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The Leuven Workshop “Soil Erosion and Hillslope Hydrology with Emphasis on Higher Magnitude Events”
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THE LEUVEN WORKSHOP "SOIL EROSION AND HILLSLOPE HYDROLOGY WITH EMPHASIS ON HIGHER MAGNITUDE EVENTS" 27-30 MARCH 1985
This workshop was organized by the Leuven Laboratory of Experimental Geomorphology (DE PLOEY, POESEN, PAULISSEN, GOVERS) in collaboration with AItNERT (Aachen). Its objective was to assess West European research in hillslope hydrology and erosion by rain, wind and mass wasting, with particular attention given to infrequent catastrophic events. The meaning and the applicability of models were also discussed. Soil conservation and efficient management of land and water use are not only important in the tropics and subtropics. CULLETON (EEC) pointed out that several European regions also face these problems. It became clear from the meeting that information on catastrophic events was limited and often poorly understood. Using examples from the Dutch coastal dune belt and from Luxembourg, JUNGERIUS (Amsterdam) concluded that high-magnitude events in these areas were of minor importance compared to events of lower magnitude but higher frequency. The question of erosion hazards and process rates was approached more theoretically by EPPINK (Wageningen) and RIEZEBOS, ROELS and VAN ASCH (Utrecht). A major effort to develop parametric models for hillslope hydrology was made by ROHDENBURG (Braunschweig). There was a general trend to discuss interrill wash and rill or gully development separately. Considerable progress was shown in the understanding of soil surface sealing (GABRIELS, Ghent), crusting (BOIFHN, Paris) and splash erosion on bare soils (POESEN, Leuven). Research by TORRI (Florence) as well as by GOVERS and DE PLOEY (Leuven) resulted in improved understanding of the hydraulics of rill erosion and colluviation. More attention is also paid to deposition on slope sections and in reservoirs in order to elucidate the chronology and geoecological conditions of erosion in catchments (PAULISSEN, Leuven, MUCHER, Amsterdam, BAZOFFI, Florence and SCHICK, Jerusalem). YAIR (Jerusalem) explained some positive effects of erosion and conuviation in arid areas. More research should clearly be focused on the relationship between structural features and erosional systems. MOEYERSONS (Tervuren) discussed crack systems and gully formation and pioneering investigations have been made into the relations between vegetation growth and canopy cover on the one hand and soil erosion and sediment yield on the other (MORGAN, Silsoe, and THORNES, Bristol). STOCKING (Norwich) dealt with soil loss tolerance and the assessment of erosion-induced loss in the productivity of different soil types. Data presented by RICHTER (Trier) resulted in a discussion of the applicability, in Europe, of the Universal Soil Loss Equation (USLE). The prevalent opinion was that the American erosivity parameters and K nomographs cannot be applied in Europe without extensive modifications because of differing climatic and soil conditions. The need was also stressed for more dynamic models which could predict temporal variations in soil loss, particularly high-magnitude events.
404
New techniques for large-scale mapping of erosion were presented by VAN MOLLE (Brussels). Such techniques will facilitate the preparation of soil conservation strategies that are applicable to European field conditions. In relation to this, details of an EEC cooperative project planned in a pilot area near Cesena (Italy) were presented by BAZOFFI (Horence). Improved measurement and experimental techniques make it possible today to examine complex process interactions on a given field plot. Models exist to predict lhirly accurately the effects of processes such as splash erosion and colluviation from rills, provided there is not too much interference by complex biological or soil-structural factors that are difficult to quantify. This was illustrated by a visit to the Huldenberg experimental field plot, 1 hectare in area, of the Leuven Laboratory. The data obtained there are essentially sitespecific. Workshop participants agreed that it was still difficult to apply knowledge that was gained on one site to another site. Perhaps the situation will improve when more measurements and experiments are conducted in the field with the specific aim of pure process analysis as a basis for theoretical models, or in order to validate experiments made with physical models in the laboratory. It seems, however, that extrapolation into wider regions would even then remain of dubious validity.
