親水活動時の滑り事故防止に向けた付着藻類の滑りやすさの定量的評価

摘要

Waterfront activities in rivers and ponds have increased, and ensuring the safety of facilities is an increasing problem. To prevent slip accidents on the bottom of waterfronts, the coefficient of slip resistance (C.S.R') was evaluated quantitatively. The following conclusions were obtained by investigating the relationships between the amount of attached algae, C.S.R', the growth factor of algae and the use of water-friendly structures to prevent slipping. The first is a negative correlation between the amount of attached algae and the C.S.R' of the water bottom; thus the water bottom becomes slippery with the growth of attached algae. The second is that when the nutrient concentration in water is lower than the half-saturation constant, there is a positive correlation between the flow velocity and the amount of attached algae. In contrast, when the nutrient concentration is higher than the half-saturation constant, there is a positive correlation between the light intensity and the amount of attached algae. Therefore, it is possible to create a nonslip condition on the water bottom by managing the nutrient concentration, light intensity and flow velocity. The third is that the water bottom becomes slippery with the growth of attached algae regardless of the type of material.%近年，親水施設の整備が進められ，その安全性が課題となっている。本研究では親水活動時の滑り事故防止を目指し，河川等における水底の滑りやすさ(滑り抵抗係数)の定量的評価を行った。その結果，以下の知見を得た。1)滑り抵抗係数と付着Chl-a量には負の相関があり，付着藻類が増えると滑りやすくなることが定量的に明らかとなった。2)水中の栄養塩濃度が半飽和定数以下の場合，流速と付着Chl-a量に正の相関がある。栄養塩濃度が半飽和定数よりも高い場合，日積算日射量が多い地点で付着Chl-a量も多い傾向がみられた。よって，栄養塩濃度，流速，日射量を管理することで付着藻類の増殖抑制が可能であると推察される。3)付着基質の種類にかかわらず，付着Chl-a量の増加に伴い滑りやすくなった。また，同じ付着Chl-a量では滑りやすい素材のC·S.R'が低くなった。