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Activity Name:

N-OF04 Overflow Test (Reference)

Activity Numbre:

66

Activity type

Strength test

Involved Workpackage

Flood defences
Emergency response
Knowledge infrastructure

Objective

Overflow test N-OF04is a reference test, which means that it is executed at a selected location which is void of any anomaly or obstacle. This test was conducted close to overflow sections N-OF10 and N-OF11 to serve as reference for these two tests.

Activity Brief descriptor

Reference test with additional hydraulic measurements.

Linked to theme(s):

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

Activity Time

Start Date:

Dec. 15, 2021, 8 a.m.

End Date:

Dec. 20, 2021, 5 p.m.

Active time length:

Days:

4

Hours:

None

Other:

25 hours of effective overflow.

Location

Levee stretch:

VI

Coordinates/ Latitude (WGS):

51.34655

Coordinates/ Longitude (WGS):

4.23143

Coordinates/ Altitude (mTAW):

12.0

Descriptor:

Landward slope of levee.

Other references:

Lambert'72 coordinates: X = 140431.5 m Y = 226316.4 m

Data

Data: 1

Data type: Timeseries
Description: 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/Ev6vXCwP_DpChQGv6hWGuqwB9hXkZ1WJ1H3P9XFI1Et49g?e=ZAnqIp
Media avaliable:
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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/EqavdwFClVxNt3XLrqpKXdcBdORLxrrSRV6Cr9PE41x8uA?e=KsLEjU
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Relationships with other activities

  • Activities that are linked to 66/ N-OF04 Overflow Test (Reference) :

    No activities

  • DB_id: 66/ N-OF04 Overflow Test (Reference)

  • DB_id: 66/ N-OF04 Overflow Test (Reference) linked to the following activities:

    DB_id: 88/ P2C Overflow tests

Detaled information about the activity

Pre-conditions

Prior to the test, the section did not appear to have any noticeable discontinuities, such as damage by machinery, irregular vegetation patterns or large animal burrows. Through a thorough visual inspection before commencement of the test a number of smallburrows were detected within and adjacent to the test section. Their depths were in the range of 8-12 cm and their diameters in the range of 3-5 cm, while none of them seemed to have penetrated beyond the clay layer. Their geometry and spatial distribution resembled mice burrows.

Activity Descriptor

18 blocks of overflow for a total of 25 hours of discharge at 330 l/(s.m).. PTV and Lidar measurements on 16/11/2021.

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, surface erosion and burrows were monitored every 2 test blocks of flow. Surface erosion started with the uprooting of grass and exposure of small patches of clay with diameters in the order of 2-3 cm, which gradually expanded and connected with adjacent patches of clay. This is a common pattern that has been observed in all overflow tests. Most of the mice burrows in the test section were within the first patches that formed, which shows that the burrows may have played a role in the early formation of surface erosion. Similar observations in other overflow tests are needed to validate this finding.

Post-activity conditions

Thesefindings are also further discussed in the report concerning burrows in levees (Tsimopoulou & Koelewijn, 2022).

Immediate Results

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

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