Flood consequence assessment: flood model checklist

If you're providing a hydraulic model to support your Flood Consequence Assessment (FCA) you will need to include a flood model checklist using our flood model checklist template 

The checklist asks a series of questions that should help demonstrate that the flood model has been built appropriately and the correct output has been created. A summary of the flood model checklist is provided below with more information and instructions contained within the template.

Modelling approach

1.0    General

1.1    Has there been contact with NRW prior to modelling? If yes, please give details.
1.2    Is there an NRW model at the site? If no, go to 1.4.
1.3    Was the NRW model used and licenced?
1.4    Was any other data requested from NRW and used in the model?
1.5    Has the Welsh Government Climate Change guidance been adopted?
1.6    Is there any historical flood data for the area? If yes, model validation and calibration is reviewed in more detail in the MODEL CONFIDENCE section.

2.0     Methodology and reporting

2.1    New build models: does the report contain sufficient details on model build, decisions and assumptions made?
2.2    NRW model: have all changes made to the original NRW model been noted and sufficiently documented in the report?
2.3    Is there evidence of site visit(s)?
2.4    Are the objectives of the analysis clearly set out?
2.5    Is the analysis appropriate to meet these objectives?

3.0    Fluvial/ Hydrology

3.1    Has a new hydrology assessment been undertaken?
3.2    Has the hydrology Flood Estimate Calculation (FEC) Record been completed?
3.3    Was the flood estimate calculation record agreed with NRW before you began any detailed hydraulic modelling?
3.4    Do the NRW hydrology team accept the hydrology?

4.0    Tidal inflows

4.1    Has the tidal boundary been derived in accordance with the ‘Coastal flood boundary conditions for the UK: update 2018’?
4.2    Have the calculations been provided?
4.3    Is there wave overtopping? If so, have the calculations been provided and are they suitable?

5.0    Survey

5.1    Is data source stated?
5.2    Is method stated?
5.3    Is survey current? If no see 5.4. If yes, has the date been provided?
5.4    Has check survey been performed?
5.5    Are E stations listed?
5.6    Has sufficient data been collected?
5.7    Are levels to Ordnance Datum?
5.8    Is data in electronic format?
5.9    Is data georeferenced? If not provide location plan.
5.10    Is LiDAR data current? If yes, has the date been provided?
5.11    Is the resolution of the LiDAR suitable?
5.12    Does the LiDAR used pick up all recent topographical changes in the model extent that could influence the model results?

Hydraulic Model Build

6.0    General
6.1    Is the model the correct type?
6.2    Has the recommended data management structure for the software package been used?
6.3    Have any non-default settings been used  for the 1D & 2D components?
6.4    Is model timestep appropriate?
6.5    Do the reach lengths match survey data and/or 2D representation?
6.6    Is the model run time sufficient to ensure the water levels have peaked across the model domain?
6.7    Have waterbodies been considered and modelled appropriately?

7.0    Inflows and boundary conditions

7.1    Are the inflow locations in the correct place within the model domain?
7.2    Are the inflows the same as those stated in the report?
7.3    Has the appropriate range of flows/tides been modelled?
7.4    Are the upstream and downstream boundary types appropriate?
7.5    Does model extend far enough upstream and downstream?
7.6    Tidal only - How has the wave overtopping been applied? Is it appropriate?
7.7    Pluvial - How has rainfall been applied? Is it appropriate?
7.8    Has infiltration been considered? If so, how and is it appropriate?

8.0    1D model

8.1    Are the initial conditions appropriate?
8.2    Are model cross-sections widths appropriate?
8.3    Is model cross-section spacing appropriate?
8.4    Have interpolated sections been kept to a minimum?
8.5    Are 1D roughness (Manning's) values sensible?
8.6    Are structures modelled appropriately?
8.7    Does conveyance look smooth in cross section plots?
8.8    Have panel markers and floodplain markers been used appropriately?

9.0    2D model

9.1    Is grid/mesh size and orientation appropriate?
9.2    Is grid representative of the DTM?
9.3    Are the initial conditions appropriate?
9.4    Is the model domain appropriate?
9.5    Have buildings been represented appropriately?
9.6    Is the Manning roughness representation adequate?
9.7    Are structures and floodplain features modelled appropriately?

