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  • 1
    In: Hydrological Processes, 01 January 2017, Vol.31(1), pp.15-19
    Description: Preferential flow is of high relevance for runoff generation, transport of chemicals and nutrients, and the transit time distribution of water in the soil or watershed. However, preferential flow effects are generally ignored in lumped hydrological models. And even most physically‐based models ignore macropores and preferential flow features at the soil and hillslope scale. Keith Beven was never satisfied with this situation and he tried again and again to convince the scientific community to focus their research on the complex topic of macropore and preferential flow. Although he recognized how difficult it is to correctly include preferential flow in hydrological models, he made substantial progress defining and describing macropore flow and showing its relevance, developing models to simulate preferential flow, and in particular, the interaction between macropores and the soil matrix. In this short commentary, I reflect on these achievements and outline a vision for research in preferential flow experiments and modeling.
    Keywords: Infiltration ; Macropore Flow ; Preferential Flow ; Runoff Generation
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 2
    Language: English
    In: Journal of Hydrology, 2011, Vol.396(3), pp.277-291
    Description: ► Specification of spatially distributed lateral fluxes affects solute transport parameter estimates. ► Information contained on the breakthrough curve alone is insufficient to select the appropriate model structure. ► Implementation of , the lateral ouflow, in OTIS leads to solute mass to groundwater. ► The absence of implementation of in OTIS promotes the storage of solute mass in the transient storage zone. Interactions between mobile stream water and transient storage zones have been the subject of careful attention for decades. However, few studies have considered explicitly the influence of water exchange between the channel and neighbouring hydrological units when modelling transient storage processes, especially the lateral inflow coming from hillslope contributions and outflow to a deep aquifer or to hyporheic flow paths extending beyond the study reach. The objective of this study was to explore the influence of different conceptualizations of these hydrologic exchanges on the estimation of transient storage parameters. Slug injections of sodium chloride (NaCl) were carried out in eight contiguous reaches in the Cotton Creek Experimental Watershed (CCEW), located in south-east British Columbia. Resulting breakthrough curves were subsequently analysed using a Transient Storage Model (TSM) in an inverse modelling framework. We estimated solute transport parameters using three distinct, hypothetical spatial patterns of lateral inflow and outflow, all based on variations of the same five-parameter model structure. We compared optimized parameter values to those resulting from a distinct four-parameter model structure meant to represent the standard application of the TSM, in which only lateral inflow was implemented for net gaining reaches or only lateral outflow for net losing reaches. In the five-parameter model, solute mass was stored predominantly in the transient storage zone and slowly released back to the stream. Conversely, solute mass was predominantly removed from the stream via flow losses in the four-parameter model structure. This led to contrasting estimates of solute transport parameters and subsequent interpretation of solute transport dynamics. Differences in parameter estimates across variations of the five-parameter model structure were small yet statistically significant, except for the transient storage exchange rate coefficient , for which unique determination was problematic. We also based our analysis on , the fraction of median transport time due to transient storage. Differences across configurations in estimates were consistent but small when compared to the variability of among reaches. Optimized parameter values were influenced dominantly by the model structure (four versus five parameters) and then by the conceptualization of spatial arrangement of lateral fluxes along the reach for a set model structure. When boundary conditions are poorly defined, the information contained in the stream tracer breakthrough curve is insufficient to identify a single, unambiguous model structure representing solute transport simulations. Investigating lateral fluxes prior to conducting a study on transient storage processes is necessary, as assuming a certain spatial organization of these fluxes might set ill-defined bases for inter-reach comparisons. Given the difficulty in quantifying the spatial patterns and magnitudes of lateral inputs and outputs, we recommend small-scale laboratory tracer experiments with well-defined and variable boundary conditions as a complement to field studies to provide new insights into stream solute dynamics.
