@misc{AngermannJackischAllroggenetal.2017, author = {Angermann, Lisa and Jackisch, Conrad and Allroggen, Niklas and Sprenger, Matthias and Zehe, Erwin and Tronicke, Jens and Weiler, Markus and Blume, Theresa}, title = {Form and function in hillslope hydrology}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {658}, issn = {1866-8372}, doi = {10.25932/publishup-41916}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-419161}, pages = {22}, year = {2017}, abstract = {The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al. (2017).}, language = {en} } @article{AngermannJackischAllroggenetal.2017, author = {Angermann, Lisa and Jackisch, Conrad and Allroggen, Niklas and Sprenger, Matthias and Zehe, Erwin and Tronicke, Jens and Weiler, Markus and Blume, Theresa}, title = {Form and function in hillslope hydrology: characterization of subsurface flow based on response observations}, series = {Hydrology and earth system sciences : HESS}, volume = {21}, journal = {Hydrology and earth system sciences : HESS}, publisher = {Copernicus}, address = {G{\"o}ttingen}, issn = {1027-5606}, doi = {10.5194/hess-21-3727-2017}, pages = {3727 -- 3748}, year = {2017}, abstract = {The phrase form and function was established in architecture and biology and refers to the idea that form and functionality are closely correlated, influence each other, and co-evolve. We suggest transferring this idea to hydrological systems to separate and analyze their two main characteristics: their form, which is equivalent to the spatial structure and static properties, and their function, equivalent to internal responses and hydrological behavior. While this approach is not particularly new to hydrological field research, we want to employ this concept to explicitly pursue the question of what information is most advantageous to understand a hydrological system. We applied this concept to subsurface flow within a hillslope, with a methodological focus on function: we conducted observations during a natural storm event and followed this with a hillslope-scale irrigation experiment. The results are used to infer hydrological processes of the monitored system. Based on these findings, the explanatory power and conclusiveness of the data are discussed. The measurements included basic hydrological monitoring methods, like piezometers, soil moisture, and discharge measurements. These were accompanied by isotope sampling and a novel application of 2-D time-lapse GPR (ground-penetrating radar). The main finding regarding the processes in the hillslope was that preferential flow paths were established quickly, despite unsaturated conditions. These flow paths also caused a detectable signal in the catchment response following a natural rainfall event, showing that these processes are relevant also at the catchment scale. Thus, we conclude that response observations (dynamics and patterns, i.e., indicators of function) were well suited to describing processes at the observational scale. Especially the use of 2-D time-lapse GPR measurements, providing detailed subsurface response patterns, as well as the combination of stream-centered and hillslope-centered approaches, allowed us to link processes and put them in a larger context. Transfer to other scales beyond observational scale and generalizations, however, rely on the knowledge of structures (form) and remain speculative. The complementary approach with a methodological focus on form (i.e., structure exploration) is presented and discussed in the companion paper by Jackisch et al. (2017).}, language = {en} } @article{BloschlZehe2005, author = {Bloschl, G{\"u}nter and Zehe, Erwin}, title = {Invited commentary : on hydrological predictability}, year = {2005}, language = {en} } @misc{BlumeZeheBronstert2009, author = {Blume, Theresa and Zehe, Erwin and Bronstert, Axel}, title = {Use of soil moisture dynamics and patterns at different spatio-temporal scales for the investigation of subsurface flow processes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-44924}, year = {2009}, abstract = {Spatial patterns as well as temporal dynamics of soil moisture have a major influence on runoff generation. The investigation of these dynamics and patterns can thus yield valuable information on hydrological processes, especially in data scarce or previously ungauged catchments. The combination of spatially scarce but temporally high resolution soil moisture profiles with episodic and thus temporally scarce moisture profiles at additional locations provides information on spatial as well as temporal patterns of soil moisture at the hillslope transect scale. This approach is better suited to difficult terrain (dense forest, steep slopes) than geophysical techniques and at the same time less cost-intensive