In a pilot study the bandwidth of the near surface interflow and subsurface stormflow was investi... more In a pilot study the bandwidth of the near surface interflow and subsurface stormflow was investigated on a hill slope complex at the military training centre Lizum/Walchen (approx. 2000m above sea level) in Tyrol. High amounts of precipitation (about 250 mm) were applied within 2 days by use of a transportable spray irrigation installation. During the first day water from a creek was applied to the test site. On the following day the site was sprinkled with a salt tracer for an hour followed by creek water for the rest of the day. To characterise the runoff, different measurements techniques were used in the irrigation field. The subsurface runoff was registered in calibrated tanks. Changes in soil moisture were measured with buried TDR-waveguides - arranged in four profiles from 15 cm to 115 cm soil depth in maximum. In addition three geoelectrical profiles were measured. Two geoelectrical profiles were positioned orthogonal to the slope in the precipitation area, where one was re...
For description of runoff formation in alpine catchments still often simple runoff formulas are u... more For description of runoff formation in alpine catchments still often simple runoff formulas are used on the one hand. On the other hand many precipitation / runoff models for assessment of runoff characteristics in mesoscale and microscale catchments require detailed input data and some are using algorithms which don't describe runoff processes "process-oriented". This especially applies to lumped and to
<p>... more <p>In recent years the topic of flash flooding away from rivers and permanent watercourses has attracted increasing attention from the scientific community, public authorities and affected parts of the general public. Not only urban areas with a high proportion of sealed surfaces, but also rural areas have been adversely affected by pluvial flash floods (PFFs) or surface water floods (SWFs) in the recent past. Empirical evidence suggests that amongst others pre-Alpine areas (e.g. in Austria, Germany, Switzerland, ...) might be especially susceptible to this type of flooding. From a water-management perspective knowledge about potentially endangered areas is important for involved stake-holders as a basis for informed decisions on a variety of topics ranging from protection of existing infrastructure and adaptation of current land use practices to future settlement development. In the light of changing climatic conditions also information on projected future developments is highly desirable. With respect to the latter, an increasing number of datasets from national and pan-European climate-services has become publicly available. Also a growing proportion of two-dimensional hydrodynamic models supports direct rainfall as a boundary condition, thus addressing the special requirements for modeling of PFFs/SWFs.</p><p>We utilize different two-dimensional hydrodynamic models (unstructured-mesh, raster-based) in combination with an event-based hydrological approach to simulate the spatial distribution of surface runoff in response to heavy precipitation events for present conditions and under projected future conditions for small rural areas (< 2km²) in Upper Austria. The general applicability of the used modeling approach is demonstrated. However, also a number of remaining challenges related to the limited quantity and quality of observational data for model calibration and the definition of representative future scenarios is identified and discussed.</p>
Shallow soil erosion processes have been increasing within the last decades in the high montane a... more Shallow soil erosion processes have been increasing within the last decades in the high montane and subalpine altitudinal zone of Western Austria. Explanations for the progression of eroded areas in the 2nd half of the 20th century have been subject of various research projects. The studies result in different possible explanations and process catenae regarding triggering effects, material dislocation processes and a following development of the erosive spots. Diverse results are based on different scales of the studies and the specific disciplinary driven approach of the researchers. In order to better understand the process catenae of the dynamics of shallow soil erosion processes this research project is based on an interdisciplinary, pluri-scale approach applied in different areas of the subalpine zone in Western Austria. The focus of this paper is restricted to one catchment area and highlights the influence of different plant parameters on shallow soil erosion processes. The r...
Floods triggered by rain-on-snow events may be a major concern under future climate conditions. T... more Floods triggered by rain-on-snow events may be a major concern under future climate conditions. This is demonstrated by statistically downscaling the results of different GCM experiments (HadCM3, ECHAM4) to three Alpine catchments in Austria. To study the detailed processes taking place within the snow cover and at the soil surface during rain-on-snow events, a hillslope model has been developed. The model is cal- ibrated and validated using experimental data derived from splinkling experiments at different slopes in the Austrian alps. The results of the experiments and of sensitivity studies carried out with the model show that mainly the conditions of the snow cover and of the snow-covered soil, but also the meteorological conditons have a decisive influence on runoff development during rainfall events.
ABSTRACT Simulating heavy rain events to analyze potential surface runoff and related soil erosio... more ABSTRACT Simulating heavy rain events to analyze potential surface runoff and related soil erosion is a well-established approach in alpine ecology and hydrology. In steep and inaccessible terrain with highly variable relief and vegetation, as occurs in mountainous regions, the rain simulators used to date are often not adapted to the abovementioned characteristics. This study reviews heavy rainfall simulators and presents a consequentially developed rain simulator that covers an area of 10 m2. The results of simulated heavy rainfall events (100 mm h− 1) demonstrated the sprinkling equipment used here to be a useful tool, delivering robust results when studying surface runoff at small scales in a heterogeneous terrain. A comparison to rainfall simulation on a 50 m2 plot revealed no significant differences, which demonstrates the equipment used at the scale of 10 m2 to be above a “minimum area” for rainfall simulation. Finally, the impacts of plot size on runoff behavior are discussed to provide useful information using a rainfall simulator in the field. The presented rainfall simulator turned out to be a valuable tool for obtaining more detailed information on the surface runoff of small patterned landscapes (i.e., in both natural and managed grass and dwarf-shrublands) by delivering results comparable to those of larger-scale rain simulators (covering 50 or 100 m2).
