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Activity Name:

B-OF02 Overflow Test (Short Grass)

Activity Numbre:

77

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

Perform an overflow test on a stretch with short (mowed) vegetation.

Activity Brief descriptor

The grass cover of the levee has been mowed to a shorter length than standard to evaluate the impact of such shorter grass / vegetation on the resistance against erosion during overflow.

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. 5, 2020, midnight

End Date:

Nov. 7, 2020, 11:59 p.m.

Active time length:

Days:

None

Hours:

21.0

Other:

Location

Levee stretch:

IV

Coordinates/ Latitude (WGS):

51.34134

Coordinates/ Longitude (WGS):

4.23869

Coordinates/ Altitude (mTAW):

11.2

Descriptor:

Lambert'72 coordinates: X=140935.8m; Y=225735.9m.

Other references:

Data

Data: 1

Data type: Factual data report
Description: Factual data report describing the tests on the Belgian part of the HPP levee.
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:w:/g/personal/llhpp_stowa_nl/EVpQIrpc_n1MhDLPmEL2Qh0BgEH8RdDV7ncL0iksYdxubw?e=fvXzeo
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Data: 2

Data type: Monitoring data
Description: - Hydraulic timeseries - Photographs - ... (variable per test)
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/EodB5tuEthlAgGshm3Z6NiMBhlSe7cuxy4Mbaa3dC2eTCQ?e=1lEtER
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Relationships with other activities

  • Activities that are linked to 77/ B-OF02 Overflow Test (Short Grass) :

    No activities

  • DB_id: 77/ B-OF02 Overflow Test (Short Grass)

  • DB_id: 77/ B-OF02 Overflow Test (Short Grass) linked to the following activities:

    DB_id: 88/ P2C Overflow tests

Detaled information about the activity

Pre-conditions

Levee slope in visually good conditions with vegetation cut to +/- 10 cm length.

Activity Descriptor

Overflow during 21:00 hours with a typical discharge of 180 L/s.m over a width of 2 m.

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

An artificial step was dug in the lower part of the levee slope during the last day of testing.

Post-activity conditions

Slope surface shows signs of erosion and barren patches where vegetation is removed, but the clay cover layer is intact. No failure has occurred.

Immediate Results

The overflow during 21 hours leads to some soil erosion and vegetation root exposure, but it does not lead to critical damage or failure. The shorter vegetation does not appear to more or faster erosion than in the reference case B-OF01.

Results /Conclusion

Factual data report + Annexes: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/EvdAZOO-zylAqEWS8-SEiC4BQ5xCAuFXklsysJXnkcVYaQ?e=XDeXq8

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