than a high resolution grid of continuously measuring sensors. Rainfall simulation experiments with dye tracers while continuously monitoring soil moisture response allows for visualization of flow processes in the unsaturated zone at these locations. Data was analyzed at different spacio-temporal scales using various graphical methods, such as space-time colour maps (for the event and plot scale) and binary indicator maps (for the long-term and hillslope scale). Annual dynamics of soil moisture and decimeterscale variability were also investigated. The proposed approach proved to be successful in the investigation of flow processes in the unsaturated zone and showed the importance of preferential flow in the Malalcahuello Catchment, a datascarce catchment in the Andes of Southern Chile. Fast response times of stream flow indicate that preferential flow observed at the plot scale might also be of importance at the hillslope or catchment scale. Flow patterns were highly variable in space but persistent in time. The most likely explanation for preferential flow in this catchment is a combination of hydrophobicity, small scale heterogeneity in rainfall due to redistribution in the canopy and strong gradients in unsaturated conductivities leading to self-reinforcing flow paths.}, language = {en} } @article{BolduanZehe2006, author = {Bolduan, Rainer and Zehe, Erwin}, title = {Degradation of isoproturon in earthworm macropores and subsoil matrix : a field study}, issn = {1436-8730}, doi = {10.1002/jpin.200521754}, year = {2006}, abstract = {The objective is to compare the time scale of microbial degradation of the herbicide Isoproturon at the end of earthworm burrows with the time scale of microbial degradation in the surrounding soil matrix. To this end, we developed a method which allows the observation of microbial degradation on Isoproturon in macropores under field conditions. Study area was the well-investigated Weiherbach catchment (Kraichgau, SW Germany). The topsoil of a 12 m(2) large plot parcel was removed, the parcel was covered with a tent and instrumented with TDR and temperature sensors at two depths. After preliminary investigations to optimize application and sampling techniques, the bottom of 55 earthworm burrows, located at a depth of 80-100cm, was inoculated with Isoproturon. Within an interval of 8 d, soil material from the bottom of 5-6 earthworm burrows was taken into the laboratory and analyzed for the Isoproturon concentration for investigation of the degradation kinetics. Furthermore, the degradation of Isoproturon in the soil matrix, that surrounded the macropores at the field plot, was observed in the laboratory. Microbial degradation of Isoproturon at the bottom of the earthworm burrows was with a DT-50-value of 15.6 d almost as fast as in the topsoil. In the soil matrix that closely surrounded the center of the earthworm burrows, no measurable degradation was observed within 30 d. The clearly slower degradation in the soil matrix may be likely explained by a lower microbial activity that was observed in the surrounding soil matrix. The results give evidence that deterministic modeling of the fate of pesticides once transported into heterogeneous subsoils by preferential flow requires an accuracy of a few centimeters in terms of predicting spatial locations: time scales of microbial degradation in the subsoil drop almost one order of magnitude, in case the herbicides dislocates from the bottom of an earthworm burrow a few centimeter into the surrounding soil matrix. If at all, predictions of such an accuracy can only be achieved at locations at sites where the soil hydraulic properties and the macropore system are known at a very high spatial resolution}, language = {en} } @article{BronstertCreutzfeldtGraeffetal.2012, author = {Bronstert, Axel and Creutzfeldt, Benjamin and Gr{\"a}ff, Thomas and Hajnsek, Irena and Heistermann, Maik and Itzerott, Sibylle and Jagdhuber, Thomas and Kneis, David and Lueck, Erika and Reusser, Dominik and Zehe, Erwin}, title = {Potentials and constraints of different types of soil moisture observations for flood simulations in headwater catchments}, series = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards}, volume = {60}, journal = {Natural hazards : journal of the International Society for the Prevention and Mitigation of Natural Hazards}, number = {3}, publisher = {Springer}, address = {New York}, issn = {0921-030X}, doi = {10.1007/s11069-011-9874-9}, pages = {879 -- 914}, year = {2012}, abstract = {Flood generation in mountainous headwater catchments is governed by rainfall intensities, by the spatial distribution of rainfall and by the state of the catchment prior to the rainfall, e. g. by the spatial pattern of the soil