different magnitudes of downwelling stream water(losing case) and upwelling groundwater (gaining case). Also, theneutral case, where stream stage and groundwater levels arebalanced is considered. Transport of oxygen, nitrate and dissolvedorganic carbon and their reaction by aerobic respiration anddenitrification are modeled. The results show that stream stageand discharge primarily induce hyporheic exchange flux and solutetransport with implications for specific residence times andreactions at both the fully and partially submerged structures.Gaining and losing conditions significantly diminish the extent ofthe hyporheic zone, the water exchange flux, and shorten residencetimes for both the fully and partially submerged structures. Withincreasing magnitude of gaining or losing conditions, these metricsexponentially decrease. Stream water solutes are transportedmainly advectively into the hyporheic zone and hence their influxcorresponds directly to the infiltrating water flux. Aerobicrespiration takes place in the shallow streambed sediments,coinciding to large parts with the extent of the hyporheic exchangeflow. Denitrification occurs mainly as a “reactive fringe”surrounding the aerobic zone, where oxygen concentration is low andstill a sufficient amount of stream water carbon source isavailable. The solute consumption rates and the efficiency of theaerobic and anaerobic reactions depend primarily on the availablereactive areas and the residence times, which are both controlledby the interplay between hydraulic head distribution at thestreambed and the gradients between stream stage and ambientgroundwater. Highest solute consumption rates can be expected underneutral conditions, where highest solute flux, longest residencetimes and…" @default.
- W2890540295 created "2018-09-27" @default.
- W2890540295 creator A5023068836 @default.
- W2890540295 date "2015-01-01" @default.
- W2890540295 modified "2023-09-24" @default.
- W2890540295 title "Flow and reactivetransport modeling at the stream-groundwater interface" @default.
- W2890540295 hasPublicationYear "2015" @default.
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