<p>In the recent decades, therehave been frequent conflicts between groundwater waterresources and environmentally hazardous activities. Newmethodologies for aiding decision-making in groundwater impactassessment and protection areneeded and in which issues ofincreased awareness, better understanding of the groundwaterresources processes, and validation of predictive mathematicalmodels are addressed.</p><p>A framework fordecision–aid, based on predictive simulations that a)predicts the environmental impacts b) provides the totaleconomical value c) visualises the impacts and the groundwaterproperties and d) describes the uncertainties in the results isproposed herein. The framework can be applied in environmentalimpact assessments, strategic environmental assessments andprotection and management of water resources. The results ofthe model are used as feedback for determining new scenarios,depending on the required uncertainties, and if the plannedactivity is sustainable, and/or fulfils the legislative andpolicy measures. This framework is applied to a particular casestudy, Nybroåsen, in the south-eastern part of Sweden,where the highway E22 is constructed through the importantglaciofluvial esker aquifer, passing the protection zone of thewater supply for the Kalmar municipality.</p><p>The impacts from the new highwayand the existing road have been predicted by two-dimensionalphysically based time-variant flow and solute groundwatermodelling. The results, breakthrough curves of contaminantconcentration in wells and maps of concentration distributions,as well as travel times, flow paths, and capture zones forwells determined by particle tracking have been presented.</p><p>The constructed model of theNybroåsen study area was calibrated by comparing observedand simulated groundwater levels for 15 observation wells forten years of measurements. The model has been evaluated bothgraphically and numerically and the calibration target wasfulfilled for 13 of the 15 observation wells. The model workincludes investigations of the catchment information, a waterbalance study, simulation of the groundwater recharge,consideration of the unsaturated zone by a numerical columnsimulation, and sensitivity analysis.</p><p>From the sensitivity analysis ofthe flow and transport parameters, it has been shown that theuncertainties are mainly due to the hydraulic conductivity.Comparison of the derived conductivity from the steady-stateautomatic calibration and the time-variant calibration showedthat there are major differences in the derived parameters,which illustrates the importance of a time dependentcalibration over both wet and dry periods and in more than onepoint in the area of interest of the model predictions.</p><p>In addition, a multi-criteriadecision analysis has been carried out for four roadalternatives (including the new highway E22) and the existingroad in the case study concerned. The multi-criteria decisionaid is applied as an illustration of how it can be used in thestudy area to identify a) interest groups of actors and theirconcerns b) ranking of alternative road scenarios according toactors’preferences and c) coalition groups of actors<i>i.e.</i>groups that have similar views with regard to theroad alternatives.</p><p><b>Keywords:</b>Physically-based groundwater modelling,contamination, flow and solute transport, glaciofluvialdeposits, Nybroåsen, Sweden, and multi-criteriadecision-aid.</p>

In the recent decades, therehave been frequent conflicts between groundwater waterresources and environmentally hazardous activities. Newmethodologies for aiding decision-making in groundwater impactassessment and protection areneeded and in which issues ofincreased awareness, better understanding of the groundwaterresources processes, and validation of predictive mathematicalmodels are addressed. A framework fordecision–aid, based on predictive simulations that a)predicts the environmental impacts b) provides the totaleconomical value c) visualises the impacts and the groundwaterproperties and d) describes the uncertainties in the results isproposed herein. The framework can be applied in environmentalimpact assessments, strategic environmental assessments andprotection and management of water resources. The results ofthe model are used as feedback for determining new scenarios,depending on the required uncertainties, and if the plannedactivity is sustainable, and/or fulfils the legislative andpolicy measures. This framework is applied to a particular casestudy, Nybroåsen, in the south-eastern part of Sweden,where the highway E22 is constructed through the importantglaciofluvial esker aquifer, passing the protection zone of thewater supply for the Kalmar municipality. The impacts from the new highwayand the existing road have been predicted by two-dimensionalphysically based time-variant flow and solute groundwatermodelling. The results, breakthrough curves of contaminantconcentration in wells and maps of concentration distributions,as well as travel times, flow paths, and capture zones forwells determined by particle tracking have been presented. The constructed model of theNybroåsen study area was calibrated by comparing observedand simulated groundwater levels for 15 observation wells forten years of measurements. The model has been evaluated bothgraphically and numerically and the calibration target wasfulfilled for 13 of the 15 observation wells. The model workincludes investigations of the catchment information, a waterbalance study, simulation of the groundwater recharge,consideration of the unsaturated zone by a numerical columnsimulation, and sensitivity analysis. From the sensitivity analysis