Name：Tomoki Murakawa

title：Topographical Characteristics of Lake Biwa and Incidents of Water Accidents with a Focus on Water Accidents

academic advisor：Naoyuki Inukai

Recently, many water accidents have occurred in Lake Biwa. In August 2023, 4 water accidents occurred in the west side of Lake Biwa. Then, this paper grasps the topographical features of Lake Biwa, and examines the causes of water accidents which frequently occur in the west side. As a technique, the past accident information and characteristics are grasped from the investigation data, and the features of the accident frequent place are grasped by carrying out the field investigation.
During the 8 years from 2016 to 2023, 22 water accidents occurred, and 16 occurred around Omi-Maiko. From the bathymetry, there is a dense isobath around Omi-Maiko, and there is a sudden increase in bathymetry. About 10 cm/s of reflux occurred in the south direction near Maiko, Omi in summer.
On the accident which occurred on August 18, 2023, the field investigation was carried out in Omi-Maiko Nakahama swimming field. The water depth change in the offshore direction was grasped from the bathymetry. The water depth change from the shoreline to about ten meters was gradual, but increased rapidly around 20 m. At 18 m from the shoreline, a water bottom slope of 28 ° was recorded, and the slope was steep. Bottom sand was collected at the same site. It can be estimated that the median particle size is 1.5 mm and the angle of repose is about 28 ~ 35.2 °.
As the reason why people gather in Omi-Maiko Swimming Area, it is considered that transportation is convenient by JR, and the water quality is good even in Lake Biwa.
Therefore, a safe place for water play in Lake Biwa was selected. As the result, it was considered that Niinohama swimming area and Miyagahama swimming area were comparatively safe.
Even in shallow water, they cannot reach their feet at once and drown. Once it sinks due to the depth of water, discovery and rescue are delayed and cannot be saved. Action is necessary to prevent accidents.