    Keywords: Transient Storage ; Flow Loss ; Flow Gain ; Otis ; Uncertainty ; Model Structure ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Journal of Hydrology, 2006, Vol.319(1), pp.339-356
    Description: The delivery mechanisms of labile nutrients (e.g. NO , DON and DOC) to streams are poorly understood. Recent work has quantified the relationship between storm DOC dynamics and the connectedness of catchment units and between pre-storm wetness and transient groundwater NO flushing potential. While several studies have shown N and C flushing during storm events as the important mechanism in the export of DOC and DON in small catchments, the actual mechanisms at the hillslope scale have remained equivocal. The difficulty in isolating cause and effect in field studies is made difficult due to the spatial variability of soil properties, the limited ability to detect flow pathways within the soil, and other unknowns. Some hillslopes show preferential flow behavior that may allow transmission of hillslope runoff and labile nutrients with little matrix interaction; others do not. Thus, field studies are only partially useful in equating C and N sources with water flow and transport. This paper presents a new approach to the study of hydrological controls on labile nutrient flushing at the hillslope scale. We present virtual experiments that focus on quantifying the first-order controls on flow pathways and nutrient transport in hillslopes. We define virtual experiments as numerical experiments with a model driven by collective field intelligence. We present a new distributed model that describes the lateral saturated and vertical unsaturated water flow from hypothetical finite nutrient sources in the upper soil horizons. We describe how depth distributions of transmissivity and drainable porosity, soil depth variability, as well as mass exchange between the saturated and unsaturated zone influence the mobilization, flushing and release of labile nutrients at the hillslope scale. We argue that this virtual experiment approach may provide a well-founded basis for defining the first-order controls and linkages between hydrology and biogeochemistry at the hillslope scale and perhaps form a basis for predicting flushing and transport of labile nutrients from upland to riparian zones.
    Keywords: Virtual Experiments ; Hillslope Hydrology ; Nutrients ; Mobilization ; Flushing ; Runoff Generation ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 4
    In: Hydrological Processes, 15 February 2014, Vol.28(4), pp.1916-1930
    Description: Monitoring runoff generation processes in the field is a prerequisite for developing conceptual hydrological models and theories. At the same time, our perception of hydrological processes strongly depends on the spatial and temporal scale of observation. Therefore, the aim of this study is to investigate interactions between runoff generation processes of different spatial scales (plot scale, hillslope scale, and headwater scale). Different runoff generation processes of three hillslopes with similar topography, geology and soil properties, but differences in vegetation cover (grassland, coniferous forest, and mixed forest) within a small v‐shaped headwater were measured: water table dynamics in wells with high spatial and temporal resolution, subsurface flow (SSF) of three 10 m wide trenches at the bottom of the hillslopes subdivided into two trench sections each, overland flow at the plot scale, and catchment runoff. Bachmair . ([Bachmair S, 2012]) found a high spatial variability of water table dynamics at the plot scale. In this study, we investigate the representativity of SSF observations at the plot scale the hillslope scale and vice versa, and the linkage between hillslope dynamics (SSF and overland flow) and streamflow. Distinct differences in total SSF within each 10 m wide trench confirm the high spatial variability of the water table dynamics. The representativity of plot scale observations for hillslope scale SSF strongly depends on whether or not wells capture spatially variable flowpaths. At the grassland hillslope, subsurface flowpaths are not captured by our relatively densely spaced wells (3 m), despite a similar trench flow response to the coniferous forest hillslope. Regarding the linkage between hillslope dynamics and catchment runoff, we found an intermediate to high correlation between streamflow and hillslope hydrological dynamics (trench flow and overland flow), which highlights the importance of hillslope processes in this small watershed. Although the total contribution of SSF to total event catchment runoff is rather small, the contribution during peak flow is moderate to substantial. Additionally, there is process synchronicity between spatially discontiguous measurement points across scales, potentially indicating subsurface flowpath connectivity. Our findings stress the need for (i) a combination of observations at different spatial scales, and (ii) a consideration of the high spatial variability of SSF at the plot and hillslope scale when designing monitoring networks and assessing hydrological connectivity. Copyright © 2013 John Wiley & Sons, Ltd.