Intensive land use by grazing over centuries led to severe erosion at the steep slopes of the Tan... more Intensive land use by grazing over centuries led to severe erosion at the steep slopes of the Tanaser Berg, in the community of Eyrs (South Tyrol - Italy). At the end of the 1970ies grazing was abandoned in the clearly eroded parts of the catchment above the actual timberline and an intensive program for revegetation of the slopes was started by the Department of Hydraulic Engineering, from the Autonomous Province of Bolzano, and the area covered by greening measures divided form the surrounding pastures by a solid fence. In 1999 partial opening for agricultural use by cattle for short term grazing (14 days a year) was planned in the interest of the land owners. Consequentially impact by cattle on the greened areas and alpine lawns still under long term grazing was investigated by use of a transportable spray irrigation for large plots (50 m² size) supplemented by additional investigations (documentation of soil physical properties, characterization of vegetation, changes in plant biomass, etc.). Each plot was irrigated twice: One time before opening the fenced site for short time grazing by cattle again at the End of June and the beginning of July 1999 and a second time five years later, after restart of short time grazing at the beginning of August 2004. In total seven plots were irrigated. 5 plots within the revegetated area, four of them greened, the fifth a carex sempervirens stand, formerly not eroded. 2 of the greened plots were fenced and kept free from grazing over the next five years. In addition 2 carex sempervirens stands with calluna outside which had been grazed at leat for several decades, one of them partially eroded, were investigated as reference plots. The four revegetated plots did not show significant changes in surface runoff development. High content of skeleton (stones and blocs) reduced runoff and erosion potential. In addition high slope-inclination made these plots unloved by cattle. On the contrary the natural carex sempervirens-plot within the revegetated area and permanently grazed calluna heath with carex semperviren outside of the revegetated area, more rich in fine soil, showed a significant increase of surface runoff in torrential rain within the five years. Possible causes for the higher runoff coefficients can be seen in • hydrophobic effects of plant cover and upper humic layer due to very dry antecedent soil moisture conditions in 2004 • Seasonal impact - more intensive loss of plant cover and mechanical impact by cattle (compaction, luting of soil crust) in August 2004. Pasturing in the revegetated areas holds the danger that runoff potential of the not greened / natural plots (carex sempervirens stands) will increase considerably and the concentrated runoff out of these parts will endanger stability of the lower located greened areas.
In hydrology a basic task is the estimation of design discharges and runoff changes in ungauge... more In hydrology a basic task is the estimation of design discharges and runoff changes in ungauged catchments. However, traditional empirical rules of thumb as well as regionalization of measured discharges are subject to uncertainty. It seems that precipitation-runoff modelling is the only comprehensible way to predict discharge alterations due to changes in ungauged basins, even though the results are perhaps not less uncertain. In order to minimize this uncertainty we supplemented a methodology for discharge estimation in ungauged basins by introducing runoff coefficients derived from field assessment, an adapted precipitation-runoff model (ZEMOKOST) and routines for a plausibility check. Subsequently ten gauged Austrian catchments were used as hypothetical ungauged catchments for application and verification of this method. Except for special questions in karst- and glacier-hydrology the procedure showed satisfying results. In addition, the approach has been tested in catchments that have been intensively impacted by human use in the last decades; in this regard variations in discharge and future runoff characteristics have been analyzed.
Floods triggered by rain-on-snow events may be a major concern under future climate conditions. T... more Floods triggered by rain-on-snow events may be a major concern under future climate conditions. This is demonstrated by statistically downscaling the results of different GCM experiments (HadCM3, ECHAM4) to three Alpine catchments in Austria. To study the detailed processes taking place within the snow cover and at the soil surface during rain-on-snow events, a hillslope model has been developed. The model is cal- ibrated and validated using experimental data derived from splinkling experiments at different slopes in the Austrian alps. The results of the experiments and of sensitivity studies carried out with the model show that mainly the conditions of the snow cover and of the snow-covered soil, but also the meteorological conditons have a decisive influence on runoff development during rainfall events.
For description of runoff formation in alpine catchments still often simple runoff formulas are u... more For description of runoff formation in alpine catchments still often simple runoff formulas are used on the one hand. On the other hand many precipitation / runoff models for assessment of runoff characteristics in mesoscale and microscale catchments require detailed input data and some are using algorithms which don't describe runoff processes "process-oriented". This especially applies to lumped and to some conceptual models. Fully distributed models mostly require enormous effort for determining serious catchment description parameters. As a first step into the direction of a time and cost sparing but still process based assessment of runoff development in alpine torrent catchments a two column-procedure has been developed at the BFW in cooperation with university scientists and in cooperation with the Austrian Avalanche and Torrent Control Service and the Bavarian Environmental Agency: 1) Based on the results of about 700 simulations of torrential rain on various soil vegetation complexes and land-use forms in the Eastern Alps a code of practice for assessment of surface runoff coefficients in torrential rain has been developed. By use of three indicator groups (soil conditions, sort and condition of plant cover, way and intensity of land-use / cultivation) runoff coefficients and surface roughness coefficients can be easily attributed to runoff contributing hydrological vegetation units. The big advantage: Dominant infiltration and runoff controlling processes are integrated in the assessed runoff and surface roughness coefficients. The manual is freely available under: http://bfw.ac.at/rz/bfwcms.web?dok=4342 (in German language). 2) The coefficients derived from field studies and/or GIS analysis form input parameters for the precipitation / runoff model ZEMOKOST (The runtime Method of ZEller MOdified by KOhl and STepanek), an MS-EXCEL based calculation tool which can be used with or without GIS-environment. The approach is permanently improved by addition of new features like a linear reservoir approach, antecedent moisture index and torrent control structures like flood retaining basins. The transformation in a GIS-based time-area-approach for a more efficient consideration of site characteristics is in progress. The presented approach has been tested for several years by the Austrian Avalanche and Torrent Control Service and civil engineers as well. In the meantime it has become one of the most frequently used precipitation / runoff procedures in Austria. The latest proof of its reliability has been the successful recalculation of the influence of forests on the enormous flood in August 2005 in the Paznaun Valley (Tyrol, Western Austria).
