Author(s): Kuniyoshi Takeuchi
Keywords: Large dams; Sediment trap; USLE; Soil-Rainfall Index; Snake Curve; GEOSS; PUB
Abstract: The global production of suspended sediments to discharge into the ocean is estimated about 20×10 9 t·y -1, of which over 25% may be trapped by about 45,000 large dams constructed around the world. Both sediment production and reservoir trapping are increasing. Sediment production, transport, deposition and its temporal and spatial balance have a major impact on global landscape and upon water and nutrient circulation. These issues need major attention, but are, unfortunately, not well studied on a global basis. A proper sediment production function is not available. The detail global distribution of dam reservoirs, and therefore sediment trapping, is unknown. The USLE (Universal Soil Loss Equation) formula developed by USDA-ARS (Agricultural Research Service) for sheet and rill erosion is literally universally used around the world, including in mountainous regions where landslides and debris flows are the major sources of sediment production. After reviewing the current sediment production studies and information about the global distribution of large reservoirs, this paper introduces the Japanese land slides and debris flow prediction methods, the Soil-Rainfall Index and the Snake Curve. These methods would provide a new alternative for developing a better sediment production function applicable in orogenically active regions of the world. Due to the importance of sediment production and transport in the global water system science, it is concluded that the current GEOSS (Global Earth Observation System of Systems) and GWSP (Global Water Systems Project) plans should include the proper sediment study component as an observation target. The IAHS (International Association of Hydrological Sciences) PUB (Prediction in Ungaged Basins) initiative supports this target since sediment is one of the most important phenomena of ungaged hydrology.