moisture, groundwater conditions and possibly snow. The work presented here explores the limits and potentials of measuring soil moisture with different methods and in different scales and their potential use for flood simulation. These measurements were obtained in 2007 and 2008 within a comprehensive multi-scale experiment in the Weisseritz headwater catchment in the Ore-Mountains, Germany. The following technologies have been applied jointly thermogravimetric method, frequency domain reflectometry (FDR) sensors, spatial time domain reflectometry (STDR) cluster, ground-penetrating radar (GPR), airborne polarimetric synthetic aperture radar (polarimetric SAR) and advanced synthetic aperture radar (ASAR) based on the satellite Envisat. We present exemplary soil measurement results, with spatial scales ranging from point scale, via hillslope and field scale, to the catchment scale. Only the spatial TDR cluster was able to record continuous data. The other methods are limited to the date of over-flights (airplane and satellite) or measurement campaigns on the ground. For possible use in flood simulation, the observation of soil moisture at multiple scales has to be combined with suitable hydrological modelling, using the hydrological model WaSiM-ETH. Therefore, several simulation experiments have been conducted in order to test both the usability of the recorded soil moisture data and the suitability of a distributed hydrological model to make use of this information. The measurement results show that airborne-based and satellite-based systems in particular provide information on the near-surface spatial distribution. However, there are still a variety of limitations, such as the need for parallel ground measurements (Envisat ASAR), uncertainties in polarimetric decomposition techniques (polarimetric SAR), very limited information from remote sensing methods about vegetated surfaces and the non-availability of continuous measurements. The model experiments showed the importance of soil moisture as an initial condition for physically based flood modelling. However, the observed moisture data reflect the surface or near-surface soil moisture only. Hence, only saturated overland flow might be related to these data. Other flood generation processes influenced by catchment wetness in the subsurface such as subsurface storm flow or quick groundwater drainage cannot be assessed by these data. One has to acknowledge that, in spite of innovative measuring techniques on all spatial scales, soil moisture data for entire vegetated catchments are still today not operationally available. Therefore, observations of soil moisture should primarily be used to improve the quality of continuous, distributed hydrological catchment models that simulate the spatial distribution of moisture internally. Thus, when and where soil moisture data are available, they should be compared with their simulated equivalents in order to improve the parameter estimates and possibly the structure of the hydrological model.}, language = {en} } @article{EhretZehe2010, author = {Ehret, Uwe and Zehe, Erwin}, title = {Series distance : an intuitive metric for hydrograph comparison}, issn = {1812-2108}, doi = {10.5194/hessd-7-8387-2010}, year = {2010}, abstract = {Applying metrics for hydrograph comparison is a central task in hydrological modelling, used both in model calibration and the evaluation of simulations or forecasts. Motivated by the shortcomings of standard objective metrics such as the Root Mean Square Error or the Mean Peak Time Error and the advantages of visual inspection as a powerful tool for simultaneous, case-specific and multi-criteria (yet subjective) evaluation, we propose a new objective metric termed Series Distance, which is in close accordance with visual evaluation. The Series Distance is an event-based method and consists of three parts, namely a Threat Score which evaluates overall agreement of event occurrence, and the overall distance of matching observed and simulated events with respect to amplitude and timing. The novelty of the latter two is the way in which matching point pairs on the observed and simulated hydrographs are identified, namely by the same relative position in matching segments (rise or recession) of matching events. Thus, amplitude and timing errors are calculated simultaneously but separately, from point pairs that also match visually, considering complete events rather than only individual points (which is for example the case with metrics related to Peak Time Errors). After presenting the Series Distance theory, we discuss its properties and compare it to those of standard metrics and visual inspection, both at the example of simple, artificial hydrographs and an ensemble of realistic forecasts. The results suggest that the Series Distance compares and evaluates hydrographs in a way comparable to visual inspection, but in an objective, reproducible way.