EXPIREMENTNO # 2 Determination of velocity & discharge using floatsAPPARATUS:1) Tape Measure2) Stop-Watch (cell phones often have a timer)3) Meterstick TO Measure Depth (Tape Measures are more Difficult to use)4) Buoyant objects such as orange THEORY:If a Flow Meter is not Available or Rough Estimate is enough so we can usethe float to measure the flow. The float can be any light object such as pinecone or an orange or partially filled plastic water bottle.The basic idea is to Measure the time that it takes a floating object totravel a specified distance downstream.
We measure the flow of stream. Flow isimportant because define the shape, size and direction of the stream. Measure the distance up to 50 feet along the bank string the rope at theboth ends.1.
Using the total stream calculate the crosssectional area of the stream at the both end. To find the total stream widthand the average depth. Total Width (feet)* Average depth (feet) = area in feet.2.
Throw The Float From Upstream Direction. Get astop watch to record the time it takes to reach the downstream. If the floatmoves too fast so record the data 75 or 100 instead of 50 feet. Repeat thisprocess two more times for a total of three measurements.3. Now in this step we will calculate the velocity thedistance covered by float divided by the average amount of time it took tocovered the distance.
If the distance is50 feet and the time taken by orange 100 seconds so get the velocity is 0.5feet/sec. 50 feet/100sec=0.5sec.4.
Calculate the mid-depth velocity by multiplyingthe surface velocity by 0.85. 0.
5×0.85=0.43ft/sec. 5. Now calculate the discharge in cubic feet persecond (cfs) & multiplying the Velocity (ft/sec) by the cross-sectionalarea (ft) of the stream. 0.
43ft/secx10.73ft=4.62cfs. USING A STAFF GUAGE A staff guage is a long ruler placed semi-permanently in a stream orlake used to measure the water depth. Stream guage are the most common &useful measure and therefore emphasized here. We can also place the staff guagein a lake to monitor changes in lake water level.