    Keywords: Subsurface Flow ; Preferential Flow ; Hillslope Hydrology ; Scale Effects ; Hydrological Connectivity ; Monitoring Networks
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 5
    In: Canadian Journal of Forest Research (Revue canadienne de recherche forestière), 2010, Vol.40(4), pp.812-821
    Description: The current mountain pine beetle infestation in British Columbias lodgepole pine forests has raised concerns about potential impacts on water resources. Changes in forest structure resulting from defoliation, windthrow, and salvage harvesting may increase snow accumulation and ablation (i.e., spring runoff and flooding risk) below the forest canopy because of reduced snow interception and higher levels of radiation reaching the surface. Quantifying these effects requires a better understanding of the link between forest structure and snow processes. Light detection and ranging (lidar) is an innovative technology capable of estimating forest structure metrics in a detailed, three-dimensional approach not easily obtained from manual measurements. While a number of previous studies have shown that increased snow accumulation and ablation occur as forest cover decreases, the potential improvement of these relationships based on lidar metrics has not been quantified. We investigated the correlation between lidar-derived and ground-based traditional canopy metrics with snow accumulation and ablation indicators, demonstrating that a lidar-derived forest cover parameter was the strongest predictor of peak snow accumulation ( r 2 = 0.70, p 〈 0.001) and maximum snow ablation rate ( r 2 = 0.59, p 〈 0.01). Improving our ability to quantify changes in forest structure in extensive areas will assist in developing more robust models of watershed processes.
    Description: Linfestation actuelle du dendroctone du pin ponderosa dans les forts de pin tordu de la Colombie-Britannique a suscit des inquitudes quant aux impacts potentiels sur les ressources hydriques. Les changements dans la structure de la fort causs par la dfoliation, les chablis et les coupes de rcupration pourraient augmenter laccumulation de neige et lablation nivale (c.--d. le ruissellement printanier et le risque dinondation) sous le couvert forestier en rduisant linterception et en augmentant le rayonnement au sol. La quantification de ces effets exige une meilleure comprhension du lien entre la structure de la fort et les processus nivaux. La dtection et tlmtrie par ondes lumineuses (lidar) est une technologie innovatrice capable destimer les mtriques de la structure de la fort avec une approche tridimensionnelle dtaille, difficile obtenir laide de mesures prises manuellement. Bien que plusieurs tudes prcdentes aient montr que laccumulation de neige et lablation nivale augmentent mesure que le couvert forestier diminue, lamlioration potentielle de ces relations au moyen de donnes lidar na pas t quantifie. Nous avons tudi la corrlation entre les mesures du couvert drives du lidar et les mesures traditionnelles prises au sol avec des indicateurs daccumulation de neige et dablation nivale. Nous avons dmontr quun paramtre du couvert forestier driv du lidar est le meilleure prdicteur de laccumulation maximale de neige ( r 2 = 0,70, p 〈 0,001) et du taux maximum dablation nivale ( r 2 = 0,59, p 〈 0,01). Lamlioration de notre capacit quantifier les changements dans la structure de la fort sur de vastes tendues contribuera dvelopper des modles plus robustes des processus dans les bassins versants.
