Despite a steep increase in dam removal projects, there are few studies on the biophysical responses to dam removal. In this study, we evaluated the short-term (1.5 years) and long-term (5.5 years) effects of partial check dam removal on fish assemblages and their habitats. First, the habitat preferences of fish were examined at a channel unit scale: pools, rapids, and side channels satisfied the seasonal habitat requirements of the fish assemblages. Partial check dam removal increased the abundance of these habitats and diversified the habitat structures owing to the sediment release from the dam; in contrast, the bedrock distinctly decreased 1.5 years after dam removal. However, 5.5 years after dam removal, the bedrock proportion increased, and the habitat structures were simplified again owing to the re-transportation of sediments. Similar temporal changes were also determined through a reach-scale analysis with a change in the bed materials. Anadromous Oncorhynchus masou began to spawn and recolonize in the upstream section of the dam after the dam removal, causing similar assemblage compositions between the downstream and upstream sections. The abundance of Salvelinus malma and Noemacheilus barbatulus toni in the upstream reaches decreased over time after the dam removal. The temporal changes in the biophysical responses suggest that long-term monitoring is indispensable for the reliable evaluation of dam removal effects.

Abstract"Priority Urban Redevelopment Areas" in Tokyo, Japan, are currently undergoing large-scale urban renewal. However, the heat island phenomenon has become a serious problem in large cities in Japan.We surveyed the temperature and wind conditions in two adjacent areas: a new skyscraper district on the coast (A district) and a typical inland urban district (B district). Our observations indicated local temperature increases and unstable wind with weak velocity in B district.It is possible that differences in the wind environment infl uence the local temperature. We analyzed the relationship between undulations in ground level and the wind environment by wind tunnel experiments. The results confi rmed that there was a weak wind area in B district located behind A district from the direction of the coastline.Our fi ndings indicate that it is important to consider the heat island phenomenon in urban planning in order to make best use of the cooling effect of the breeze from the sea at waterfront areas.Keywords: cooling effect of the sea breeze; heat island phenomenon; urban structure