Determination the velocity & discharge using floats
3) Meter stick TO Measure Depth (Tape Measures
are more Difficult to use)
objects such as orange
If a Flow Meter is not Available or Rough
Estimate is enough so we can use the float to measure the flow. The float can
be any light object such as pine cone or an orange or partially filled plastic
The basic idea is to Measure the time that it
takes a floating object to travel a specified distance downstream. We measure
the flow of stream. Flow is important because define the shape, size and
direction of the stream.
Measure the distance up to 50 feet along the
bank string the rope at the both ends.
the total stream calculate the cross sectional area of the stream at the both
end. To find the total stream width and the average depth.
Total Width (feet)*
Average depth (feet) = area in feet.
The Float From Upstream Direction. Get a stop watch to record the time it takes
to reach the downstream. If the float moves too fast so record the data 75 or
100 instead of 50 feet. Repeat this process two more times for a total of three
in this step we will calculate the velocity the distance covered by float
divided by the average amount of time it took to covered the distance. If the distance is 50 feet and the time taken
by orange 100 seconds so get the velocity is 0.5 feet/sec.
the mid-depth velocity by multiplying the surface velocity by 0.85.
5. Now calculate the discharge in
cubic feet per second (cfs) & multiplying the
Velocity (ft/sec) by the cross-sectional area (ft) of the stream.
USING A STAFF GUAGE
The staff guage is a long ruler placed
semi-permanently in a stream or lake used to measure the water depth. Stream guage
are the most common & useful measure and therefore emphasized here. We can
also place the staff guage in a lake to monitor changes in lake water level. If
a staff guage place on non-vertical place so knowing that the staff guage
reading is correct or not.
WHY USE A
We can use a staff guage to get the information
in an indirect way to calculate the stream flow. If we place the staff guage
near a section of stream for which you are collecting flow data, you can identify
the relationship between stream depth & stream flow. Once you got this
relationship so we can calculate flow from the stream depth without having to
take a time to make a detailed flow measurement. A staff guage having
numerically labeled divided in lines to take the measurement of water &
calculate easily the depth & stream flow.