ofthe flow and transport parameters, it has been shown that theuncertainties are mainly due to the hydraulic conductivity.Comparison of the derived conductivity from the steady-stateautomatic calibration and the time-variant calibration showedthat there are major differences in the derived parameters,which illustrates the importance of a time dependentcalibration over both wet and dry periods and in more than onepoint in the area of interest of the model predictions. In addition, a multi-criteriadecision analysis has been carried out for four roadalternatives (including the new highway E22) and the existingroad in the case study concerned. The multi-criteria decisionaid is applied as an illustration of how it can be used in thestudy area to identify a) interest groups of actors and theirconcerns b) ranking of alternative road scenarios according toactors’preferences and c) coalition groups of actorsi.e.groups that have similar views with regard to theroad alternatives. <b>Keywords:</b>Physically-based groundwater modelling,contamination, flow and solute transport, glaciofluvialdeposits, Nybroåsen, Sweden, and multi-criteriadecision-aid. / NR 20140805

The docotoral thesis titled 'Modeling the effects of Transient Stream Flow on Solute Dynamics in Stream Banks and Intra-meander Zones' investigates flow and solute dynamcis across surface water-groundwater interface under dynamic flow conditons through numerical simulations. The abstract of the thesis is as follows: Waters from various sources meet at the interface between streams and groundwater. Due to their different origins, these waters often have contrasting chemical signatures and therefore mixing of water at the interface may lead to significant changes in both surface and subsurface water quality. The riparian zone adjacent to the stream serves as transition region between groundwater and stream water, where complex water and solute mixing and transport processes occur. Predicting the direction and the magnitude of solute exchanges and the extent of transformations within the riparian zone is challenging due to the varying hydrologic and chemical conditions as well as heterogeneous morphological features which result in complex, three-dimensional flow patterns. The direction of water flow and solute transport in the riparian zone typically varies over time as a result of fluctuating stream water and groundwater levels. Particularly, increasing groundwater levels can mobilize solutes from the unsaturated zone which can be subsequently transported into the stream. Such complex, spatially and temporally varying processes are hard to capture with field observations alone and therefore modeling approaches are required to predict the system behavior as well as to understand the role of individual factors. In this thesis, we investigate the inter-connectivity of streamthe s and adjacent riparia zones in the context of water and solute exchanges both laterally for bank storage and longitudinally for hyporheic flow through meander bends. Using numerical modeling, the transient effect of stream flow events on solute transport and transformation within the initially unsaturated part of stream banks and meander bends have been simulated using a systematic set of hydrological, chemical and morphological scenarios. A two dimensional variably saturated media groundwater modeling set up was used to explore solute dynamics during bank flows. We simulated exchanges between stream and adjacent riparian zone driven by stream stage fluctuations during stream discharge events. To elucidate the effect of magnitude and duration of discharge events, we developed a number of single discharge event scenarios with systematically varying peak heights and event duration. The dominant solute layer was represented by applying high solute concentration in upper unsaturated riparian zone profile. Simulated results show that bank flows generated by high stream flow events can trigger solute mobilization in near stream riparian soils and subsequently export significant amounts of solutes into the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased duration significantly enhance solute export, however, peak height is found to be the dominant control for overall lateral mass export. The mobilized solutes are transported towards the stream in two stages (1) by return flow of stream water that was stored in the riparian zone during the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in a theoretically long tailing of bank outflows and solute mass outfluxes. Our bank flow simulations demonstrate that strong stream discharge events are likely to mobilize and export significant quantity of solutes from near stream riparian zones into the stream. Furthermore, the impact of short-term stream discharge variations on solute exchange may sustain for long times after the flow event. Meanders are prominent morphological features of stream systems which exhibit unique hydrodynamics. The water surface elevation difference across the inner bank of a meander induces lateral hyporheic exchange flow through the intrameander region, leading to solute transport and reactions within intra-meander region. We examine the impact of different meander geometries on the intra-meander hyporheic flow field and solute mobilization under both steady-state and transient flow conditions. In order to explore the impact of meander morphology on intrameander flow, a number of theoretical meander shape scenarios, representing various meander evolution stages, ranging from a typical initial to advanced stage (near cut off ) meander were developed. Three dimensional steady-state numerical