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Activity Name:

N-OF01 Overflow Test (Reference)

Activity Numbre:

63

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

Perform an overflow test on a Dutch levee in (visually) good condition. It is considered as a reference case for the Dutch levee in the Hedwige-Prosperpolder.

Activity Brief descriptor

The N-OF01 Reference overflow test has been executed on the landward side of a Dutch levee in the Hedwige-Prosper Polder. The test section is 2 m wide, sided by wooden boarding, and considered to be in a good condition without any visible anomalies. The vegetation state is considered in a state after normal maintenance, with grass lengths of ca. 20 to 30 cm and subject to normal Dutch maintenance methods. Note that the grass may have suffered from the extended dry period from April to September ’20.

Linked to theme(s):

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

Activity Time

Start Date:

Oct. 24, 2020, 8 a.m.

End Date:

Oct. 28, 2020, 5 p.m.

Active time length:

Days:

5

Hours:

None

Other:

30.5 hours effective overflow time.

Location

Levee stretch:

VI

Coordinates/ Latitude (WGS):

51.34842843

Coordinates/ Longitude (WGS):

4.22904

Coordinates/ Altitude (mTAW):

12.0

Descriptor:

Landward slope of levee.

Other references:

Lambert'72 coordinates: X = 140226.0 m Y = 226526.0 m

Data

Data: 1

Data type: Timeseries
Description: Timeseries of Discharge, Water Height and Current Velocity in different positions on the levee slope.
Date availability: June 15, 2022
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/ErTeMm0VuptOkW5eZeLVcvUBMQ5NzhHuMa8Dxezt9EXETA?e=3bhJsy
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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: June 1, 2022
Find at: https://stowanl-my.sharepoint.com/:f:/g/personal/llhpp_stowa_nl/ErTeMm0VuptOkW5eZeLVcvUBMQ5NzhHuMa8Dxezt9EXETA?e=3bhJsy
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Relationships with other activities

Detaled information about the activity

Pre-conditions

Levee slope in visually good condition.

Activity Descriptor

29 blocks of overflow activity for a duration of 30.5 hours. Nominal discharge of 360 L/s. Measured discharge of 330 L/S.

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 test, it was observed that soil eroded slowly and exposed grass roots, without creation of any significant damage that would lead to imminent failure of the levee slope. Near the levee toe edge, a drainage layer became exposed and some of the gravel that was part of that drainage layer, got washed away.

Post-activity conditions

The levee slope stayed in good condition apart from the slight erosion described during the activity. No critical damage.

Immediate Results

A levee slope in good condition is able to withstand a 165 L/s.m discharge for at least 30 hours.

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