Abstract
To explicate the process and secular variation of the deterioration of wooden check dams in Nagano Prefecture, an additional investigation, using Pilodyn (a wood density tester), was undertaken of wooden check dams that had been constructed five to six years before the investigation. The results of the overall investigation revealed that the relative frequencies of Pilodyn driving depths of wooden check dams, six years after their construction, yielded a logarithmic normal distribution, and the distribution curve of wooden check dams more than four years after their construction inclined in the positive direction. The ratio of the Pilodyn driving depths of 26 mm or deeper to the overall Pilodyn driving depths was denoted as the deterioration ratio. Regarding the secular variation of deterioration, correlations were observed between the average and standard deviation of the Pilodyn driving depths and the number of elapsed years, and between the deterioration ratio and the number of elapsed years. In other words, the measurements of the Pilodyn driving depths increased with the number of elapsed years—the progress of the dam’s deterioration was confirmed. In wooden check dams without water flow, the acceleration of the Pilodyn driving depth was 3.0∼4.9 mm/year in the dam wings, similar to the 3.9∼4.8 mm/year in the dam bodies. In wooden check dams with water flow, the deterioration velocities of the dam wings and dam bodies were reduced. The acceleration of the Pilodyn driving depth in the dam bodies was found to be reduced to about 2.7 mm/year.
