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  2. Activity : B-OF05 Overflow Test (Large cliff at toe)
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Activity Name:

B-OF05 Overflow Test (Large cliff at toe)

Activity Numbre:

80

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

A large erosion cliff at the toe of the levee is present. This is caused by animals grazing on the levee.

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. 13, 2020, 8 a.m.

End Date:

Nov. 14, 2020, 5 p.m.

Active time length:

Days:

None

Hours:

17.0

Other:

Location

Levee stretch:

IV

Coordinates/ Latitude (WGS):

51.34202

Coordinates/ Longitude (WGS):

4.23764

Coordinates/ Altitude (mTAW):

11.2

Descriptor:

Landward side of levee.

Other references:

Lambert'72 coordiantes: X=140862.90 m; Y=225811.90 m;

Data

Data: 1

Data type: Monitoring timeseries
Description:
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/Ej16vHLzGndMql1HLAjp714BpHrFVvot4KZEbjbjaTn38Q?e=6TDpPX
Media avaliable:
Find media:

Data: 2

Data type: Surface state pictures
Description:
Date availability: None
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/Epi-EudlZXVBmigZf1t7ehIBwxorA34QomkMgzWoHZttVA?e=ZkSb9O
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Relationships with other activities

  • Activities that are linked to 80/ B-OF05 Overflow Test (Large cliff at toe) :

    DB_id: 171/ N-OT03 Overtopping Test (Animal burrow)

  • DB_id: 80/ B-OF05 Overflow Test (Large cliff at toe)

  • DB_id: 80/ B-OF05 Overflow Test (Large cliff at toe) linked to the following activities:

    No activities

Detaled information about the activity

Pre-conditions

The levee slope is characterized by a local, steep cliff of more than 1 meter high near the levee toe.

Activity Descriptor

17 blocks of overflow activity were held, for a total of 17 hours and 4 minutes. The discharge that was close to 320 l/s corresponding to a specific discharge of 160 l/(s.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

During the entire test, no significant damage, other then the normal evolution was observed, until a sudden, massive failure occurred.

Post-activity conditions

The section B-OF05 has developed into a slope instability after 17.1 hours of overflow. The process responsible for this is, however, not exactly known. It is assumed that gradually surface erosion of the cliff area, resulting in steepening of the slope and a cover layer getting thinner, suddenly gave rise to a connection with the sandy core, giving rise to an abrupt failure.

Immediate Results

The presence of animals and vegetation in the area may have promoted the presence of other animals (e.g. mole, rabbit, mice) that created small burrows in the area. Other experiments in Polder2C’s learned that burrows may be a critical feature in levee cover safety. A levee slope may appear stable and in a good shape for an extended period of time. However, during in an overflow event, the evolution from minor to major (decametric) damage may develop within minutes. Saturation of the levee cover sands, which is thought to take several hours to accomplish, may play a role in this fast evolution

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