Group 6 at the Pieni-Valkeinen > levelling, volumetric- and V-dam measuring

 

Determining inflow and outflow and levelling by group VI

The course of ENVIRONMENTAL FIELD WORK continued first time outdoors, on 19th of September. Our jolly group was formed by third year students; four from China, Wangqing Chen, Xingue Wang, Wenqi Zhang, Qiuwang Fan, one from Germany,  Julia Schmidt  and I, Jani Paukkonen, a local chap.

Picture 1. Thematic map of Pieni-Valkeinen

Levelling


We started our day  by determining levels of two local lakes, Pieni-Valkeinen and Iso-Valkeinen. The work was carried out by a levelling unit shown in the picture below (picture 2.)

Picture 2. Reading height from measuring pole by the shore.

Our team manage to do levelling task pretty well, considering the fact that all my group members were performing this activity for the first time. Our result for the altitude of the lake Pieni -Valkeinen  was over half a meter lower compared to the altitude given in the map. We also determined the altitude of the lake Iso-Valkeinen and this time the difference was approximately 25 cm, even though we had to take several base measurements. Nevertheless, it was a  good task to perform!! 

Levelling tables

Determining inflow and outflow

Second task for the day was to determine the inflow and the outflow of the lake, Pieni-Valkeinen. Our team used two different methods; volumetric- and V-dam measuring. Both are simple to implement, and needs only a short formula to generate result. In the picture 4. and 5. is shown the setup of V-dam (Thompson weir).

 

 





Levelling tables

 

 

 



The green plastic sheet was rather challenging to set on the stream without letting any water to flow aside or underneath. This is, in fact, one of the the major reasons why our flowrates can not be considered accurate. By V-dam, our result for outflow of the lake Pieni-Valkeinen was 3,8 l/s and by volumetric method, the outflow was 3,4 l/s. Volumetric measuring was implemented at the rainwater drum. The idea behind this was was simply to see how much time does it take to fill the bucket. This was repeated four times to get estimation of the average outflow of the lake, Pieni-Valkeinen. Chart 2.

 

 

(chart2.)

 

For the inflow for the Pieni-Valkeinen our result was 1,0 l/s and this was left the only result for the inflow, because we were not capable to find free fall of stream, high enough to set bucket underneath.

 

There is a remarkable difference between inflow and outflow of the Pieni- Valkeinen. Our team came into the conclusion, that the stream in which our measurement was performed,  is not the only source of water for the Pieni-Valkeinen. Precipitation must flow in a wide range of the catchment area of the Pieni-Valkeinen, and this flow do not always leave a visible trace/stream on the surface.

This was excellent task, because the results raised a new questions and challenged us to study reasons for: "how come outflow can be bigger than inflow"!

One another thing we learned, that these experiments on the field require TIME!