The aim of the presented project was the development of an automatically algorithm for the estima... more The aim of the presented project was the development of an automatically algorithm for the estimation of the volumetric soil moisture from parameters routinely measured by the aerogeophysical system of the Geological Survey of Austria. Since the measurements of the volumetric soil moisture using passive L-Band-Radiometers are strongly influenced by the damping effect of vegetation cover and the roughness of the ground surface, the new algorithm should be able to compensate these effects (vegetation height < 4 m). To achieve this, four measured parameters of the airborne system were used: vegetation height, vegetation density index, surface temperature (infrared sensor) and brightness temperature (L-Band-Antenna). The Vegetation height and the vegetation density index are calculated from first and last pulse laser altimeter measurements. In the frame of this project an aerogeophysical survey in Lower Austria was performed two times. Simultaneously to the airborne surveys soil moisture was measured by Time Domain Reflectory (TDR) and ground probes were taken. In the laboratory the gravimetric soil moisture and the grain size distribution of the ground probes was determined. For both survey times the vegetation cover was recorded cadastral and an accurate soil mapping was done. For calculating the soil moisture from the airborne measurements an artificial neural network (ANN) was used. One part of the gravimetric soil moisture results from ground probes were used for training the ANN (supervised learning), the other part was used for testing the trained ANN. Furthermore it was tried to use a vegetation classification parameter as an additional input-parameter. Therefore each ground probe was attributed by a vegetation class index. The results for the volumetric soil moisture showed that this extension of the ANN was not improving the outcome. The results of this study show that 1) the correction of vegetation with this method produces a reliable, fast and exhaustive estimation of the volumetric soil moisture in a regional scale. 2) for the development of the algorithm many ground probes, taken at the same time the aerogeophysical survey is performed, are necessary. 3) the influence of the vegetation cover and roughness is much higher than the influence from other soil parameters (geology, soil type, grain size,…) 4) comparison of measured volumetric soil moisture at different times can give information on the water absorption capacity of the top soil.
Rain simulation experiments utilising a transportable spray irrigation installation for the asses... more Rain simulation experiments utilising a transportable spray irrigation installation for the assessment of runoff behaviour on typical runoff contributing areas in alpine catchments have been carried out at the Department of Natural Hazards of the BFW in Austria and the LfU for more than three decades. These investigations usually have been combined with investigations on site characteristics, e.g. information on vegetation and soil. Data from more than 700 single rain simulation experiments have been stored in a joint database and analysed in detail. The first product emerging from these analyses has been the simple “Code of Practice for assessment of surface runoff coefficients in convective torrential rain (version 1.0)” - presented in 2004. It has evolved into a basic means for the derivation of surface runoff coefficient maps, which are needed to calculate peak runoff and runoff amount in torrent catchment areas in case of extreme precipitation, e.g. the recurrent design event. Within the last eight years target-oriented spray irrigation experiments have been continued and new insights into runoff development have been gained. This information and suggestions from practitioners have been incorporated into this present version of the “code of practice (version 2.0)”. This manual comprises advice for the assessment of surface runoff coefficients and surface roughness as well as a function for the calculation of initial abstraction on runoff contributing areas in alpine catchments. A short list of data on velocities of shallow interflow in Central European geological substrates and pictures illustrating typical field situations bring the manual down to a round figure.
Abstract.The Schesa, a sinister contributory torrent to the Ill river near Bludenz (federal
provi... more Abstract.The Schesa, a sinister contributory torrent to the Ill river near Bludenz (federal province of Vorarlberg) is the largest basin-shaped gully of Middle Europe and endangers the underlying villages by torrential debris flow and gigantic mass movements. The catchment is characterized by a complex geological situation, high annual precipitation and torrential rains from spring to early autumn, which cause enormous amounts of surface runoff. Based on field investigations comprising rain simulation experiments on representative plots, investigations on land-use, vegetation cover, soil physical characteristics, geology, hydrogeology and other features of the catchment area, surface runoff coefficient maps were developed. They formed the basis for assessment of runoff potential for different scenarios in vegetation cover and land-use intensity. Calculation of runoff for the recurrent design event by use of an improved run-time method showed the urgent necessity of runoff reduction measures in large parts of the catchment area above the gully. Based on the modelling results a concept for reduction of both, surface runoff and amount of deep percolating water has been elaborated.
