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Activity Name:

N-OF05 Overflow Test (Burrow)

Activity Numbre:

67

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

Perform an overflow test on a location with a large burrow on the levee slope.

Activity Brief descriptor

Linked to theme(s):

Breaching
Animal- & vegetation-induced anomalies
Erosion processes
Temporary levee repairs
Levee survey & monitoring technique
Prolonged collaboration

Activity Time

Start Date:

Nov. 23, 2020, 8 a.m.

End Date:

Nov. 23, 2020, 5 p.m.

Active time length:

Days:

1

Hours:

None

Other:

Total overflow time: 1 hour 19 minutes.

Location

Levee stretch:

VI

Coordinates/ Latitude (WGS):

51.34847

Coordinates/ Longitude (WGS):

4.22893

Coordinates/ Altitude (mTAW):

12.0

Descriptor:

Landward slope of levee.

Other references:

Lambert '72 coordinates X=140257.8 Y=226535.6

Data

Data: 1

Data type: Timeseries
Description: Timeseries of Discharge, Water Height and Current Velocity in different positions on the levee slope.
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/EqQnUHckbSpPtCc3SXmmjCsBw1cRpUTWIgYD6fKFnCIYyQ?e=HC4crq
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Data: 2

Data type: Photo imagery
Description: 2 portals with in total 4 cameras are used to take surface photographs of the levee slope at different times during and in between overflow activity. The surface images in between overflow blocks show damage and vegetation evolution.
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/EmOSFRrdtphJot0zVUxOJJ8BvU0YCFG0qOtJHDv5Cqsldg?e=Acildh
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Relationships with other activities

Detaled information about the activity

Pre-conditions

Large animal burrow midway of the test section. Otherwise, the levee surface state is

Activity Descriptor

Several short runs have been performed out of caution for fast, serious damage. Due to the presence of wire fence in the soil, indicating a prior burrow repair, the soil was somewhat stabilized, but gave way ultimately after little more than 1 hour with a large damage in consequence.

Equipments

Equipment: 1

Overflow generator.
The setup is described in Vercruysse et al. (2022): "Design and application of an overflow generator." (Ref WL2022R20_047_1)

Monitoring & Sensors

- Overhead cameras (4) - Acoustic water height sensors - Electromagnetic current velocity sensors - Discharge sensor (EM or acoustic)
Description of the hydraulic conditions of the overflow. The setup is described in Vercruysse et al. (2022): "Design and application of an overflow generator." (Ref WL2022R20_047_1)

this activity does not have sensors

Limits

During Activity

During the first block of the experiment, the sand mound around the rabbit burrow was washed away, coloring the overflowing water, muddy brown. During the subsequent blocks, the current started to divert around the burrow (due to topographic differences). The current stayed like this for several minutes, whilst the wire fence was slowly being undercut. Finally, after 1 hour and 13 minutes, the test was ended because the cliff that had developed suddenly destabilized and gave rise to a large slope failure.

Post-activity conditions

During the minutes that followed the end of the experiment, it was observed how the head scarp migrated another 2 meters upwards

Immediate Results

Large burrows pose a threat to the levee stability and integrity during overflow.

Results /Conclusion

Factual data report: https://stowanl-my.sharepoint.com/:w:/g/personal/llhpp_stowa_nl/EX5yYnuJ-EBBjoKAxAwg8LkBef8ra9V_-GHjzbkz0Was8g?e=pyaUSq Annexes: https://stowanl-my.sharepoint.com/:w:/g/personal/llhpp_stowa_nl/EWIzoxIhxopCryc6744YgHYBBWr_0fhoGpJ_1pSy0_tM2w?e=pY8Hc6

Infrastructure Knowledge

An integration report will be added later (February 2023) as knowledge document.
The integration report discusses insights gained from both the steady overflow and wave overtopping tests.
under development

Other key information