UK EA benchmark 4 (Water Module)

This page reports on the performance of the Tygron Platform's Water Module by means of the UK EA Benchmark Test 4 – Speed of flood propagation over an extended floodplain.

The objective of this test 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.

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 UK Benchmark 4.

Description

This test is designed to simulate the rate of flood wave propagation over a 1,000 x 2,000 m floodplain following a defence 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.

Figure (a): Modelled 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 modelled)
• 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 modelled) 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).

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

• 

  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

• 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 UK 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 Wizard and require configuration through the API.

The locations of the measurement points are:

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	-700

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 (1,000;-2,000).

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:

1. Go to the flooding overlay "Water Level (m)".
2. Select the measuring tool.
3. From the Saved dropdown choose your point of interest.
4. From the Base dropdown select "Surface Elevation (m)".
5. Make sure the Sum box is checked.
6. 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/(m1/3)	0.05
Calc. pref.		Accuracy

Output	Unit	Value
Total volume	m3	282,052
Single cells		81,204
Calc. steps		38,351
Calc. time	s	19

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

Water Module

Tutorials

Overview

Theory

Benchmarks