    Keywords: Forest Management -- Methods ; Tree Crops -- Distribution;
    ISSN: 0045-5067
    E-ISSN: 1208-6037
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  • 6
    Language: English
    In: Journal of Hydrology, 27 November 2014, Vol.519, pp.340-352
    Description: Assessing temporal variations in soil water flow is important, especially at the hillslope scale, to identify mechanisms of runoff and flood generation and pathways for nutrients and pollutants in soils. While surface processes are well considered and parameterized, the assessment of subsurface processes at the hillslope scale is still challenging since measurement of hydrological pathways is connected to high efforts in time, money and personnel work. The latter might not even be possible in alpine environments with harsh winter processes. Soil water stable isotope profiles may offer a time-integrating fingerprint of subsurface water pathways. In this study, we investigated the suitability of soil water stable isotope (δ O) depth profiles to identify water flow paths along two transects of steep subalpine hillslopes in the Swiss Alps. We applied a one-dimensional advection–dispersion model using δ O values of precipitation (ranging from −24.7 to −2.9‰) as input data to simulate the δ O profiles of soil water. The variability of δ O values with depth within each soil profile and a comparison of the simulated and measured δ O profiles were used to infer information about subsurface hydrological pathways. The temporal pattern of δ O in precipitation was found in several profiles, ranging from −14.5 to −4.0‰. This suggests that vertical percolation plays an important role even at slope angles of up to 46°. Lateral subsurface flow and/or mixing of soil water at lower slope angles might occur in deeper soil layers and at sites near a small stream. The difference between several observed and simulated δ O profiles revealed spatially highly variable infiltration patterns during the snowmelt periods: The δ O value of snow (−17.7 ± 1.9‰) was absent in several measured δ O profiles but present in the respective simulated δ O profiles. This indicated overland flow and/or preferential flow through the soil profile during the melt period. The applied methods proved to be a fast and promising tool to obtain time-integrated information on soil water flow paths at the hillslope scale in steep subalpine slopes.
    Keywords: Stable Isotopes ; Soil Water ; Steep Hillslopes ; Modeling ; Water Pathways ; Snowmelt ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 7
    Language: English
    In: Hydrological Processes, August 15, 2015, Vol.29(17), p.3649(16)
    Description: To purchase or authenticate to the full-text of this article, please visit this link: http://onlinelibrary.wiley.com/doi/10.1002/hyp.10460/abstract Byline: Jakob Garvelmann, Stefan Pohl, Markus Weiler Keywords: rain-on-snow; runoff generation; spatio-temporal variability; snowmelt; catchment hydrology; flood Abstract A network of 30 standalone snow monitoring stations was used to investigate the snow cover distribution, snowmelt dynamics, and runoff generation during two rain-on-snow (ROS) events in a 40 km.sub.2 montane catchment in the Black Forest region of southwestern Germany. A multiple linear regression analysis using elevation, aspect, and land cover as predictors for the snow water equivalent (SWE) distribution within the catchment was applied on an hourly basis for two significant ROS flood events that occurred in December 2012. The available snowmelt water, liquid precipitation, as well as the total retention storage of the snow cover were considered in order to estimate the amount of water potentially available for the runoff generation. The study provides a spatially and temporally distributed picture of how the two observed ROS floods developed in the catchment. It became evident that the retention capacity of the snow cover is a crucial mechanism during ROS. It took several hours before water was released from the snowpack during the first ROS event, while retention storage was exceeded within 1h from the start of the second event. Elevation was the most important terrain feature. South-facing terrain contributed more water for runoff than north-facing slopes, and only slightly more runoff was generated at open compared to forested areas. The results highlight the importance of snowmelt together with liquid precipitation for the generation of flood runoff during ROS and the large temporal and spatial variability of the relevant processes. Copyright [c] 2015 John Wiley & Sons, Ltd.
    Keywords: Runoff – Analysis ; Hydrology – Analysis
    ISSN: 0885-6087
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Environmental Earth Sciences, 2012, Vol.65(8), pp.2377-2389
    Description: For water management purposes, information about an entire aquifer system is generally more important than information about a specific spring. Since a karstic aquifer system might drain to several outlets, conclusions derived from a single spring can be misleading for characterization and modeling. In this study we apply a conceptual model to an Alpine dolomite karst system in Austria. The particular challenge was that several small springs with strongly varying hydrological behavior and diffuse flow into surrounding streams drain this system. Instead of applying the model to a single spring, it was calibrated simultaneously to several observations within the system aiming to identify the karst system’s intrinsic hydrodynamic parameters. Parameter identification is supported by modeling the transport of water isotopes (δ 18 O). The parameters were transferred to the whole system with a simple upscaling procedure and a sensitivity analysis was performed to unfold influence of isotopic information on parameter sensitivity and simulation uncertainty. The results show that it is possible to identify system intrinsic parameters. But the sensitivity analysis revealed that some are hardly identifiable. Only by considering uncertainty reasonable predictions can be provided for the whole system. Including isotopic information increases the sensitivity of some intrinsic parameters, but it goes along with a sensitivity decrease for others. However, a possible reduction of prediction uncertainty by isotopic information is compensated by deficiencies in the transport modeling routines.
