4. Location of Current-Meter Stations

Whenever possible, current-meter gaging stations should be located in straight, uniform stretches of channel having smooth banks and beds of permanent nature. The station should be located far from flow disturbances caused by turnouts and power stations. These flow disturbances will variably affect the relationship of discharge to gage height. In many channels, these conditions are difficult to find, and unusual care must be taken to obtain a satisfactory location.

The changing nature of some rivers and canals may require frequent current-meter measurements. Sand shifts may occur frequently, often daily, and aquatic weeds may continue to grow and increase in area. To obtain the gage-discharge relationship at stations on such streams, current-meter measurements may be necessary two or three times weekly or perhaps daily if the importance of equitable water distribution justifies such action. A rating section consisting of a short-lined section in a straight stretch of channel will ensure a meter station of unvarying dimensions if the sediment problem is not serious. Such a section in a canal is shown on figure 10-1.

Figure 10-1 -- Current-meter station on a canal, viewed from upstream. Current-meter measurements are taken from the bridge, and the sheltered stilling well houses an automatic water-stage recorder..

A gaging station located upstream from any permanent single control section, such as a drop, will usually have a simple relationship between the gage height and discharge. A gaging station located in a river may have successively changing control points downstream as discharge increases or decreases, resulting in more complicated gage height versus discharge relationships. The last two types are not commonly used in irrigation practice and will not be discussed.