1. The Primeval Power of Water
Methods of Measuring
the Speed Flow of the River Drava

2. RUNNING WATER

3. STAGNANT WATER

4. About Drava spring – maximum water level zima – minimum water level
running water
725 km (springs in South Tirol) Danube
Varaždin, Legrad, Belišće, Osijek
length: 719 km
the size of the drainage basin: km2
depth: 4-7 m
spring – maximum water level
zima – minimum water level
the bottom substratum either muddy or sandy
the shore – strewn with rocks
a river which is fast and strong

5. The History of Drava as an Important Water Resource
in the 19th century many hydro-regulatory measures have been taken (before that, a lot of surrounding villages nearby Drava were often flodded – Bukevlje, Levača, Repaš…)
water-mills
hydro-electric power plants (Donja Dubrava)

8. The purpose of water-mills
grinding of grains and making flour
sawing of boards
processing of textile
manufacture of cast iron, etc.

9. What can we measure on a river?

10. pH
pH is a measure of the acidity or basicity of an aqueous solution

11. TEMPERATURE
a physical value by which we express the thermal state of something

12. RIVER WIDTH l

13. RIVER DEPTH h

14. CROSS SECTION

15. DETERMINING THE CROSS SECTION OF THE RIVER DRAVA

16. 1ST PROBLEM OF THE COMENIUS TEAM
utenslis: a ferry, 15 m long cord, grapples, 200 m long cord, measuring tape, an iron object
the problem:
1. find an equation with the help of which we can determine the surface of the cross section of the river Drava
2. draw a curve which describes how the depth of the river Drava changes with its width

17. INSTRUCTIONS
Secure the iron object on a 15 m cord. First measure the width of the river: secure the longer cord on the right bank of the river, and transfer onto the left bank. While returning towards the right bank, measure the depth with the shorter cord.

18. FLOW SPEED
the volume of water which passes through the observed point in a certain time interval

19. Ways of Measuring the Flow Speed
Q = V/t (m3/s)

20. Ultrasonic Flow Meter
based on high-frequent sound waves which are generated by introducing a certain alternative voltage onto the piezoelectric crystal

21. Electromagnetic Flow Meter
the fluid itself works as a voltage conductor, and there are two electrodes on the inner walls of the tube (which are isolated from the tube itself)

22. The Bucket Method measure the volume of the bucket
find a location along the stream
that has a waterfall (or using a weir)
with a stopwatch, time how long it takes the waterfall to fill the bucket with water
repeat steps two and three about six or seven times and take the average

23. v = s/t (m/s) THE STREAMING SPEED
the speed by which the fluid passes through the observed cross section
v = s/t (m/s)

24. MEASURING THE STREAMING SPEED OF THE RIVER DRAVA

25. 2ND PROBLEM OF THE COMENIUS TEAM
utensils: a ferry, stopwatch, measuring tape, bits of paper
the problem:
1. determine the streaming speed of the river Drava at Brodić
2. determine the maximum absolute and the maximum relative errors

26. INSTRUCTIONS climb onto the ferry measure the width of the ferry
after the width of the ferry has been measured, throw bits of paper into the water from one end of the ferry
measure the time needed for one bit of paper to get to the other end of the ferry

27. The Primeval and Unpredictable Power of Water  FLOODS
November 2013, Karlovac (Kupa)
February 2014, Sisak surroundings (Sava)

28. We often forget that the circle of water
is the same thing as the circle of life.
Jacques Yves Cousteau

29. The noblest of the elements is water. (Pindar)
Who does not care for the water, does not care for a better tomorrow. (Old Irish saying)
To a good man, one drop of water is the ocean; to an evil man, the ocean is but one drop of water. (Indian saying)

30. The Primeval Power of Water
Methods of Measuring
the Speed Flow of the River Drava