Abstract
River environments must be managed appropriately if we are to take a strategic approach to river rehabilitation. For appropriate management we often need to use river environmental information that was collected a long time ago. There is an increasing need for support systems to help us use this information, but most of the acquisition and recording of environmental information still depend on analog data or qualitative information, including photographs, maps, or the memories of elderly long-term inhabitants of the area. Meanwhile, the development of electronic information-gathering techniques has progressed rapidly in recent years. Environmental information is now being acquired digitally - for example, by the use of GPS to take positional information on living organisms or laser profiling to gather terrain information. We used both analog and digital data to establish a connection between environmental conditions - especially hydrological ones - and the presence of the native damselfly Mortonagrion hirosei Asahina and various plants. We found that the bulk of the larvae (57%) were present at points with cumulative inundation times of 1 to 500h, 1% to 9% inundation probabilities, and a Y. P. range of 0.2 to 0.6 m. Our results suggested that the best landform conditions for the exit of many larvae were based on the connectivity of water and soil flow with soil deposits by plants. Interestingly, the optimum ecological performance of the larvae differed from that of the population of the common reed Phragmites australis. In planning to manage river environments, if we can utilize both analog data and digital GIS data appropriately then we will be able to predict adequately the influences on river ecosystems and apply this information to monitoring after river rehabilitation.