Egu General Assembly Conference Abstracts, May 1, 2010
Runoff behaviour of soil-vegetation-complexes as well as the resulting hazard potential are signi... more Runoff behaviour of soil-vegetation-complexes as well as the resulting hazard potential are significantly dominated by their infiltration characteristics. Thus the relation of surface runoff and infiltration and therewith also the runoff coefficient are in the focus of numerous hydrological soil investigations. For this purpose various field methods have been developed during the last decades, among them especially artificial rainfall simulations proved their value. Investigations done by KAINZ et al. (1992, Z. Pflanzenernähr. Bodenk. 155, 7-11) showed that area specific hydrological conditions can be best represented on irrigation plots lager than 40 m². Due to the high heterogeneity of alpine soils and vegetation the usage of smaller plot sizes leads to problems concerning the representativeness of the selected area, the significance of the results and therewith their extrapolation to bigger areas. Furthermore, the smaller the area the more border effects gain in importance. Investigating runoff behaviour of soil-vegetation-complexes by means of rainfall simulations is very cost-intensive and time-consuming. Additionally their application is strongly limited by water availability, especially in the headwaters of the catchment. For this reason we examine if statistical relationships exist that can characterize the outcomes of double ring infiltrometer measurements - which are comparatively easy to realize - and rainfall simulations, especially how many double ring infiltrometer measurements have to be carried out as well as how they have to be positioned to gain representative results. Within the presented study rainfall simulations at ten locations (hay meadows) in the region Innsbruck Land (Tyrol/ Austria) with an intensity of 100 mm h-1 for a simulation period of one hour and 63 double ring infiltration measurements on the same plots were carried out. Furthermore, soils samples were taken for supplementary soil physical analyses. First results of the comparative studies are presented.
Near surface interflow and deep seated interflow can make significant contributions to catchment ... more Near surface interflow and deep seated interflow can make significant contributions to catchment runoff, especially during continuous rainfall events. However, the knowledge about dominant runoff processes, runoff contributing areas and bandwidths of shallow interflow velocities in alpine catchments during continuous rainfall events is still very fragmented. Therefore the following comprehensive approach has been employed in high-altitude sub-catchments of the Wattental in the heart of Tyrol (Austria), to improve the knowledge of catchment properties: • Rain simulation experiments (heavy rain and continuous rain) have been conducted on slopes representative for wider parts of the catchment (geological substratum, land cover, land use,…). Water infiltration and runoff behavior were documented by TDR soil moisture measurements and data collection of several geoelectrical profiles. • Additional geoelectric-profiles have been performed to characterise the geological/hydro-geological sit...
In a pilot study the bandwidth of the near surface interflow and subsurface stormflow was investi... more In a pilot study the bandwidth of the near surface interflow and subsurface stormflow was investigated on a hill slope complex at the military training centre Lizum/Walchen (approx. 2000m above sea level) in Tyrol. High amounts of precipitation (about 250 mm) were applied within 2 days by use of a transportable spray irrigation installation. During the first day water from a creek was applied to the test site. On the following day the site was sprinkled with a salt tracer for an hour followed by creek water for the rest of the day. To characterise the runoff, different measurements techniques were used in the irrigation field. The subsurface runoff was registered in calibrated tanks. Changes in soil moisture were measured with buried TDR-waveguides - arranged in four profiles from 15 cm to 115 cm soil depth in maximum. In addition three geoelectrical profiles were measured. Two geoelectrical profiles were positioned orthogonal to the slope in the precipitation area, where one was re...
For description of runoff formation in alpine catchments still often simple runoff formulas are u... more For description of runoff formation in alpine catchments still often simple runoff formulas are used on the one hand. On the other hand many precipitation / runoff models for assessment of runoff characteristics in mesoscale and microscale catchments require detailed input data and some are using algorithms which don't describe runoff processes "process-oriented". This especially applies to lumped and to
&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;... more &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;In recent years the topic of flash flooding away from rivers and permanent watercourses has attracted increasing attention from the scientific community, public authorities and affected parts of the general public. Not only urban areas with a high proportion of sealed surfaces, but also rural areas have been adversely affected by pluvial flash floods (PFFs) or surface water floods (SWFs) in the recent past. Empirical evidence suggests that amongst others pre-Alpine areas (e.g. in Austria, Germany, Switzerland, ...) might be especially susceptible to this type of flooding. From a water-management perspective knowledge about potentially endangered areas is important for involved stake-holders as a basis for informed decisions on a variety of topics ranging from protection of existing infrastructure and adaptation of current land use practices to future settlement development. In the light of changing climatic conditions also information on projected future developments is highly desirable. With respect to the latter, an increasing number of datasets from national and pan-European climate-services has become publicly available. Also a growing proportion of two-dimensional hydrodynamic models supports direct rainfall as a boundary condition, thus addressing the special requirements for modeling of PFFs/SWFs.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;We utilize different two-dimensional hydrodynamic models (unstructured-mesh, raster-based) in combination with an event-based hydrological approach to simulate the spatial distribution of surface runoff in response to heavy precipitation events for present conditions and under projected future conditions for small rural areas (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 2km&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#178;) in Upper Austria. The general applicability of the used modeling approach is demonstrated. However, also a number of remaining challenges related to the limited quantity and quality of observational data for model calibration and the definition of representative future scenarios is identified and discussed.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;
Shallow soil erosion processes have been increasing within the last decades in the high montane a... more Shallow soil erosion processes have been increasing within the last decades in the high montane and subalpine altitudinal zone of Western Austria. Explanations for the progression of eroded areas in the 2nd half of the 20th century have been subject of various research projects. The studies result in different possible explanations and process catenae regarding triggering effects, material dislocation processes and a following development of the erosive spots. Diverse results are based on different scales of the studies and the specific disciplinary driven approach of the researchers. In order to better understand the process catenae of the dynamics of shallow soil erosion processes this research project is based on an interdisciplinary, pluri-scale approach applied in different areas of the subalpine zone in Western Austria. The focus of this paper is restricted to one catchment area and highlights the influence of different plant parameters on shallow soil erosion processes. The r...
