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Dam Breach - Erosion

Dam Breach - Erosion#

Overview

In this tutorial, an erosion dam breach with failure is created. In this instance, the reservoir is filled but the pre-reservoir elevation is known.

Required Data

The required data is in Module 6.

File

Content

*.qgz

QGIS data files

*.gpkg

FLO-2D Geopackage

*.tif

Grid elevation

Step 1: Load the project#

  1. We are finished with the previous project. Save and close it.

  2. Start with the project from Module 6.

  3. If necessary, load it into QGIS. Open QGIS and drag the Erosion Breach Module 6.qgz file into the project.

  4. Save the project.

../_images/Module222.png

  1. Click Yes to load the model.

../_images/Module223.png

Step 2: Initial conditions reservoir#

  1. An initial condition is set to fill the reservoir when FLO-2D PRO.exe initiates the simulation.

  2. Set up this condition in QGIS.

  3. Click the collapse widgets button.

  4. Open the Initial Condition Editor widget.

  5. Click the add reservoir button.

../_images/Module224.png

  1. Place a reservoir node anywhere within the reservoir area and fill the form. Click ok to close the data.

../_images/Module225.png

  1. Click the Save button and the Schematize button on the widget.

  2. This data is saved to the INFLOW.DAT file when the model is exported.

../_images/Module226.png

Step 3: Review dam geometry#

Crest width = 32 ft

Crest length = 7900 ft

Shell slope US and DS = 2

Core slope = 0.5

../_images/Module227.png ../_images/Module228.png

Step 4. Review dam material#

Each variable is discussed in the Data Input Manual BREACH.DAT tab. This data may be available from the original dam construction manual or from periodical safety reports. Check with the dam owner, or dam safety agency for data.

Value

Variable

Description

0.1

d50c

d50 core (mm)

0.35

porc

porosity core

120

uwc

unit weight core (lb/ft3)

0.15

cnc

roughness n core

33

afrc

angle of internal friction core(degrees)

750

cohc

cohesive strength core (lb/ft3)

50

unfcc

sediment gradient ratio

50

d50s

d50 shell (mm)

0.4

pors

porosity shell

100

uws

unit weight shell (lb/ft3)

0.2

cns

roughness n shell

32

afrs

angle of internal friction shell (degrees)

250

cohs

cohesive strength shell (lb/ft3)

10

unfcs

sediment gradient ratio

0

grasslength

grass length downstream face (in)

0

grasscond

grass condition downstream face (0 or 1)

0

grassvmaxp

maximum permissible velocity (fps)

300

d50df

d50 downstream face (mm)

2

unfcdf

sediment gradient downstream face

Step 5. Review general breach parameters#

Each variable is discussed in the Data Input Manual BREACH.DAT tab.

Value

Variable

Description

2500

brbotwidmax

Maximum width to constrict the bottom of the breach (ft).

7900

brtopwidmax

Maximum width to constrict the top of the breach.

1755

brbottomel

Start of breach elevation (ft). Sensitive to instability. If unstable, set to 1 to 3 ft below the crest elevation.

3.05

weircoef

Weir coefficient

1.5

bratio

Initial breach width to depth ratio.

0.0

breachtime

Time the water surface elevation must sustain before the breach will initiate (hours).

Step 6. Create the breach point#

  1. Identify a good breach location. Choose any desired location.

../_images/Module229.png

  1. Select a breach location. This location can represent a weak point on a dam.

    • Spillways

    • Stilling basins

    • Sag, deformation, or erosion

    • Boreholes

    • Ends points

    • Piezometer measurements

  2. Location is not always important. For large reservoirs flooding is a function of the volume not breach parameters.

  3. It is important to start the breach from the correct side of the levee feature.

  4. Put the breach point on the water side of the levee.

../_images/Module230.png

  1. Click collapse FLO-2D widgets button.

  2. Click the Levees and Breach Editor widget.

  3. Click the create a breach point button.

../_images/number8.png

  1. Click the map where the breach should go and fill the table.

  2. Choose a good location based on engineering judgment.

  3. The data is listed in step 3, 4 and 5.

  4. Click OK to close the table.

../_images/number12.png

  1. Not working? Click Revert Breach Edits button and try again.

../_images/Module231.png

  1. Complete the breach data in the widget.

../_images/Module232.png

Step 7. Export and run the model#

  1. Export the FLO-2D Data files. Click OK.

../_images/Module123.png ../_images/Module233.png

  1. Select the Module 6 Export folder.

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  1. The data is ready to run.

../_images/Module235.png

  1. Correct the paths and click OK to start the simulation.

../_images/Module236.png

Step 8. Review the data#

  1. These are the 3 data files that were created.

  2. Levee.dat needed a Breach switch in Line 1.

  3. Inflow.dat has a “dummy” inflow node. This allows graphics mode to function.

  4. Inflow.dat has the reservoir elevation. When run initiates, FLO-2D will fill the reservoir.

  5. Breach.dat stores the breach variables.

../_images/Module237.png
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