Page - 332 - in Book of Full Papers - Symposium Hydro Engineering

sounder shall be used for the data collection where GPS signal is unavailable; For topographic survey on the shore, GPS-RTK shall be the main collecting mode while using the total station as assistance. Within 2km of the section in front of dam, the survey shall be carried out as per the scale of 1:200 and the reservoir area as per 1:2000. 2.2. CROSS SECTION SURVEY OF RIVERS IN THE RESERVOIR AREA The latest survey in 2014 covered 72 cross sections of main stream (Fig.1), which were numbered LM09 - LM73, and 8 tributary stream sections of the Gonglang River, numbered LMG01 - LMG04, so the total number were 80 (of which, the A water gauge, B water gauge, lower water gauge and LM73-1 - LM76 for a total of 7 sections were within the warning line of the Xiaowan HPP and were not included in the survey). GPS-RTK real-time dynamic positioning technology shall be used for the layout detection of each end point of the cross section. If the horizontal positioning accuracy is within 3cm and the elevation accuracy is within 3cm, it can be concluded that the end points of the cross section are relatively steady. (1) Two underwater survey plans shall be prepared for cross section survey: First, use the GPS RTK real-time dynamic positioning technology assisted by the multi-beam sounding system for automatic survey, where the point cloud data of the underwater area scanned by the multi-beam sounding system shall be outputted and the underwater topographic points of the cross section line shall be worked out; Second, use the GPS RTK real-time dynamic positioning technology assisted by the HD27 single beam echo sounder for automatic survey and data collection in addition to collecting plane and 3D data of the measuring points. A total station or GPS RTK shall be used to record the plane and elevation data of measuring points for the on-shore part of the cross sections. (2) Before the survey, GPS RTK shall be checked with two or more known points which shall not be put into use before qualification. The measured values are all fixed solutions and information from more than 5 satellites shall be received. (3) The data collection of measurement points by GPS RTK with the assistant HD27 shall be carried out at the space of 3m. The water depth shall also be collected simultaneously and the navigation procedure shall be activated to follow the cross section reference line. (4) The allowable control accuracy of the horizontal measuring points shall not be greater than 0.5m away from the cross section lines. (5) The elevations of the two reference points via the cross section regulation are the same and the calculated distance of the two end points is equal to the accumulated distance of the cross section. (6) The remark column of the survey results of the cross sections shall indicate the properties of each measuring point (e.g. paddy field, dry land, land type, steep canker, cliff, highway, village, water edge, underwater). 332