UK EA benchmark 4 (Water Module)

This benchmark performs the UK EA benchmark Test 4 – Speed of flood propagation over an extended floodplain using the Water Module of the Tygron Platform.

The objective of this benchmark is to assess the package’s ability to simulate the celerity of propagation of a flood wave and predict transient velocities and depths at the leading edge of the advancing flood front. It is relevant to fluvial and coastal inundation resulting from breached embankments.^[1]

A copy of this test project is made available to everyone, providing hands-on insights to those interested. The project can be found on the LTS server under the name UKEA benchmark 4. This is covered in more detail in this section.

Animation of the test result for case 4, generated by the Tygron Platform. Map dimensions = 1,000 x 2,000 m. Grid-cell size = 5 m.

Description

This test is designed to simulate the rate of flood wave propagation over a 1,000 x 2,000 m floodplain following a defense failure (Fig. (a)). The floodplain surface is horizontal, at datum (= 0 m). One inflow boundary condition will be used, simulating the failure of an embankment by breaching or overtopping, with a peak flow of 20 m³/s and time base of ~6 h. The boundary condition is applied along a 20-m line in the middle of the western side of the floodplain.^[1]

Figure (a): Modeled domain and the locations of the 20-m line of inflow, 6 output points, and the aimed for 0.1-m and 0.2-m contour lines at t = 1 h (dashed) and t = 3 h (solid), respectively.

Figure (b): Hydrograph applied as inflow boundary condition.

Boundary and initial condition

Inflow boundary condition as shown in Fig. (b)
All other boundaries are closed
Initial condition: dry bed

Parameter values

Manning’s n: 0.05 (uniform)
Model grid resolution (m): 5 (or ~80,000 nodes in the area modeled)
Simulated time (h): 5

Required output

Point ID	X	Y
1	50	1,000
2	100	1,000
3	200	1,000
4	300	1,000
5	400	1,000
6	300	1,300

Software package used: version and numerical scheme
Specification of hardware used to undertake the simulation: processor type and speed, RAM
Minimum recommended hardware specification for a simulation of this type
Time increment used, grid resolution (or number of nodes in area modeled) and total simulation time to specified time of end
Raster grids (or TIN) at the model resolution consisting of:
- Depths and at t = 30 min, 1 h, 2 h, 3 h and 4 h
- Velocities (scalar) at t = 30 min, 1 h, 2 h, 3 h and 4 h
Plots of velocity and water elevation v. time (suggested output frequency: 20 s) at the 6 locations represented in Fig. (a) and provided as part of dataset

Dataset content

Upstream boundary condition table (inflow v. time). Filename: Test4BC.csv
Location of output points. Filename: Test4Output.csv

The model geometry is as specified in Section 2. No DEM is provided, as the surface elevation is level at datum (= 0 m).^[1]

Technical setup

Figure 1. The relative positions of the measurement points used in this test.

Flat surface
Grid-cell size (m): 5
Area size (m): 1,010 x 2,010 (required domain of 1,000 x 2,000 + 5-m border)
The measurement points were positioned correctly (see Fig. 1)

In order to regulate the boundary discharge according the hydrograph (Fig. 2), 2 inlets were implemented. Both inlets occupied one grid cell, one of these located above and the other below the green center line (Fig. 3). The inlets were configured as follows:

External area (m²): 1,000,000,000 (default)
Water level (m): 1 (default)
Threshold (m): none (default)
Inlet Q (m):

Figure 2. Hydrograph displaying the implemented individual and combined inlet fluxes.

Figure 3. Positions of the inlet cells (red squares) with respect to the center line of measurement (green).

Results

Stats

Software package used: Tygron Platform
Numerical scheme: FV (Kurganov, Bollerman, Horvath)
Specification of hardware used to undertake the simulation:
- Processor: Intel Xeon @2.10GHz x 8
- RAM (GB): 62.8
- GPU: 2x NVidia 1,080
- Operating system: Linux 4.13
Time increment used: adaptive
Grid resolution (m): 5
Calculation time (s): 29 (for 900 timeframes)
Object flow (m³/s): 283,723.8
Remaining water volume (m³/s): 283,606.9

Raster grids (or TIN) at the model resolution for water level and flow velocity

Contours of inundation extent (>= 0.15 m depth)

t = 30 min
t = 1 h
t = 2 h
t = 3 h
t = 4 h

Results of other packages for t = 1 h and 3 h.

Cross sections

Water level across center line at t = 1 h.
Water level across center line at t = 1 h for other packages.

Flow velocity across center line at t = 1 h.
Flow velocity across center line at t = 1 h for other packages.

Time series of water level and flow velocity

Water level at Point 1.
Water level at Point 1 (others).

Flow velocity at Point 1.
Flow velocity at Point 1 (others).

Water level at Point 2.

Flow velocity at Point 2.

Water level at Point 3.
Water level at Point 3 (others).

Flow velocity at Point 3.
Flow velocity at Point 3 (others).

Water level at Point 4.

Flow velocity at Point 4.

Water level at Point 5.
Water level at Point 5 (others).

Flow velocity at Point 5.
Flow velocity at Point 5 (others).

Water level at Point 6.
Water level at Point 6 (others).

Flow velocity at Point 6.
Flow velocity at Point 6 (others).

Notes

Test results of Point 2 and 4 for the other packages were not provided.
The stepwise behavior seen in the velocity profiles can be related to the definition of the inlet inflow, which is also stepwise.

Public test project

A copy of this test project is made available to everyone, providing hands-on insights to those interested. The project can be found on the LTS server under the name UKEA benchmark 4. In this project the discussed benchmark test is reproduced, based on a map size of 1,010 m x 2,010 m to compensate for the 5-m border cells. These special map dimensions are generally not selectable in the New Project Wizard and require configuration through the API.

Measurement points

The locations of the measurement points are:

Point ID	X	Y
1	55	-1,005
2	105	-1,005
3	205	-1,005
4	305	-1,005
5	405	-1,005
6	305	-705

Note that the coordinate system in this project differs from the one used during the actual benchmark testing as shown in Fig. (a). For the above listed points the center (0,0) is located at the top-left corner instead of the bottom-left, hence will the bottom-right corner have coordinates (1,010;-2,010).

Water level relative to datum

The time series of a fixed measurement point can be obtained as follows:

How to obtain water levels relative to datum:

Go to the flooding overlay "Water Level (m)".
Select the measuring tool.
From the Saved dropdown choose your point of interest.
From the Base dropdown select "Surface Elevation (m)".
Make sure the Sum box is checked.
Select Fit Graph to zoom in on the relevant part of the plot.

Settings & output

Setting	Unit	Value
GRAVITY	m/s²	9.80665
QUAD_CELL	Boolean	0
Open land	m²	14,496,160
Surface elevation	m	1
Manning's n	s/(m^1/3)	0.05
Calc. pref.		Accuracy

Output	Unit	Value
Total volume	m³	282,057
Water balance error	m³	-159 (0%)
Single cells		81,204
Calc. steps		49,008
Calc. time	s	22

Note that these output values may deviate slightly from those of the initial testing phase (i.e. not the public test project), since there is a substantial time gap between when the two projects were set up, during which several changes have been made to the engine.

References

↑ ^1.0 ^1.1 ^1.2 Néelz, S., & Pender, G. (2013). Benchmarking the latest generation of 2D hydraulic modelling packages. Report: SC120002. Environment Agency, Horison House, Deanery Road, Bristol, BS1 9AH. ISBN: 978-1-84911-306-9. Retrieved from: https://www.gov.uk/government/publications/benchmarking-the-latest-generation-of-2d-hydraulic-flood-modelling-packages