HYDROMETRY

Hydrometry allows knowing the flow and volume data in a timely and truthful manner. Hydrometric information also makes it possible to achieve greater efficiency in the programming, execution and evaluation of water management in an irrigation system.

The use of ordered hydrometric information allows:

• Provide information for water availability forecasts. This information is important for preparing the water balance and planning the distribution of irrigation water.
• Monitor the execution of irrigation water distribution.
• Hydrometric information also makes it possible to determine the efficiency of the irrigation system and support for conflict resolution.

One of the best known practices to determine the speed of water is:

Current meter

The current meter is an instrument widely used to measure the speed of currents in the sea, rivers, streams, ports, physical models in the laboratory, etc... There are some models that also record their direction, depth and inclination with respect to the vertical, seawater temperature, pressure and conductivity. Its registration modality can be registration ballot, magnetic tape or solid state memory.

In this method, the speed of the water is measured by means of a current meter or pinwheel, which consists of a handle with a propeller or cups connected to the end. The propeller rotates freely and the speed of rotation is related to the speed of the water. A mechanical counter registers the number of revolutions of the propeller that is located at the desired depth. The most used current meters are the propeller ones, of which there are various sizes; the larger the flow rate or the higher the speed, the larger the size of the appliance must also be. Each current meter must have a calibration certificate containing the necessary formula to calculate the speed of the water knowing the number of turns or revolutions of the propeller per second. Current meters are supplied with a formula that relates the speed of rotation of the instrument to the speed of the current. Generally, these devices are used to measure speeds from 1.2 to 5m/s with a probable error of 2%. Like other speed meters, the pinwheel must be submerged under water.

There are several types of current meters, the most used being the propeller ones that are of various sizes; the larger the flow rates or the higher the velocities, the larger the size of the current meter should be.

Each current meter must have a calibration certificate containing the formula to calculate the speed; which are calibrated in hydraulic laboratories: whose general formula is as follows

v = an + b

Where:

v = water velocity (m/s)
n = number of turns of the propeller per second.
a = actual pitch of the propeller in meters.
b = friction speed (m/s)
To obtain the average speed of a water course, the speed must be measured at two, three or more points, located at different depths of the channel section.