Qliner deployment in a wild river
May 2004
Introduction
The Eisbach in Munich, Germany, is a quite rough river. The river is a side channel of the river Isar and flows through the scenic English Gardens. The river is just 11 m wide and 1.2 m deep but still the discharge is 25 m3/s. Surface velocities are in the range of 2.5 to 3 m/s. Due to an obstruction below the bridge (right) surface waves are induced.
The goal of these measurements was to see whether the Qliner was able to measure under the difficult circumstances of the Eisbach. Discharge measurements with a current meter can be made from the bridge but require quite some preparation due to the high flow velocities. Other measurements with an Acoustic Doppler Current Profiler mounted on a trimaran type of boat were not successful in the past.
Deploying the Qliner
The measurements were carried out by just two people. One of which was a student who had never seen the Qliner before. The boat was positioned in the river with a rope. The rope was a sort of cableway which makes positioning the boat easy.
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| Fig. 1: Looking downstream from the bridge through the park. |
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| Fig. 2: Side view of the Qliner in the stream. The rope of our small cableway is just visible on the right. |
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| Fig 3: Front view of the Qliner with the wake of the boat clearly visible |
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| Fig 4: A student assisted in the measurement. The measurement was made downstream of the bridge. At the bed below the bridge an artificial obstruction induces waves in the river. |
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A video is available on our website which shows the behavior of the boat during deployment.
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Results:
Fig 5: Results of one of the measurement in an older version of the post-processing software.
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The graphs show the average velocities, the discharge and the segments. The lower right hand side show details such as:
- Measurement time
- Total discharge
- River width
- Mean depth
- Mean velocity
- Expected uncertainty
Three measurements were made on the same position. The table shows the time of the measurements and the results of discharge Q, cross sectional area A and average water depth H. |
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Time
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14:07 – 14:19
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14:27 – 14:41
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15:12 – 15:28
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Q [m3/s]
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25.23
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25.15
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25.89
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Average H [m]
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1.251
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1.244
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1.271
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Measurement accuracy is 1.7 % (standard deviation), fig 5 lower right corner. The standard deviation is for a large extend created by the turbulence in the flow.
Conclusions
We conclude that the deployment was successful. Handling the Qliner was easy and the stability of the boat surprisingly good. Results are accurate |
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