NO # 2
Determination of velocity & discharge using floats
Stop-Watch (cell phones often have a timer)
stick TO Measure Depth (Tape Measures are more Difficult to use)
Buoyant 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 water bottle.
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
Using 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.
Throw 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 measurements.
Now 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
Calculate 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.
A 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 STAFF GUAGE
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 &