On-the-fly measurements of large-drop water level and high flow velocity in the closure gap

Being influenced by the factors of water level difference, tide, shortening closure gap, surrounding terrain and riverbed topography, etc., both the variations of flow velocity and water level in the closure gap are markedly larger than those in the general river. The phenomenon will bring potential safety hazards to the reservoir dam under construction, and thus the measurements of flow velocity and water level in the closure gap become very important in guaranteeing the safety of the reservoir dike project. Because of the safety, the measuring accuracy and the instrument performance, the traditional measuring methods of water level and flow velocity are less than ideal. In order to solve the problem, a buoy-based synthetic measuring system, which includes buoy body, balance weight, GPS (Global Positioning System), MRU (Motion Reference Unit), compass and computer, is developed. Besides, a complete data processing method, which includes the data synchronism, attitude correction and quality control of the measuring data, the self-adaptive extraction of water level and the calculation of flow velocity, is put forward in this paper. The system and the method were used for the project of Qingcaosha reservoir closure, and achieved the water level with a bias of less than 7 cm and the standard deviation of ±3.7 cm, and the flow velocity with a bias of less than 7 cm/s and the standard deviation of ±3.8 cm/s, satisfied the accuracy requirements of monitoring water level and flow velocity, and solved the measurement problem in the project.