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.

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	300	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. Setup of case 4 used by the Tygron Platform

• 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
• Water level (m): 1
• Threshold (m): none
• Inlet Q (m):

Figure 2. Inlet influx graph used by the Tygron Platform

Figure 3. Inlet positions.

Results

• 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 62.8 GiB,
  • GPU: 2x NVidia 1080
  • Operating system: Linux 4.13
• Time increment used: adaptive:
• Grid resolution: 5 m.
• Simulation time: 29 seconds for 900 timeframes
• Inlet q M3: 283723.8 m³
• Remaining volume water: 283606.9 m³

Raster grids (or TIN) at the model resolution consisting of waterlevels and velocities

Contours

• 

  Contour 30 minutes.
• 

  Contour 1 hour.
• 

  Contour 2 hours.
• 

  Contour 3 hours.
• 

  Contour 4 hours.


• 

  Contour 1 and 3 hours of others.

Cross sections

• 

  Waterlevel cross-section after 1 hour.
• 

  Waterlevel cross-section others after 1 hour.


• 

  Velocity cross-section after 1 hour.
• 

  Velocity cross-section others after 1 hour.

Plots of velocity and water elevation versus time

• 

  Waterlevel point 1.
• 

  Waterlevel point 1 others.


• 

  Velocity point 1.
• 

  Velocity point 1 others.


• 

  Waterlevel point 2.


• 

  Velocity point 2.


• 

  Waterlevel point 3.
• 

  Waterlevel point 3 others.


• 

  Velocity point 3.
• 

  Velocity point 3 others.


• 

  Waterlevel point 4.


• 

  Velocity point 4.


• 

  Waterlevel point 5.
• 

  Waterlevel point 5 others.


• 

  Velocity point 5.
• 

  Velocity point 5 others.


• 

  Waterlevel point 6.
• 

  Waterlevel point 6 others.


• 

  Velocity point 6.
• 

  Velocity point 6 others.

Notes

• The steps seen in the velocity profile can be related to the definition of the inlet inflow, which is also in steps.