Floods triggered by rain-on-snow events may be a major concern under future climate conditions. T... more Floods triggered by rain-on-snow events may be a major concern under future climate conditions. This is demonstrated by statistically downscaling the results of different GCM experiments (HadCM3, ECHAM4) to three Alpine catchments in Austria. To study the detailed processes taking place within the snow cover and at the soil surface during rain-on-snow events, a hillslope model has been developed. The model is cal- ibrated and validated using experimental data derived from splinkling experiments at different slopes in the Austrian alps. The results of the experiments and of sensitivity studies carried out with the model show that mainly the conditions of the snow cover and of the snow-covered soil, but also the meteorological conditons have a decisive influence on runoff development during rainfall events.
ABSTRACT Simulating heavy rain events to analyze potential surface runoff and related soil erosio... more ABSTRACT Simulating heavy rain events to analyze potential surface runoff and related soil erosion is a well-established approach in alpine ecology and hydrology. In steep and inaccessible terrain with highly variable relief and vegetation, as occurs in mountainous regions, the rain simulators used to date are often not adapted to the abovementioned characteristics. This study reviews heavy rainfall simulators and presents a consequentially developed rain simulator that covers an area of 10 m2. The results of simulated heavy rainfall events (100 mm h− 1) demonstrated the sprinkling equipment used here to be a useful tool, delivering robust results when studying surface runoff at small scales in a heterogeneous terrain. A comparison to rainfall simulation on a 50 m2 plot revealed no significant differences, which demonstrates the equipment used at the scale of 10 m2 to be above a “minimum area” for rainfall simulation. Finally, the impacts of plot size on runoff behavior are discussed to provide useful information using a rainfall simulator in the field. The presented rainfall simulator turned out to be a valuable tool for obtaining more detailed information on the surface runoff of small patterned landscapes (i.e., in both natural and managed grass and dwarf-shrublands) by delivering results comparable to those of larger-scale rain simulators (covering 50 or 100 m2).
Intensive land use by grazing over centuries led to severe erosion at the steep slopes of the Tan... more Intensive land use by grazing over centuries led to severe erosion at the steep slopes of the Tanaser Berg, in the community of Eyrs (South Tyrol - Italy). At the end of the 1970ies grazing was abandoned in the clearly eroded parts of the catchment above the actual timberline and an intensive program for revegetation of the slopes was started by the Department of Hydraulic Engineering, from the Autonomous Province of Bolzano, and the area covered by greening measures divided form the surrounding pastures by a solid fence. In 1999 partial opening for agricultural use by cattle for short term grazing (14 days a year) was planned in the interest of the land owners. Consequentially impact by cattle on the greened areas and alpine lawns still under long term grazing was investigated by use of a transportable spray irrigation for large plots (50 m² size) supplemented by additional investigations (documentation of soil physical properties, characterization of vegetation, changes in plant biomass, etc.). Each plot was irrigated twice: One time before opening the fenced site for short time grazing by cattle again at the End of June and the beginning of July 1999 and a second time five years later, after restart of short time grazing at the beginning of August 2004. In total seven plots were irrigated. 5 plots within the revegetated area, four of them greened, the fifth a carex sempervirens stand, formerly not eroded. 2 of the greened plots were fenced and kept free from grazing over the next five years. In addition 2 carex sempervirens stands with calluna outside which had been grazed at leat for several decades, one of them partially eroded, were investigated as reference plots. The four revegetated plots did not show significant changes in surface runoff development. High content of skeleton (stones and blocs) reduced runoff and erosion potential. In addition high slope-inclination made these plots unloved by cattle. On the contrary the natural carex sempervirens-plot within the revegetated area and permanently grazed calluna heath with carex semperviren outside of the revegetated area, more rich in fine soil, showed a significant increase of surface runoff in torrential rain within the five years. Possible causes for the higher runoff coefficients can be seen in • hydrophobic effects of plant cover and upper humic layer due to very dry antecedent soil moisture conditions in 2004 • Seasonal impact - more intensive loss of plant cover and mechanical impact by cattle (compaction, luting of soil crust) in August 2004. Pasturing in the revegetated areas holds the danger that runoff potential of the not greened / natural plots (carex sempervirens stands) will increase considerably and the concentrated runoff out of these parts will endanger stability of the lower located greened areas.
