Large floods and climatic change during the Holocene on the Ara River, Central Japan

A reconstruction of part of the Holocene large flood record for the Ara Riv er in central Japan is presented. Maximum intermediate gravel-size dimensio ns of terrace and modem floodplain gravels were measured along an 18-km rea ch of the river and were used in tractive force equations to estimate minim um competent flood depths. Results suggest that the magnitudes of large flo ods on the Ara River have varied in a non-random fashion since the end of t he last glacial period. Large floods with greater magnitudes occurred durin g the warming period of the post-glacial and the warmer early to middle Hol ocene (to similar to 5500 years BP). A shift in the magnitudes of large flo ods occurred similar to 5500-5000 years BP. From this time, during the cool er middle to late Holocene, large floods generally had lower magnitudes. In the modem period, large flood magnitudes are the largest in the data set. As typhoons are the main cause of large floods on the Ara River in the mode rn record, the variation in large flood magnitudes suggests that the incide nce of typhoon visits to the central Japan changed as the climate changed d uring the Holocene. Further, significant dates in the large flood record on the Ara River correspond to significant dates in Europe and the USA. (C) 2 001 Elsevier Science B.V. All rights reserved.