Erosion, Transport and Deposition Processes

The first paper by H.-R. Bork commemorates Heinrich (Heiner) Rohdenburg, who worked until his too far to early death in 1987 as a Professor of physical geography and landscape ecology at the Technical University of Braunschweig, FRG. We owe a major part of our knowledge about the quaternary landscape evolution and recent erosion processes in Central and Southwestern Europe, in the subtropics and tropics to Heiner Rohdenburg. He initiated and coordinated many geomorphological, agro- and geoecological research projects. The exceptional work of Heiner Rohdenburg resulted in the establishment of the course of "Geoecology" and in the foundation of the interdisciplinary Special Collaborative Program 179 "Water and Matter Dynamics in Agro-Ecosystems" at the Technical University of Braunschweig. The main objectives of this longterm program are the analysis, simulation and forecasting of effects which farming and natural properties have on energy and water fluxes, matter dynamics, micro-climate and soil organisms in agro-ecosystems. A general paper by J. De Ploey points out the major contributions of Heiner Rohdenburg to geomorphology and geoecology in analyzing and closing the link between the longterm evolution of landforms in a geological time frame and the present-day erosion, transport, and deposition processes. J. DE PLOEY discusses geomorphological models and the still existing gaps between soil loss modeling based upon experimental plots only and field reality. Studies of the processes of splash erosion, sheet erosion, and gully erosion are the topics of the following five papers. J. Schmidt leads off this group investigating the impact of rainfall on the sediment transport by sheetflow. The response of semi-arid and arid soils to simulated heavy rainfall was studied by H. Lavee, A.C. Imeson, S. Pariente and Y. Benyamini in the Judean Desert. At three locations along an altitudinal transect with a climatological gradient the relations between infiltration, runoff generation, sediment production, and solute release have been analyzed. M. Cervera, N. Clotet, R. Guardia and L. Sole-Sugranes describe the processes of runoff generation and erosion under simulated heavy rainfall in scarcely vegetated and non-vegetated badlands in Northern Spain. The paper of P.D. Jungerius and J.W. van den Brink focusses on the processes which are responsible for the formation of gully walls. Using geomorphological mapping methods and process based terrain classifications the development of a V-shaped gully in Northern Morocco is analyzed in detail. Processes and factors controlling the development and pattern of gullies are examined by D.J. Oostwoud Wijdenes and R.B. Bryan. Active shallow gully networks as well as rapidly developed deep badland gully systems were studied on the Njemps flats in Northern Kenya. As the concluding section there are five papers dealing with the modeling of water fluxes at the soil surface and in the soil, splash erosion and sheet erosion processes. The various approaches for modeling rainfall - runoff relationships of bare soils affected by surface sealing are reviewed by Y. Mualem and S. Assouline. They present and calibrate a soil sealing model which has been developed in cooperation with Heiner Rohdenburg. This model simulates the dynamic changes of the soil hydraulic properties within the zone of the soil seal layer using data of two saturated soils. J. Schmidt offers a mathematical model that simulates rainfall erosion. Disaggregating sediment transport capacity into detachment rate and sediment travel distances M. KIRKBY investigates and estimates travel distances as a significant variable in particulate movement. D. Torri and L. Borselli introduce and discuss physically based equations which describe flow detachment, sediment transport and interactions between flow characteristics (e.g. flow velocity and transport capacity) and sediment load. B. Diekkrüger, R.E. Smith, D. Krug and R. Baumann discuss the applicability and transferability of the process based model OPUS which simulates the water fluxes at the soil surface and in the soil and the erosion processes at slopes with homogeneous soil conditions. Meteorological and soil hydrological data which were measured in a catchment in Northern Germany have been used by the authors to validate OPUS. These data were collected in the framework of the major research program "Water and Matter Dynamics in Agro-Ecosystems" of the Technical University of Braunschweig which was initiated and coordinated, until his early death, by Heiner Rohdenburg. Reflecting the wide range of geomorphological, hydrological, pedological, and geoecological research fields of Heiner Rohdenburg the papers of this CATENA SUPPLEMENT vary from general diagnoses and considerations concerning the evolution of landscapes, process studies in the laboratory and in the field to process-orientated models. Honouring the extraordinary, ecosystem-orientated work of Heiner Rohdenburg, the papers present the state of the art, indicating many directions for future research.