This page is an automatic translation to Croatian of How to measure stream flow rate.This translation is distributed in the hope that it will be useful, but without any guarantee of accuracy.Read more...

Slika 1. Planinski potok koji teče.

Protok je ukupni volumen tekućine koja teče pored fiksne točke u rijeci ili potoku tijekom vremena. Usporediva je s brzinom kojom volumen tekućine putuje kao što se vidi na slici 1. Volumetrijske brzine protoka mogu se mjeriti u različitim jedinicama volumena/vremena kao što su:

• Litre u sekundi (L/s)
• Kubične stope u sekundi (ft³/s)
• Galona u minuti (gal/min)
• Kubični metri u sekundi (m³/s)

Alati za kućanstvo ili specijalizirani mjerači mogu se koristiti za određivanje protoka za cijevi, kanalizacijske sustave i kućanske uređaje. Ljudi koriste podatke o protoku za mikrohidrosustave , sustave otpadnih voda , prikupljanje kišnice , reviziju vode , stope taloženja, statistiku podzemne vode i druge informacije vezane uz vodu . Za pronalaženje protoka većih vodnih tijela kao što su velike rijeke ili iza brana, koriste se mjerači. ^[1]

Ova stranica opisuje niskotehnološke metode za određivanje protoka malih potoka i rijeka, kao i druge alate koji se mogu koristiti u tu svrhu.

Metoda 1: Metoda

Slika 2. Određivanje brzine protoka pomoću kante.

Bucket metoda je jednostavan način mjerenja protoka pomoću kućanskih predmeta. Potrebna je štoperica, velika kanta, a po mogućnosti dvije do tri osobe. Za mjerenje protoka metodom kante:

1. Izmjerite volumen kante ili posude. Imajte na umu da je tipična kanta od 5 galona često zapravo manja od 5 galona.
2. Pronađite mjesto uz potok na kojem se nalazi vodopad. Ako se nijedan ne može pronaći, vodopad se može izgraditi pomoću brane (vidi sliku 4).
3. Štopericom izmjerite koliko je vremena potrebno vodopadu da napuni kantu vodom. Pokrenite štopericu istovremeno s početkom punjenja kante i zaustavite štopericu kada se kanta napuni. Kantu ne treba puniti držeći je ispod površine potoka jer to nije pravi protok.
4. Zabilježite vrijeme potrebno za punjenje kante.
5. Ponovite korake dva i tri oko šest ili sedam puta i uzmite prosjek. Dobro je napraviti nekoliko probnih pokretanja prije snimanja bilo kakvih podataka kako biste mogli steći osjećaj za potrebno vrijeme i mjerenja.
6. Uklonite podatke samo ako se pojave veći problemi kao što su ostaci iz potoka koji ometaju tok.
7. Brzina protoka je volumen kante podijeljen s prosječnim vremenom koje je bilo potrebno za punjenje kante. ^[2]

Evo primjera uz korištenje podataka pronađenih za brzinu protoka Jolly Giant Creeka na terenu Cal Poly Humboldt : Koristeći ove podatke, volumetrijska brzina protoka (Q) jednaka je volumenu kante (V) podijeljenom s prosječnim vremenom ( t).

Metoda 2: Float metoda

Slika 3. Određivanje brzine protoka pomoću plovka i metarskog štapa.

The float method (also known as the cross-sectional method) is used to measure the flow rate for larger streams and rivers. It is found by multiplying a cross sectional area of the stream by the velocity of the water. To measure the flow rate using the float method:

1. Locate a spot in the stream that will act as the cross section of the stream.
2. Using a meter stick, or some other means of measurement, measure the depth of the stream at equal intervals along the width of the stream (see Figure 3). This method is similar to hand calculating a Riemann sum for the width of the river.
3. Once this data is gathered, multiply each depth by the interval it was taken in and add all the amounts together. This calculation is the area of a cross section of the stream.
4. Decide on a length of the stream, typically longer than the width of the river, to send a floating object down (oranges work great).^[3]
5. Using a stopwatch, measure the time it takes the float to travel down the length of stream from step 4.
6. Repeat step five 5-10 times and determine the average time taken for the float to travel the stream. Throw the float into the water at different distances from the shoreline in order to gain a more accurate average.
7. Divide the stream length found in step 4 by the average time in step 6 to determine the average velocity of the stream.
8. The velocity found in step 7 must be multiplied by a friction correction factor. Since the top of a stream flows faster than the bottom due to friction against the stream bed, the friction correction factor evens out the flow. For rough or rocky bottoms, multiply the velocity by 0.85. For smooth, muddy, sandy, or smooth bedrock conditions, multiply the velocity by a correction factor of 0.9.
9. The corrected velocity multiplied by the cross sectional area yields the flow rate in volume/time. (Be sure to keep consistent units of length/distance when measuring the cross section and the velocity e.g. meters, feet)

Method 3: Weirs

Weirs are small dams that can be used in measuring flow rate for small to medium sized streams (a few meters or wider). They allow overflow of the stream to pour over the top of the weir, creating a waterfall, as seen in Figure 4. Weirs increase the change in elevation making the streamflow more consistent which makes flow rate measurements more precise. However, it is very important that all the water in the stream be directed into the weir for it to accurately represent the stream flow. It is also important to keep sediment from building up behind the weir. Sharp crested weirs work best. There are many different types of weirs which include broad crested weirs, sharp crested weirs, combination weirs, V-notch weirs and minimum energy loss weirs.

Figure 4: An example of a V-notch weir.

Method 4: Meters

Meters are devices that measure the stream flow by directly measuring the current. There are many different types of meters but the most common are the Pygmy meter, the vortex meter, the flow probe, and the current meter, described below:

Further reading

To Catch the Rain is the first book created from this much exclusive Appropedia content on rainwater. Thank you for making it happen! Get it digitally here or as paperback on Amazon.

• Wikipedia:Volumetric flow rate
• Volumetric Flow Rate Measurement

References