Determination the velocity & discharge using floatsAPPARATUS:1) TapeMeasure2) Stop-Watch3) Meter stick TO Measure Depth (Tape Measuresare more Difficult to use)4) Buoyantobjects such as orange THEORY:If a Flow Meter is not Available or RoughEstimate is enough so we can use the float to measure the flow. The float canbe any light object such as pine cone or an orange or partially filled plasticwater bottle.
The basic idea is to Measure the time that ittakes a floating object to travel a specified distance downstream. We measurethe flow of stream. Flow is important because define the shape, size anddirection of the stream. Measure the distance up to 50 feet along thebank string the rope at the both ends.
1. Usingthe total stream calculate the cross sectional area of the stream at the bothend. To find the total stream width and the average depth. Total Width (feet)*Average depth (feet) = area in feet.2. ThrowThe Float From Upstream Direction. Get a stop watch to record the time it takesto reach the downstream. If the float moves too fast so record the data 75 or100 instead of 50 feet.
Repeat this process two more times for a total of threemeasurements.3. Nowin this step we will calculate the velocity the distance covered by floatdivided by the average amount of time it took to covered the distance. If the distance is 50 feet and the time takenby orange 100 seconds so get the velocity is 0.5 feet/sec. 50 feet/100sec=0.
5sec.4. Calculatethe mid-depth velocity by multiplying the surface velocity by 0.85. 0.5×0.85=0.43ft/sec.
5. Now calculate the discharge incubic feet per second (cfs) & multiplying the Velocity (ft/sec) by the cross-sectional area (ft) of the stream. 0.43ft/secx10.73ft=4.62cfs. USING A STAFF GUAGE The staff guage is a long ruler placedsemi-permanently in a stream or lake used to measure the water depth. Stream guageare the most common & useful measure and therefore emphasized here.
We canalso place the staff guage in a lake to monitor changes in lake water level. Ifa staff guage place on non-vertical place so knowing that the staff guagereading is correct or not. WHY USE ASTAFF GUAGEWe can use a staff guage to get the informationin an indirect way to calculate the stream flow. If we place the staff guagenear a section of stream for which you are collecting flow data, you can identifythe relationship between stream depth & stream flow. Once you got thisrelationship so we can calculate flow from the stream depth without having totake a time to make a detailed flow measurement.
A staff guage havingnumerically labeled divided in lines to take the measurement of water &calculate easily the depth & stream flow.