Mìøení prùtoku, Metoda è.1
Malé proudy

Lets assume some more.  Lets say you'regoing to divert about 1/2 of your flow through a pipeline for power needs. If the volume is relatively small, you could use a measured container likea 55 gal drum, a garbage can or what ever.  Just divert the wateras directly (no restrictions) into it and measure how long in seconds ittakes to fill it up to a certain point you've previously marked off. Lets say you gave a 55 gal drum.  It measures 42 in high.  Youcan fill it to overflowing in 126 seconds.  The equation is:

The most reliable method for measuring streamflows above 1 CFS is the Weir.  The weir is usually a temporary structurealthough if you there's no not reason to make it permanent is you wish. As you can see it's basically a dam with a slot of specific with &depth cut into it.  As you can see the 3 edges of the slot are beveledto about 30 degrees.  Oh yea, when you construct it, leaks aint allowed! A stiff board is set up parallel exactly 4 feet up stream from the weir. A second board it that laid between the weir & the first board. Your going to level this second board as precise as you can.  As wateris flowing through the slot in the weir the water

upstream will not be parallel with your "leveled board"  If the Slot were not in the Weir and water just flowed over the top then the surfaceof the water would just about be parallel with the 2nd board.  Howeverwith the slot the surface of the water is shallower at the weir end thanthe board 4 feet up stream.  Now take a ruler and set it on the bottomof the weir cut & them mark the point where it intersects the top ofthe 2nd board.  Move the ruler back now to the 4 foot point. Makesure the mark you just made is aligned then the top od the 2nd board atthe four foot mark.  Now measure up from the bottom of the ruler tothe water level.  If the slot were 6 feet wide and you measured awater depth of 8 inches then the flow through the weir as indicated bythe chart would be 10.8 CFS.
 
 

This is actually pretty simple.  It can also be used any any ofthe above situations when building a weir in not possible or practical. You pick a length of river or stream that you can get to.  Lets saywe have a small river 55 feet wide and a depth going to 6 feet.  Alsoassume we have a straight section we can get to that is 70 feet long. We kind of need to believe that the cross section of the river is symmetricalfor the 70 feet. Being to deep to wade we need a boat!

Stretch a strong rope or cable across the river.  Made sure itstight.  Have the cable marked at even intervals.  Lets say every2 feet.  You'll need at partner to hold on to the cable and hand overhand the boat across the stream.  At every marked interval you, inthe back of the boat, use a measuring stick & record the water depth. What your doing is plotting the contour of the river bottom.

If you don't remember your trigonometry, then get your daughter to calculateout the cross section for you.  Sons aren't to good at this yet, unlesshe's an engineering student in his senior year in college.  Youngerones have to much on their minds. (girls, music, girls, cars, girls) Failingthat, go down to Wal-Mart & by yourself a pack of graph paper &plot you reading out & count the squares.  That's what I'd do. I hate math!

Lets assume you did all that and you came up with a cross section of335  feet. Now get your self a float. A milk jug will do just fine. Now suspend a weight about 3 feet away from the jug.  Keep in mindthat you want the water to carry the weight not the float. Another jug filled with water would be almost a perfect thing to use. Nowrelease your float at the start of the 70 foot run in the middle of theriver and time how long it takes to travel to 70 feet (or what ever didtanceyour using.)

Let's say now that you've done this several times and found the averagetime it takes your float & weight to travel the 70 feet is 112 seconds.Multiply the time in seconds by the cross section in square feet. In the case above it's