On 7th of October we
met again next to the Pieni-Valkeinen
lake to solve new tasks. The weather was really nice to work outside- without
rain with a small cold (that made amazing atmosphere around the lake). We started with taking water samples from different
place around the lake. Using the special handle we could take a water sample
from a place that is not really close to us. We took this samples from 3
different spots - incomming water to the Pieni Velkeinen lake, outcomming water
and incoming water to the Iso-Velkainen lake.
 |
| Kasia is taking water sample. |
 |
| Otto and Teemu are collecting water sample. |
 |
| Locations of collecting water samples. |
All of the samples we gonna use in the laboratory to check all of the
water parameters. After collecting the samples – we put all important information
on the bottles, like: time, place, date and then we could continue our fieldwork
with the second task.
The aim of our second exercise was to measure the flow of the incoming and
outcomming water from the Pieni-Valkeinen lake using current meter.
We made this measurement
in two places and we marked the results, to calculate the flow of the water. We
had to calculate the turns of the drill
during a half minute, then using the Cross-section of the stream we could calculate
the flow of the stream
.
Flow velocity (m / s)
were calculated using the formula:
𝑉 = 𝑘 ∙ 𝑛 + 𝐷
V = flow velocity (m/s)
D = cross-section of
the stream (m),
n = number of turns
(once/sec)
D = (0.005)
 |
| example of the measurment device. |
In a table we compiled
our scores and results:
Pieni-Valkeinen
Inflow
|
Pieni-Valkeinen
Outflow
|
|
Current meter
|
6,5 r/30s
|
8,5 r/30s
|
Cross-section of the
stream
|
0,041 m2
|
0,034 m2
|
Velocity
|
0,078 m/s
|
0,061 m/s
|
Discharge
|
3,2 l/s
|
2,1 l/s
|
After calculations, we
knew that the water flow for incomming water is 3.2 l/s and for outcoming 2,1
l/s \. Many factors had influence for this results, like: weather, amount of
leafs in the stream, temperature, amount of the rain. When we compare our
results to the results our friends from previuos week, we know that this week
water flow was smaller then the previously one.
Also on 11th
of October, the representation of our group took part in a installing of
groundwater observation next to the Pieni-Velkeinen lake. Now using this installation instead of
surface water we can make also a ground water analyze! So we cant wait for the next meeting!
Thanks for your report. I think that you have got pretty good water samples. Method presented in fig 1 and fig 2 shows us correct use of "special handle".
ReplyDeleteYou have got different results concerning discharge measurement than other group. They measured that outgoing discharge is bigger than incoming discharge. You had that in opposite way. Your calculations are correct but you have also assumed that velocity of water is same in every point of stream. It is not, there is bigger flow resistance near bottom, surface and sides. If you measure only maximum (using only one point) velocity with current meter, the discharge will be bigger than real situation. It would be wise to split stream into a smaller parts and make several measurements with current meter.
You can find more information about water velocity in open channels from literature. Please, check slide 16 from following lecture notes:
http://www.slideshare.net/RambabuPalaka/open-channel-flow-57084579
It was nice that also your group was present when new groundwater monitoring well installed! It was nice to see professionals in action.