In hydrology a basic task is the estimation of design discharges and runoff changes in ungauge... more In hydrology a basic task is the estimation of design discharges and runoff changes in ungauged catchments. However, traditional empirical rules of thumb as well as regionalization of measured discharges are subject to uncertainty. It seems that precipitation-runoff modelling is the only comprehensible way to predict discharge alterations due to changes in ungauged basins, even though the results are perhaps not less uncertain. In order to minimize this uncertainty we supplemented a methodology for discharge estimation in ungauged basins by introducing runoff coefficients derived from field assessment, an adapted precipitation-runoff model (ZEMOKOST) and routines for a plausibility check. Subsequently ten gauged Austrian catchments were used as hypothetical ungauged catchments for application and verification of this method. Except for special questions in karst- and glacier-hydrology the procedure showed satisfying results. In addition, the approach has been tested in catchments that have been intensively impacted by human use in the last decades; in this regard variations in discharge and future runoff characteristics have been analyzed.
Floods triggered by rain-on-snow events may be a major concern under future climate conditions. T... more Floods triggered by rain-on-snow events may be a major concern under future climate conditions. This is demonstrated by statistically downscaling the results of different GCM experiments (HadCM3, ECHAM4) to three Alpine catchments in Austria. To study the detailed processes taking place within the snow cover and at the soil surface during rain-on-snow events, a hillslope model has been developed. The model is cal- ibrated and validated using experimental data derived from splinkling experiments at different slopes in the Austrian alps. The results of the experiments and of sensitivity studies carried out with the model show that mainly the conditions of the snow cover and of the snow-covered soil, but also the meteorological conditons have a decisive influence on runoff development during rainfall events.
For description of runoff formation in alpine catchments still often simple runoff formulas are u... more For description of runoff formation in alpine catchments still often simple runoff formulas are used on the one hand. On the other hand many precipitation / runoff models for assessment of runoff characteristics in mesoscale and microscale catchments require detailed input data and some are using algorithms which don't describe runoff processes "process-oriented". This especially applies to lumped and to some conceptual models. Fully distributed models mostly require enormous effort for determining serious catchment description parameters. As a first step into the direction of a time and cost sparing but still process based assessment of runoff development in alpine torrent catchments a two column-procedure has been developed at the BFW in cooperation with university scientists and in cooperation with the Austrian Avalanche and Torrent Control Service and the Bavarian Environmental Agency: 1) Based on the results of about 700 simulations of torrential rain on various soil vegetation complexes and land-use forms in the Eastern Alps a code of practice for assessment of surface runoff coefficients in torrential rain has been developed. By use of three indicator groups (soil conditions, sort and condition of plant cover, way and intensity of land-use / cultivation) runoff coefficients and surface roughness coefficients can be easily attributed to runoff contributing hydrological vegetation units. The big advantage: Dominant infiltration and runoff controlling processes are integrated in the assessed runoff and surface roughness coefficients. The manual is freely available under: http://bfw.ac.at/rz/bfwcms.web?dok=4342 (in German language). 2) The coefficients derived from field studies and/or GIS analysis form input parameters for the precipitation / runoff model ZEMOKOST (The runtime Method of ZEller MOdified by KOhl and STepanek), an MS-EXCEL based calculation tool which can be used with or without GIS-environment. The approach is permanently improved by addition of new features like a linear reservoir approach, antecedent moisture index and torrent control structures like flood retaining basins. The transformation in a GIS-based time-area-approach for a more efficient consideration of site characteristics is in progress. The presented approach has been tested for several years by the Austrian Avalanche and Torrent Control Service and civil engineers as well. In the meantime it has become one of the most frequently used precipitation / runoff procedures in Austria. The latest proof of its reliability has been the successful recalculation of the influence of forests on the enormous flood in August 2005 in the Paznaun Valley (Tyrol, Western Austria).
The aim of the presented project was the development of an automatically algorithm for the estima... more The aim of the presented project was the development of an automatically algorithm for the estimation of the volumetric soil moisture from parameters routinely measured by the aerogeophysical system of the Geological Survey of Austria. Since the measurements of the volumetric soil moisture using passive L-Band-Radiometers are strongly influenced by the damping effect of vegetation cover and the roughness of the ground surface, the new algorithm should be able to compensate these effects (vegetation height < 4 m). To achieve this, four measured parameters of the airborne system were used: vegetation height, vegetation density index, surface temperature (infrared sensor) and brightness temperature (L-Band-Antenna). The Vegetation height and the vegetation density index are calculated from first and last pulse laser altimeter measurements. In the frame of this project an aerogeophysical survey in Lower Austria was performed two times. Simultaneously to the airborne surveys soil moisture was measured by Time Domain Reflectory (TDR) and ground probes were taken. In the laboratory the gravimetric soil moisture and the grain size distribution of the ground probes was determined. For both survey times the vegetation cover was recorded cadastral and an accurate soil mapping was done. For calculating the soil moisture from the airborne measurements an artificial neural network (ANN) was used. One part of the gravimetric soil moisture results from ground probes were used for training the ANN (supervised learning), the other part was used for testing the trained ANN. Furthermore it was tried to use a vegetation classification parameter as an additional input-parameter. Therefore each ground probe was attributed by a vegetation class index. The results for the volumetric soil moisture showed that this extension of the ANN was not improving the outcome. The results of this study show that 1) the correction of vegetation with this method produces a reliable, fast and exhaustive estimation of the volumetric soil moisture in a regional scale. 2) for the development of the algorithm many ground probes, taken at the same time the aerogeophysical survey is performed, are necessary. 3) the influence of the vegetation cover and roughness is much higher than the influence from other soil parameters (geology, soil type, grain size,…) 4) comparison of measured volumetric soil moisture at different times can give information on the water absorption capacity of the top soil.
