□ Water level control 　 ● Target water levels for Lake Biwa □ Maintenance and Management of Facilities 　 ● Patrols and weeding of lake levees 　 ● Inspection and maintenance of sluice gates,sluiceways and drainage facilities □ Operation of Facilities 　 ● In drought conditions:internal drainage facilities 　 ● In flood conditions:water supply facilities and gates for water level and bypass aqueducts ■ Gathering Environmental Data in the Lake Biwa Basin 　 ● Hydrologic and meteorological data 　 ● Lake Biwa information provided by comprehensive automatic observation stations 　 ● Lake Biwa water environment survey including submerged plant observation ■Gathering Environmental Data in the Lake Biwa Basin Lake Biwa water environment survey including submerged plant observation Submerged plants are essential in ensuring the well-being of Lake Biwa as well as providing habitats for other living creatures. They therefore function as the core of the Lake Biwa shores ecological system. To assess the water level fall impact on living organisms and creatures, basic biological information capable of serving as a reference for Incorporated Administrative Agency Japan Water Agency must be gathered. Thus submerged plants for the whole area of Lake Biwa are thoroughly investigated during the summer once every few years. Survey points and investigation method ● Diver observation along 109 traverse lines in Lake Biwa. ● For survey purposes, an anchored rope is laid on the bed of the lake, extending from the base point provided at the shore to an offshore point demarcated by the lower limit of vegetation for submerged plants. This serves as a traverse line for surveying. ● The traverse line position is determined by measuring latitude and longitude using GPS (Global Positioning System) from the base point at approximately 200 meter intervals. ● Considering an area measuring 10 m along the anchor rope and 2 m wide as a block (20m2), divers continue to observe visually until the lower limit of vegetation for submerged plants can be confirmed. Diver survey procedure Water depth 100% of block area 90% of block area ・ ・ 10% of block area Sparse (1%) None (0%) A ruler or a bathometer is used to measure water depth up to 0.1 meter and the measurements converted into B.S.L. Vegetation coverage ratio Submerged plant projected areas against the block area are categorized in 10% increments and rankings recorded. B.S.L.: Biwako Basic Surface Water Level Top▲   ■Contact us Copyright(c) 2003 Incorporated Administrative Agency Japan Water Agency Lake Biwa Development Integrated Operation & Maintenance Office All Rights Reserved.