Stream flow records obtained at gaging stations serve as a base for the construction of various structures like dams, bridges, culverts, barrages, spillways, etc.
Termanologies in Gaging
“A stream can be defined as a flow channel into which the runoff from a specified catchment or basin drains”
“It is the water surface elevation above an arbitrary datum at a point along a stream”
“It is an instrument used for the purpose of determining stage at the gaging station”
“This is the reach of a channel or a channel section where we can have a unique relationship between stage and discharge”
Stream Flow Unit
Rate of Runoff
“Measured in cubic meter per second or cubic feet per second (cumecs or cusecs)”
Volume of Runoff
“Measured in cubic meters, cubic feet, acre foot, hectare meter etc”
Second foot day
“It is the volume of water collected in one day at a rate of one cubic foot per second”
Selection of Gaging Site
There are the following precautions that should be adopted while selecting the site for gaging in stream.
- Permanence of control
- Opportunityto install an artificial control
- The site should be readily accessible through tout the year.
- The site should satisfy the requirements of depth and velocity measurement in terms of hydraulic characteristics of stream i.e there is no possibility of flow bypassing the site in groundwater or in flood channels.
- The site should be stable and fairly straight and uniform both u[stream and downstream of the site at least four times the normal width of the stream during floods or 0.8 Km whichever is greater.
- Possibility of no back water effect from downstream tributaries or other sources.
- Availability of good metering station where good discharge measurement can be made.
- Availability of site for proper placement of stage gage to record all fluctuations of water level
- Site should be free from debris and other floating matter with respect to control and metering section.
- Availability of power line or telephone line, where needed for special instrumentation.
Measurment of Stage in Gaging
Non Recording Stream Gages
- Staff Type Gage
- Wire Gage
Recording Stream Gages
- Float Type
- Bubble Gage