Rain simulation experiments utilising a transportable spray irrigation installation for the asses... more Rain simulation experiments utilising a transportable spray irrigation installation for the assessment of runoff behaviour on typical runoff contributing areas in alpine catchments have been carried out at the Department of Natural Hazards of the BFW in Austria and the LfU for more than three decades. These investigations usually have been combined with investigations on site characteristics, e.g. information on vegetation and soil. Data from more than 700 single rain simulation experiments have been stored in a joint database and analysed in detail. The first product emerging from these analyses has been the simple “Code of Practice for assessment of surface runoff coefficients in convective torrential rain (version 1.0)” - presented in 2004. It has evolved into a basic means for the derivation of surface runoff coefficient maps, which are needed to calculate peak runoff and runoff amount in torrent catchment areas in case of extreme precipitation, e.g. the recurrent design event. Within the last eight years target-oriented spray irrigation experiments have been continued and new insights into runoff development have been gained. This information and suggestions from practitioners have been incorporated into this present version of the “code of practice (version 2.0)”. This manual comprises advice for the assessment of surface runoff coefficients and surface roughness as well as a function for the calculation of initial abstraction on runoff contributing areas in alpine catchments. A short list of data on velocities of shallow interflow in Central European geological substrates and pictures illustrating typical field situations bring the manual down to a round figure.
Abstract.The Schesa, a sinister contributory torrent to the Ill river near Bludenz (federal
provi... more Abstract.The Schesa, a sinister contributory torrent to the Ill river near Bludenz (federal province of Vorarlberg) is the largest basin-shaped gully of Middle Europe and endangers the underlying villages by torrential debris flow and gigantic mass movements. The catchment is characterized by a complex geological situation, high annual precipitation and torrential rains from spring to early autumn, which cause enormous amounts of surface runoff. Based on field investigations comprising rain simulation experiments on representative plots, investigations on land-use, vegetation cover, soil physical characteristics, geology, hydrogeology and other features of the catchment area, surface runoff coefficient maps were developed. They formed the basis for assessment of runoff potential for different scenarios in vegetation cover and land-use intensity. Calculation of runoff for the recurrent design event by use of an improved run-time method showed the urgent necessity of runoff reduction measures in large parts of the catchment area above the gully. Based on the modelling results a concept for reduction of both, surface runoff and amount of deep percolating water has been elaborated.
Egu General Assembly Conference Abstracts, May 1, 2010
Runoff behaviour of soil-vegetation-complexes as well as the resulting hazard potential are signi... more Runoff behaviour of soil-vegetation-complexes as well as the resulting hazard potential are significantly dominated by their infiltration characteristics. Thus the relation of surface runoff and infiltration and therewith also the runoff coefficient are in the focus of numerous hydrological soil investigations. For this purpose various field methods have been developed during the last decades, among them especially artificial rainfall simulations proved their value. Investigations done by KAINZ et al. (1992, Z. Pflanzenernähr. Bodenk. 155, 7-11) showed that area specific hydrological conditions can be best represented on irrigation plots lager than 40 m². Due to the high heterogeneity of alpine soils and vegetation the usage of smaller plot sizes leads to problems concerning the representativeness of the selected area, the significance of the results and therewith their extrapolation to bigger areas. Furthermore, the smaller the area the more border effects gain in importance. Investigating runoff behaviour of soil-vegetation-complexes by means of rainfall simulations is very cost-intensive and time-consuming. Additionally their application is strongly limited by water availability, especially in the headwaters of the catchment. For this reason we examine if statistical relationships exist that can characterize the outcomes of double ring infiltrometer measurements - which are comparatively easy to realize - and rainfall simulations, especially how many double ring infiltrometer measurements have to be carried out as well as how they have to be positioned to gain representative results. Within the presented study rainfall simulations at ten locations (hay meadows) in the region Innsbruck Land (Tyrol/ Austria) with an intensity of 100 mm h-1 for a simulation period of one hour and 63 double ring infiltration measurements on the same plots were carried out. Furthermore, soils samples were taken for supplementary soil physical analyses. First results of the comparative studies are presented.
Near surface interflow and deep seated interflow can make significant contributions to catchment ... more Near surface interflow and deep seated interflow can make significant contributions to catchment runoff, especially during continuous rainfall events. However, the knowledge about dominant runoff processes, runoff contributing areas and bandwidths of shallow interflow velocities in alpine catchments during continuous rainfall events is still very fragmented. Therefore the following comprehensive approach has been employed in high-altitude sub-catchments of the Wattental in the heart of Tyrol (Austria), to improve the knowledge of catchment properties: • Rain simulation experiments (heavy rain and continuous rain) have been conducted on slopes representative for wider parts of the catchment (geological substratum, land cover, land use,…). Water infiltration and runoff behavior were documented by TDR soil moisture measurements and data collection of several geoelectrical profiles. • Additional geoelectric-profiles have been performed to characterise the geological/hydro-geological sit...
