SPECIAL ISSUE DRIP-SCREEN RAINFALL SIMULATORS FOR HYDRO- AND PEDO- GEOMORPHOLOGICAL RESEARCH: THE COVENTRY EXPERIENCE I. D. L. FOSTER 1 , M. A. FULLEN 2 *, R. T. BRANDSMA 2 AND A. S. CHAPMAN 1 1 Centre for Environmental Research and Consultancy, NES (Geography), Coventry University, Priory Street, Coventry, CV1 5FB, UK 2 School of Applied Sciences, The University of Wolverhampton, Wolverhampton, WV1 1SB, UK Received 27 April 1999; Revised 19 January 2000; Accepted 27 January 2000 ABSTRACT Seven case studies are presented, demonstrating the successful use of a laboratory-based drip-screen rainfall simulator at Coventry University to investigate several hydrological, pedological and geomorphological problems. The results of previously unpublished studies are presented in full, while the salient points of published studies are discussed. Synthesis of the experimental results led to the recognition of various philosophical and practical problems associated with the realistic simulation of rain, which need to be addressed in future research. Particular problems are posed by the variety of analytical approaches and simulator designs, as they impede meaningful inter-laboratory comparisons. It is argued that future improvements require optimization, harmonization and standardization of analytical procedures and rainfall simulators. An ideal approach would be the development of a European key laboratory to offer realistic and standardized simulation conditions. Copyright # 2000 John Wiley & Sons, Ltd. KEY WORDS: drip-screen rainfall simulator; infiltration; soil aggregate stability; soil erodibility; soil translocation; urban runoff INTRODUCTION Laboratory-based rainfall simulation studies have been widely used to investigate many hydrological, geomorphological and pedological problems. Many rainfall simulators have been described (e.g. Swanson, 1965; Morin et al., 1967; Bryan, 1969, 1977; Hall, 1970; Selby, 1970; De Ploey et al., 1976; Riezebos and Seyhan, 1977; De Ploey and Gabriels, 1980; Singer et al., 1980; Moeyersons, 1983; Pilgrim and Huff, 1983; Luk et al., 1986; Bowyer-Bower and Burt, 1989; Robinson and Naghizadeh, 1992; Morgan, 1995). Broadly, these fall into three major systems: sprays, rotating sprays and drip-screens. Spray systems often deliver rainfall in pulses to the ground, whilst rotating sprays can deliver rainfall over a relatively large surface area, but rainfall intensity usually decreases with distance from the rotating nozzle. Attempts to reduce this spatial variability frequently rely on multiple rotating nozzles, with the overlap distance between the sprayers being determined by the area over which the simulation is to be performed. Spray systems often achieve rainfall delivery at terminal velocities approaching that of natural rainfall. Drip systems, using hypodermic needles or drop formers, are usually used over relatively small surface areas, but are often considered unsuitable owing to the difficulty in raising the drip-screen to sufficient height to achieve representative terminal velocities (Bubenzer, 1979; Hudson, 1981). Various factors influence the choice of delivery system, including the purpose of the experiment, the drop-size distribution of the simulated rainfall, the raindrop terminal velocities and the small-scale spatial variability in rainfall delivery. Earth Surface Processes and Landforms Earth Surf. Process. Landforms 25, 691±707 (2000) Copyright # 2000 John Wiley & Sons, Ltd. * Correspondence to: M. A. Fullen, School of Applied Sciences, The University of Wolverhampton, Wolverhampton, WV1 1SB, UK. E-mail: M.Fullen@wlv.ac.uk Contract/grant sponsor: MAFF