10.0    1D-2D linked model

10.1    Does the 1D cross section width and levels match the 2D representation?
10.2    How have the 1D/2D models been coupled, is it appropriate?
10.3    Is the digitisation of the links acceptable?
10.4    Have 1D outputs been represented appropriately in the 2D domain?
10.5    Have any default link parameters been changed (i.e. to improve stability)?

Model Confidence

11.0    General/ House keeping

11.1    Does the model run?
11.2    Have all superseded files and results been removed?
11.3    Are model run-time log/check files included?
11.4    Has a full set of 1D and 2D raw and processed results been provided?
11.5    Do the model and outputs pass a reality check?
11.6    Do the model flows reconcile with the hydrology flow estimates as the downstream boundary or area of interest?

12    Stability

12.1    Are there any model stability issues?
12.2    Have stability patches been applied, if so are they appropriate?
12.3    Have Errors / Comments / Warnings flags been addressed / minimised?
12.4    Has the volume across the model been checked with PO lines?

13    Verification

13.1    Have the model outputs been verified against a recorded extent and / or anecdotal information, such as flow routes, wrack marks, inundation times etc?
13.2    Are the outputs/results realistic?

14    Calibration

14.1    Is there suitable data available for calibration and has it been used?
14.2    Have calibration runs been undertaken?
14.3    Is the data used for model calibration appropriate?
14.4    Have any changes been made to the model during this process and are they appropriate and realistic?
14.5    How many events have been used during calibration and are they suitable to use?
14.6    Does the model calibrate?
14.7     Are the simulated hydrograph peaks and shape reasonably similar to the recorded peaks?

15    Sensitivity

15.1    Have appropriate sensitivity tests been run?
15.2    Have appropriate model parameters been chosen for sensitivity testing?
15.3    Do the results of the tests show the model to be significantly sensitive to certain parameters?

16    Uncertainty

16.1    Have the model limitations and assumptions been justified?
16.2    Have uncertainty limits for model results (+/- mm) been presented? How were they derived and does this seem sensible?
16.3    Has a freeboard allowances been considered? Is it reasonable in the context of the uncertainty limits?
16.4    Was an explicit statement of any concerns about the accuracy of the model or its ability to represent reality provided?

Flood Consequence Assessment

17    General

17.1    Have both the 'As Existing' (baseline) and 'With Development' (proposed scheme) models been submitted?
17.2    Are the proposed development plans provided and of sufficient detail?

18    Proposed Development Model

18.1    Has the topography of the proposed development been represented in the model with sufficient detail?
18.2    Has the Manning's roughness been updated for the proposed model?

19    Site Specific Model Requirements

19.1    Has a blockage assessment been undertaken? (if no, move to 19.4)
19.2    Has the blockage/s been applied correctly to the model?
19.3    Do the blockages applied in the model match those documented in the FCA?
19.4    Has a breach assessment been undertaken? (if no, move to section 20)
19.5    Has the breach/es been applied correctly to the model?
19.6    Do the breach/es applied in the model match those documented in the FCA?

20    Mitigation Modelling

20.1    Are mitigation option/s proposed as part of the development scheme? If no, move to section 21.
20.2    Is there sufficient information detailing the proposed option(s)?
20.3    Have these been applied to the model correctly?
20.4    Has an assessment of their impact been undertaken for all events?

21    FCA Outputs

21.1    Have third party impacts been displayed correctly?
21.2    Is impact off-site less than or equal to 5mm? If not, is the impact justified sufficiently?
21.3    Are mapped outlines supplied?
21.4    Do the mapped outputs match the raw results?

Flood Map Challenge

22    Intellectual Property Rights (IPR)
22.1    Is the model intended to be used to update NRW mapping or flood risk products?
22.2    Has a change note form been completed?
22.3    Has the appropriate IPR been granted to NRW?
22.4    Are details provided to enable running of the model (i.e. naming convention and run switches)?

23    General

23.1    Is the area / layer being challenged clearly communicated?
23.2    Does the model offer new evidence which improves on the existing standard of evidence?
23.3    Can the upstream and downstream extents tie into the national flood maps?

24    Events and Scenarios

24.1    Have the correct events and scenarios been simulated and outputs provided?
24.2    Defended Model - Does the defended model include appropriate defences only?
24.3    Undefended Model - Have all Risk Management Authority, private and defacto (informal) defences been removed from the model?