groundwater flow simulations including the unsaturated zone were performed for the intra-meander region for all meander scenarios. The meandering stream was implemented in the model by adjusting the top layers of the modeling domain to the streambed elevation. Residence times for the intra-meander region were computed by advective particle tracking across the inner bank of meander. Selected steady state cases were extended to transient flow simulations to evaluate the impact of stream discharge events on the temporal behavior of the water exchange and solute transport in the intra-meander region. Transient hydraulic heads obtained from the surface water model were applied as transient head boundary conditions to the streambed cells of the groundwater model. Similar to the bank storage case, a high concentration of solute (carbon source) representing the dominant solute layer in the riparian profile was added in the unsaturated zone to evaluate the effect of stream flow event on mobilization and transport from the unsaturated part of intrameander region. Additionally, potential chemical reactions of aerobic respiration by the entry of oxygen rich surface water into subsurface as well denitrification due to stream and groundwater borne nitrates were also simulated. The results indicate that intra-meander mean residence times ranging from 18 to 61 days are influenced by meander geometry, as well as the size of the intra-meander area. We found that, intra-meander hydraulic gradient is the major control of RTs. In general, larger intra-meander areas lead to longer flow paths and higher mean intra-meander residence times (MRTs), whereas increased meander sinuosity results in shorter MRTs. The vertical extent of hyporheic flow paths generally decreases with increasing sinuosity. Transient modeling of hyporheic flow through meanders reveals that large stream flow events mobilize solutes from the unsaturated portion of intra-meander region leading to consequent transport into the stream via hyporheic flow. Advective solute transport dominates during the flow event; however significant amount of carbon is also consumed by aerobic respiration and denitrification. These reactions continue after the flow events depending upon the availability of carbon source. The thesis demonstrates that bank flows and intra-meander hyporheic exchange flows trigger solute mobilization from the dominant solute source layers in the RZ. Stream flow events driven water table fluctuations in the stream bank and in the intra-meander region transport substantial amount of solutes from the unsaturated RZ into the stream and therefore have significant potential to alter stream water quality.:Declaration Abstract Zusammenfassung 1 General Introduction 1.1 Background and Motivation 1.2 Hydrology and Riparian zones 1.2.1 Transport processes driven by fluctuation in riparian water table depth 1.2.1.1 Upland control 1.2.1.2 Stream control 1.2.2 Biochemical Transformations within the Riparian Zone 1.3 Types and scales of stream-riparian exchange 1.3.1 Hyporheic Exchange 1.3.1.1 Small Scale Vertical HEF 1.3.1.2 Large Scale lateral HEF 1.3.2 Bank Storage 1.4 Methods for estimation of GW-SW exchanges 1.4.1 Field Methods 1.4.1.1 Direct measurement of water flux 1.4.1.2 Tracer based Methods 1.4.2 Modeling Methods 1.4.2.1 Transient storage models 1.4.2.2 Physically based models 1.5 Research gaps and need 1.6 Objectives of the research 1.7 Thesis Outline 2 Flow and Transport Dynamics during Bank Flows 2.1 Introduction 2.2 Methods 2.2.1 Concept and modeling setup 2.2.2 Numerical Model 2.2.3 Stream discharge events 2.2.4 Model results evaluation 2.3 Results and discussion 2.3.1 Response of water and solute exchange to stream discharge events 2.3.1.1 Water exchange time scales 2.3.1.2 Stream water solute concentration 2.3.2 Solute mobilization within the riparian zone 2.3.3 Influence of peak height and event duration on solute mass export towards the stream 2.3.4 Effects of event hydrograph shape on stream water solute concentration 2.3.5 Model limitations and future studies 2.4 Summary and Conclusions Appendix 2 3 Flow and Transport Dynamics within Intra-Meander Zone 3.1 Introduction 3.2 Methods 3.2.1 Meander Shape Scenarios 3.2.2 Surface Water Simulations 3.2.3 3D Groundwater Flow Simulations with Modeling code MIN3P 3.2.3.1 Steady Flow Simulations 3.2.3.2 Stream flow event and Solute Mobilization Set-up 3.2.4 Reactive Transport 3.3 Results and Discussion 3.3.1 Groundwater heads and flow paths in the saturated intrameander zone 3.3.1.1 Groundwater heads 3.3.1.2 Flow paths and isochrones 3.3.1.3 Vertical extent of flow paths 3.3.2 Intra-Meander Residence Time Distribution 3.3.3 Factors affecting intra-meander flow and residence times 3.3.3.1 intra-meander hydraulic gradient 3.3.3.2 Maximum penetration depth 3.3.3.3 Meander sinuosity 3.3.3.4 intra-meander area (A) 3.3.4 Influence of Discharge Event on intra-meander Flow and Solute Transport 3.3.4.1 Spatial distribution of groundwater head and solute concentration 3.3.4.2 Time scales of intra-meander groundwater heads and solute transport 3.3.4.3 Solute export during stream discharge event 3.3.5 Intra-meander reactive transport during stream discharge event 3.3.5.1 Impact of stream discharge on aerobic respiration and denitrification 3.3.5.2 DOC mass removal during stream discharge event 3.4 Summary and Conclusions Appendix 3 4 General Summary and Conclusions 4.1 Summary 4.2 Conclusions 4.2.1 Flow and Transport Dynamics in Near Stream Riparian Zone (Bank Flows) 4.2.2 Flow and Transport Dynamics within Intra-Meander Zone 4.3 Model Limitations and Future Studies Bibliography Acknowledgement