Abstract: A method for measuring the water level of a reservoir, a larger river and an underground water and an apparatus thereof comprises a waveguide tube selected in a predetermined length, on the upper portion of which a sonic pulse generator is mounted, and a plurality of sonic receivers (first, second, third . . . nth), such as a microphone, arranged at an interval l from each another, in which the sonic pulse generator generates sonic impulses in a predetermined period, the receivers receive impulses divided into advancing waves and reflecting waves in turns, these impulses are amplified/wave-shaped to be applied to a microprocessor, and the microprocessor measures the time interval t.sub.1 between the advancing wave and the reflecting wave received by first sonic receiver and the time interval t.sub.n-1 between first sonic receiver and the n-1th sonic receiver located close to the water surface so as to calculate the water level L.

Abstract: For the apparatus and method to measure the water depth and level using a gas bubble type level meter, the measurement pipe for water column pressure is composed of plastic pipes of inside diameter of 2-4 mm; two measurement pipes for water column pressure are bounded that the elevation difference between the ends of two measurement pipes for water column pressure is .DELTA.

Abstract: A measurement method for distances between ultrasonic transducers installed on opposite banks of a river or open water channel is provided. Ultrasonic transducer clusters having two transducers spaced by a known distance are used for multichannel ultrasonic flowrate measurement. The distance between ultrasonic transducers installed in the water on both sides of the river is determined by the measurement of the horizontal average flow velocity directly by ultrasonic waves. A calibration and testing method is provided for the distance between two ultrasonic transducers included in the clustered ultrasonic transducer for the calibration and testing method of the flowrate measurement error for a multichannel ultrasonic flowrate measurement system, and for the clustered ultrasonic transducer apparatus.

Abstract: A first measurement unit for untrasonically measuring a flow velocity, a river depth, and an ultrasonic velocity is mounted on floating members. The floating members are connected with a travelling unit for automatically travelling a propeller flowmeter which is used in advance, to thereby measure vertical average flow velocities and river depths at a plurality of positions while moving along a river width. The floating members are provided with ultrasonic vibrators in the center thereof for measuring a river depth and an ultrasonic velocity as well as with ultrasortie vibrator pairs for measuring flow velocities. A second measurement unit for measuring an ultrasonic pulse propagation time period has a unit for calculating an ultrasonic velocity, a river depth, a partial flow quantity and an entire flow quantity, and a unit for controlling movements of the floating members and a distance between the ultrasonic vibrators.