JAN DE PLOEY, Leuven FRANK AHNERT, Aachen
THE LEUVEN WORKSHOP "SOIL EROSION AND HILLSLOPE HYDROLOGY WITH EMPHASIS ON HIGHER MAGNITUDE EVENTS" 27-30 MARCH 1985
This workshop was organized by the Leuven Laboratory of Experimental Geomorphology (DE PLOEY, POESEN, PAULISSEN, GOVERS) in collaboration with AItNERT (Aachen). Its objective was to assess West European research in hillslope hydrology and erosion by rain, wind and mass wasting, with particular attention given to infrequent catastrophic events. The meaning and the applicability of models were also discussed. Soil conservation and efficient management of land and water use are not only important in the tropics and subtropics. CULLETON (EEC) pointed out that several European regions also face these problems. It became clear from the meeting that information on catastrophic events was limited and often poorly understood. Using examples from the Dutch coastal dune belt and from Luxembourg, JUNGERIUS (Amsterdam) concluded that high-magnitude events in these areas were of minor importance compared to events of lower magnitude but higher frequency. The question of erosion hazards and process rates was approached more theoretically by EPPINK (Wageningen) and RIEZEBOS, ROELS and VAN ASCH (Utrecht). A major effort to develop parametric models for hillslope hydrology was made by ROHDENBURG (Braunschweig). There was a general trend to discuss interrill wash and rill or gully development separately. Considerable progress was shown in the understanding of soil surface sealing (GABRIELS, Ghent), crusting (BOIFHN, Paris) and splash erosion on bare soils (POESEN, Leuven). Research by TORRI (Florence) as well as by GOVERS and DE PLOEY (Leuven) resulted in improved understanding of the hydraulics of rill erosion and colluviation. More attention is also paid to deposition on slope sections and in reservoirs in order to elucidate the chronology and geoecological conditions of erosion in catchments (PAULISSEN, Leuven, MUCHER, Amsterdam, BAZOFFI, Florence and SCHICK, Jerusalem). YAIR (Jerusalem) explained some positive effects of erosion and conuviation in arid areas. More research should clearly be focused on the relationship between structural features and erosional systems. MOEYERSONS (Tervuren) discussed crack systems and gully formation and pioneering investigations have been made into the relations between vegetation growth and canopy cover on the one hand and soil erosion and sediment yield on the other (MORGAN, Silsoe, and THORNES, Bristol). STOCKING (Norwich) dealt with soil loss tolerance and the assessment of erosion-induced loss in the productivity of different soil types. Data presented by RICHTER (Trier) resulted in a discussion of the applicability, in Europe, of the Universal Soil Loss Equation (USLE). The prevalent opinion was that the American erosivity parameters and K nomographs cannot be applied in Europe without extensive modifications because of differing climatic and soil conditions. The need was also stressed for more dynamic models which could predict temporal variations in soil loss, particularly high-magnitude events.
404
New techniques for large-scale mapping of erosion were presented by VAN MOLLE (Brussels). Such techniques will facilitate the preparation of soil conservation strategies that are applicable to European field conditions. In relation to this, details of an EEC cooperative project planned in a pilot area near Cesena (Italy) were presented by BAZOFFI (Horence). Improved measurement and experimental techniques make it possible today to examine complex process interactions on a given field plot. Models exist to predict lhirly accurately the effects of processes such as splash erosion and colluviation from rills, provided there is not too much interference by complex biological or soil-structural factors that are difficult to quantify. This was illustrated by a visit to the Huldenberg experimental field plot, 1 hectare in area, of the Leuven Laboratory. The data obtained there are essentially sitespecific. Workshop participants agreed that it was still difficult to apply knowledge that was gained on one site to another site. Perhaps the situation will improve when more measurements and experiments are conducted in the field with the specific aim of pure process analysis as a basis for theoretical models, or in order to validate experiments made with physical models in the laboratory. It seems, however, that extrapolation into wider regions would even then remain of dubious validity.
JAN DE PLOEY, Leuven FRANK AHNERT, Aachen