Development of ultrasonic streamflow monitoring system using an existing low head broad-crested agricultural small dam

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Courtesy of HydroVision GmbH

In this study, we developed a system of continuous accurate monitoring of streamflow, which is composed of a pair of ultrasonic Doppler velocity sensors installed on an existing low head broad-crested agricultural small dam. In case of using this dam, errors in computing area are minimized due to stability of it, so that discharge can be accurately measured. In addition, by direct measurement of velocity over dam crest, this system can measure discharge not only for modular flow in which free fall occurs, but also for submerged flow affected by downstream as far as depth and velocity are measured. Preliminary results for 15 dam release events display that discharge obtained by this system is in quite good agreement with dam release and with H-Q relationship. Comparison of volumetric discharge is also made and relative difference with dam discharge is 2.7%.

Keywords: Agricultural small dam, ultrasonic, discharge measurement

Introduction
In this study, we developed a system of continuous accurate monitoring of streamflow. This system is composed of stable cross-section provided by small dam and direct measurement of water velocity passing the crest of the dam. Discharge measurement in the natural river section is affected by instability or fluctuation of bed. On the contrary, this system uses pre-existing or newly made concrete finished small dams which give much more accurate cross-section area than normal riverbed. Since up-looking ultrasonic sensors installed upon the crest of the dam provide accurate vertical velocity profile, mean velocity can be computed. Real-time monitoring of discharge is possible by this system [1],

Outline Of The System
Composition of the system
The concept of the system is shown in Fig. 1. In the system, ultrasonic sensors installed upon the dam crest measure both water velocity and depth. With use of separate pressure level sensors, flood flows of depth up to 10 m may be measured. Fig. 2 shows an ultrasonic velocity sensor and a data logger (model Q-Eye PSC made by German company Hydrovision) used in this study. General specification of the system is given in Tab. 1.

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