    Keywords: Karst aquifer ; Karst modeling ; Water isotopes ; Solute transport modeling ; Upscaling ; Rainfall-runoff modeling
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 9
    In: Ecohydrology, November 2012, Vol.5(6), pp.721-732
    Description: Changes of the land surface affect the water balance components over seasonal, annual and decadal time scales. This study explored the role of vegetation cover transitions on evapotranspiration in forested watersheds of the North American West. We applied empirical time‐recovery functions describing the impact of forest removal and subsequent regrowth on actual evapotranspiration () or runoff. A generalized function () was adapted to the North American West and tested using three different datasets of observed or estimated in forest chronosequences: from flux towers equipped with eddy covariance sensors, estimated from the water balance in experimental paired watersheds and in a set of gauged watersheds with considerable forest cover history dating back to the 18th century. from the first two datasets showed a behaviour similar to the K‐curve, although the timing and the magnitude differed substantially. To reconstruct long‐term changes in for the gauged watersheds, we applied a transfer function approach linking the K‐curve and the reconstructed forest cover history at the watershed scale. In several watersheds, correlation coefficients between the reconstructed changes and the annual water balances suggest that changes in time were driven by the land cover transitions. In watersheds with low correlations, disturbance activities peaked before the 20th century, and the effects of vegetation have phased out in the period of streamflow observations. The findings of this paper suggest that trends in the observed water balance in forested watersheds can be associated to land cover disturbances well before the start of hydro‐climatic observations. Copyright © 2011 John Wiley & Sons, Ltd.
    Keywords: Forest Disturbance ; Recovery ; Evapotranspiration ; Stand Age ; North American West ; Water Balance ; Forest Cover History ; Eddy Covariance Fluxes
    ISSN: 1936-0584
    E-ISSN: 1936-0592
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  • 10
    In: Hydrological Processes, 15 August 2015, Vol.29(17), pp.3649-3664
    Description: A network of 30 standalone snow monitoring stations was used to investigate the snow cover distribution, snowmelt dynamics, and runoff generation during two rain‐on‐snow (ROS) events in a 40 km montane catchment in the Black Forest region of southwestern Germany. A multiple linear regression analysis using elevation, aspect, and land cover as predictors for the snow water equivalent (SWE) distribution within the catchment was applied on an hourly basis for two significant ROS flood events that occurred in December 2012. The available snowmelt water, liquid precipitation, as well as the total retention storage of the snow cover were considered in order to estimate the amount of water potentially available for the runoff generation. The study provides a spatially and temporally distributed picture of how the two observed ROS floods developed in the catchment. It became evident that the retention capacity of the snow cover is a crucial mechanism during ROS. It took several hours before water was released from the snowpack during the first ROS event, while retention storage was exceeded within 1 h from the start of the second event. Elevation was the most important terrain feature. South‐facing terrain contributed more water for runoff than north‐facing slopes, and only slightly more runoff was generated at open compared to forested areas. The results highlight the importance of snowmelt together with liquid precipitation for the generation of flood runoff during ROS and the large temporal and spatial variability of the relevant processes. Copyright © 2015 John Wiley & Sons, Ltd.
    Keywords: Rain‐On‐Snow ; Runoff Generation ; Spatio‐Temporal Variability ; Snowmelt ; Catchment Hydrology ; Flood
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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