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Papers by Bernhard Kohl
traditional empirical rules of thumb as well as regionalization of measured discharges are subject to uncertainty. It
seems that precipitation-runoff modelling is the only comprehensible way to predict discharge alterations due to
changes in ungauged basins, even though the results are perhaps not less uncertain. In order to minimize this uncertainty
we supplemented a methodology for discharge estimation in ungauged basins by introducing runoff coefficients derived
from field assessment, an adapted precipitation-runoff model (ZEMOKOST) and routines for a plausibility check.
Subsequently ten gauged Austrian catchments were used as hypothetical ungauged catchments for application and
verification of this method. Except for special questions in karst- and glacier-hydrology the procedure showed
satisfying results. In addition, the approach has been tested in catchments that have been intensively impacted by human
use in the last decades; in this regard variations in discharge and future runoff characteristics have been analyzed.
The first product emerging from these analyses has been the simple “Code of Practice for assessment of surface runoff coefficients in convective torrential rain (version 1.0)” - presented in 2004. It has evolved into a basic means for the derivation of surface runoff coefficient maps, which are needed to calculate peak runoff and runoff amount in torrent catchment areas in case of extreme precipitation, e.g. the recurrent design event.
Within the last eight years target-oriented spray irrigation experiments have been continued and new insights into runoff development have been gained. This information and suggestions from practitioners have been incorporated into this present version of the “code of practice (version 2.0)”.
This manual comprises advice for the assessment of surface runoff coefficients and surface roughness as well as a function for the calculation of initial abstraction on runoff contributing areas in alpine catchments. A short list of data on velocities of shallow interflow in Central European geological substrates and pictures illustrating typical field situations bring the manual down to a round figure.
Key words: Cultivation, runoff coefficient, runoff coefficient map, runoff contributing area, runoff delay, shallow interflow, simulation of torrential rain, surface roughness, surface runoff
province of Vorarlberg) is the largest basin-shaped gully of Middle Europe and endangers the
underlying villages by torrential debris flow and gigantic mass movements. The catchment is
characterized by a complex geological situation, high annual precipitation and torrential rains
from spring to early autumn, which cause enormous amounts of surface runoff. Based on field
investigations comprising rain simulation experiments on representative plots, investigations
on land-use, vegetation cover, soil physical characteristics, geology, hydrogeology and other
features of the catchment area, surface runoff coefficient maps were developed. They formed
the basis for assessment of runoff potential for different scenarios in vegetation cover and
land-use intensity. Calculation of runoff for the recurrent design event by use of an improved
run-time method showed the urgent necessity of runoff reduction measures in large parts of
the catchment area above the gully. Based on the modelling results a concept for reduction of
both, surface runoff and amount of deep percolating water has been elaborated.
traditional empirical rules of thumb as well as regionalization of measured discharges are subject to uncertainty. It
seems that precipitation-runoff modelling is the only comprehensible way to predict discharge alterations due to
changes in ungauged basins, even though the results are perhaps not less uncertain. In order to minimize this uncertainty
we supplemented a methodology for discharge estimation in ungauged basins by introducing runoff coefficients derived
from field assessment, an adapted precipitation-runoff model (ZEMOKOST) and routines for a plausibility check.
Subsequently ten gauged Austrian catchments were used as hypothetical ungauged catchments for application and
verification of this method. Except for special questions in karst- and glacier-hydrology the procedure showed
satisfying results. In addition, the approach has been tested in catchments that have been intensively impacted by human
use in the last decades; in this regard variations in discharge and future runoff characteristics have been analyzed.
The first product emerging from these analyses has been the simple “Code of Practice for assessment of surface runoff coefficients in convective torrential rain (version 1.0)” - presented in 2004. It has evolved into a basic means for the derivation of surface runoff coefficient maps, which are needed to calculate peak runoff and runoff amount in torrent catchment areas in case of extreme precipitation, e.g. the recurrent design event.
Within the last eight years target-oriented spray irrigation experiments have been continued and new insights into runoff development have been gained. This information and suggestions from practitioners have been incorporated into this present version of the “code of practice (version 2.0)”.
This manual comprises advice for the assessment of surface runoff coefficients and surface roughness as well as a function for the calculation of initial abstraction on runoff contributing areas in alpine catchments. A short list of data on velocities of shallow interflow in Central European geological substrates and pictures illustrating typical field situations bring the manual down to a round figure.
Key words: Cultivation, runoff coefficient, runoff coefficient map, runoff contributing area, runoff delay, shallow interflow, simulation of torrential rain, surface roughness, surface runoff
province of Vorarlberg) is the largest basin-shaped gully of Middle Europe and endangers the
underlying villages by torrential debris flow and gigantic mass movements. The catchment is
characterized by a complex geological situation, high annual precipitation and torrential rains
from spring to early autumn, which cause enormous amounts of surface runoff. Based on field
investigations comprising rain simulation experiments on representative plots, investigations
on land-use, vegetation cover, soil physical characteristics, geology, hydrogeology and other
features of the catchment area, surface runoff coefficient maps were developed. They formed
the basis for assessment of runoff potential for different scenarios in vegetation cover and
land-use intensity. Calculation of runoff for the recurrent design event by use of an improved
run-time method showed the urgent necessity of runoff reduction measures in large parts of
the catchment area above the gully. Based on the modelling results a concept for reduction of
both, surface runoff and amount of deep percolating water has been elaborated.