}, language = {en} } @article{GraeffZeheReusseretal.2009, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Reusser, Dominik and Lueck, Erika and Schroeder, Boris and Wenk, Gerald and John, Hermann and Bronstert, Axel}, title = {Process identification through rejection of model structures in a mid-mountainous rural catchment : observations of rainfall-runoff response, geophysical conditions and model inter-comparison}, issn = {0885-6087}, doi = {10.1002/Hyp.7171}, year = {2009}, abstract = {The intention of the presented study is to gain a better understanding of the mechanisms that caused the bimodal rainfall-runoff responses which occurred up to the mid-1970s regularly in the Schafertal catchment and vanished after the onset of mining activities. Understanding, this process is a first step to understanding the ongoing hydrological change in this area. It is hypothesized that either subsurface stormflow, or fast displacement of groundwater, could cause the second delayed peak. A top-down analysis of rainfall-runoff data, field observations as well as process modelling are combined within a rejectionistic framework. A statistical analysis is used to test whether different predictors. which characterize the forcing. near surface water content and deeper subsurface store, allow the prediction of the type of rainfall-runoff response. Regression analysis is used with generalized linear models Lis they can deal with non-Gaussian error distributions Lis well its a non-stationary variance. The analysis reveals that the dominant predictors are the pre-event discharge (proxy of state of the groundwater store) and the precipitation amount, In the field campaign, the subsurface at a representative hillslope was investigated by means of electrical resistivity tomography in order to identify possible strata as flow paths for subsurface stormflow. A low resistivity in approximately 4 in depth-either due to a less permeable layer or the groundwater surface-was detected. The former Could serve as a flow path for subsurface stormflow. Finally, the physical-based hydrological model CATFLOW and the groundwater model FEFLOW are compared with respect to their ability to reproduce the bimodal runoff responses. The groundwater model is able to reproduce the observations, although it uses only an abstract representation of the hillslopes. Process model analysis as well Lis statistical analysis strongly suggest that fast displacement of groundwater is the dominant process underlying the bimodal runoff reactions.}, language = {en} } @article{GraeffZeheSchlaegeretal.2010, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Schlaeger, Stefan and Morgner, Markus and Bauer, Andreas and Becker, Rolf and Creutzfeldt, Benjamin and Bronstert, Axel}, title = {A quality assessment of Spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments}, issn = {1027-5606}, doi = {10.5194/hess-14-1007-2010}, year = {2010}, abstract = {Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogeneous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile, but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture, but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16\% were in good agreement with independent measurements.}, language = {en} } @article{GraeffZeheSchlaegeretal.2010, author = {Gr{\"a}ff, Thomas and Zehe, Erwin and Schl{\"a}ger, Stefan and Morgner, Markus and Bauer, Andreas and Becker, Rolf and Creutzfeldt, Benjamin and Bronstert, Axel}, title = {A quality assessment of spatial TDR soil moisture measurements in homogenous and heterogeneous media with laboratory experiments}, issn = {1812-2108}, doi = {10.5194/hessd-7-269-2010}, year = {2010}, abstract = {Investigation of transient soil moisture profiles yields valuable information of near- surface processes. A recently developed reconstruction algorithm based on the telegraph equation allows the inverse estimation of soil moisture profiles along coated, three rod TDR probes. Laboratory experiments were carried out to prove the results of the inversion and to understand the influence of probe rod deformation and solid objects close to the probe in heterogonous media. Differences in rod geometry can lead to serious misinterpretations in the soil moisture profile but have small influence on the average soil moisture along the probe. Solids in the integration volume have almost no effect on average soil moisture but result in locally slightly decreased moisture values. Inverted profiles obtained in a loamy soil with a clay content of about 16\% were in good agreement with independent measurements.}, language = {en} }