On 30.09 at the sunny
morning (ok with a small rain...), wearing appropriate professional rubberboots we
started our field work at Pieni-Valkeinen.
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| Proffesional clothes. |
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| Looking for water |
On this first meeting we started our tasks from exploring the terrain and defining the catchment area of the pond. During the walk around the lake, we could observe uphills and some ellevations, that helped us in drawing the drainage basin. This catchment area mostly is a forest and small part is taken by buildings from the city.
We observed that the water comes to this lake
from one main “river” and second smaller input and then goes from the pond
through only one chanel. Water that comes to the lake comes from surrouding uphills and mainly is the drainage water.
Our second task was to
calculate the flow of the incoming and outcomming water. To make this measurement, we used two
different methods. One- Volumetric and the second one using the Thomson weir.
Volumetric way of
meassurments its taking the water into a bucket and noting time and level of a
sample. To have
better results we repeated this test 5 times and then we counted average flow.
Using our results, we
could calculate that the flow of our input (sample 2) is 0,86 l/s and the output is 1,04 l/s. This way of
meaasurments its not really exact, cause we could make many of human mistakes
(to late turning off the time, or wrongly checked the level of the water)
The second way of
checking the velocity of the flow was to use a Thomson weir. To use this weir,
we had to find a appropriate spot – flat under the weir with a slope at the end
(to have a difference in attitude). We prepared our place using the shovel,
really precisely to avoid water escape. After a while we checked the high of
the water level, that cross Thomson weir.
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| Thomson weir. |
Using the measured
results (depth) we could calculate the flow of the river that comes to a pond
(Flow2) and goes out (Flow 1).
FLOW 1
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FLOW 2
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Thomson
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Volumetric
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Thomson
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Volumetric
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2,25 l/s
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1,04 l/s
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0,73 l/s
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0,86 l/s
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Compering the
results from two methods, we can conclude that probably making the exercise
with the outcomming water we made some mistakes cause difference in result is
really big (almost twice bigger). For
some reason the volymetric test from first location have failed (results are not
serious). Maybe we didn’t count the time really gently or there was a mistake
with a level of a water in a box.
Measurments of incoming water, was more exact, cause
the results are similar. Probably because we already knew how to make it, because
it was second measurmetns and we were more accurate.
To
sum up, that was really nice and effective day and as a group, we cant wait for
the next field exercie :)
Thanks for your report. It is always good to check drainage basins borders by foot. In this way you also find out all the other things, like human activities by the lake, which are not visible in the maps. Based on your walking trip, what is most remarkable source of pollutants in the lake concerning negative environmental impact?
ReplyDeleteThere might be some error in your volumetric measurement concerning output stream. First time is always the first time and I think that you focused more on measurements during second time. However, the "fridge box" was not optimal measuring device for this... Sorry about that, it was my mistake.