Key Categories of Hydrological Measuring Instruments: From Water Level to Water Quality Monitoring

Hydrological measuring instruments are specialized devices for monitoring and collecting information on hydrological elements. According to different measurement objects, they can be classified into categories such as water level, flow rate, precipitation, water quality, and sediment measuring instruments.

Water Level Monitoring Stations are used to obtain the elevation of the water surface. Common types include float-type water level gauges, pressure-type water level gauges, and ultrasonic water level gauges. Float-type water level gauges use a float that rises and falls with the water level to drive a mechanical structure, converting displacement into electrical signals or mechanical readings. Pressure-type water level gauges utilize the corresponding relationship between underwater pressure and water depth, calculating the water level through a pressure sensor. Ultrasonic water level gauges emit ultrasonic waves and measure the water level height based on the round-trip time of the sound waves, making them suitable for non-contact measurement scenarios.

Flow measuring instruments are used to calculate the volume of water passing through a specific cross-section per unit time. The main types include current meters, ultrasonic flowmeters, and electromagnetic flowmeters. Current meters (such as propeller-type and cup-type) measure the water flow velocity and calculate the flow rate by combining it with the cross-sectional area. Ultrasonic flowmeters calculate the flow velocity using the difference in the propagation speed of sound waves in downstream and upstream directions, without the need to contact the water body. Electromagnetic flowmeters are based on the principle of electromagnetic induction; they obtain the flow velocity by measuring the induced electromotive force in conductive water bodies, and are suitable for measuring water flow in pipelines or channels.

Precipitation measuring instruments are mainly rain gauges, which are divided into tipping-bucket rain gauges, siphon rain gauges, and weighing rain gauges. Tipping-bucket rain gauges accumulate rainwater until the bucket tips over, and the number of tips is recorded to convert into rainfall amount. Siphon rain gauges use the siphon principle: when rainwater accumulates to a certain volume, it is automatically drained, while the precipitation process is recorded. Weighing rain gauges directly measure the accumulated precipitation through a weighing sensor and can adapt to special precipitation forms such as snow and hail.

There are also sediment measuring instruments (such as laser particle size analyzers and isotope sediment meters, used to measure the sediment content and particle size in water) and water quality measuring instruments (such as pH meters and dissolved oxygen meters, used to monitor the chemical indicators of water bodies). The coordinated use of different instruments enables comprehensive monitoring of the hydrological system, providing data support for flood control, water resource management, and water conservancy project construction.