An application of Delft3D Flexible Mesh

for operational water-level forecasting on the

Northwest European Shelf and North Sea (DCSMv6)

Firmijn Zijl

NGHS Symposium, Delft Software Days

November 5, 2014

Introduction (Acceptance testing)

NGHS acceptance testing

Models considered for acceptance testing

• Official RWS area schematisations for:

• Northwest European Shelf and North Sea

• Rhine-Meuse Entrance

• Meuse River

• Waal River

November 5, 2014

Model Characteristics

Firth of Clyde 2D, tide surge model

Lake Grevelingen 3D, weakly dynamic system with both

temperature and salinity stratification

Neptune

(Singapore coastal

waters)

3D dynamic estuarine system with salinity

and temperature stratification (and

intrusion)

Sea of Marmara 3D, both highly and weakly dynamic parts,

complex combination of salinity and

temperature stratification (CIL)

FSRU Jebel Ali 3D, buoyant plume dispersion

Focus of this presentation

•Development of completely redesigned new generation

Dutch Continental Shelf Model version 6 (DCSMv6).

•Originally developed using the WAQUA module of

SIMONA framework, for numerical modelling of 2D free

surface flows

1) Conversion to D-Flow FM* and comparison to WAQUA

Impact on results

Computational time

2) Model improvements made possible by enhanced

functionality and flexibility of D-Flow FM

E.g. spatially varying resolution to increase

computational speed without loss of

accuracy

November 5, 2014

* D-Flow FM: hydrodynamic simulation engine of Delft3D Flexible Mesh

Operational forecasting in The Netherlands

November 5, 2014

Introduction

The Northwest European Shelf and North Sea

Need for accurate, real-time operational water level forecasting:

•On a daily basis, it is important for port operations and to

ensure maritime safety on busy shipping routes

•For the coastal regions of the Netherlands, it is crucial, since

large areas of the land lie below sea level

•During storm surges, detailed and timely water-level forecasts

provided by an operational storm surge forecasting system are

necessary to support, e.g. the decision for closure of the

movable storm surge barriers in the Eastern Scheldt and the

Rotterdam Waterway

November 5, 2014

Real-time forecasting in The Netherlands

Developments in real-time flood forecasting

in the Netherlands

•Storm Surge Warning Service (SVSD), in close

cooperation with the Royal Netherlands

Meteorological Institute (KNMI), is responsible for

operational forecasts and issuing warnings to coastal

authorities in case of high water threats.

•After the November 2006 All Saints storm it was

decided that further improvements in model

framework were required

• Decision to completely redesign the operational

model

• New generation model is part of a comprehensive

development to upgrade the operational forecasting

system for the North Sea

November 5, 2014

DCSMv6 model development

November 5, 2014

tide + surge surge only

Model setup

November 5, 2014

DCSMv6 (model grid and bathymetry)

Model setup - computational grid

• Increased spatial coverage

• Uniform cell size of 1.5’ (1/40°) in

east-west direction and 1.0’ (1/60°) in

north-south direction (~nautical mile)

• Around 106 active grid cells

Model setup – bathymetry

• Initially based on NOOS gridded

bathymetry data set, supplemented by

ETOPO2

• Changes made during calibration

November 5, 2014

Model setup (boundary forcing)

Model setup - boundary forcing

• Open boundary with 205 sections

• Distinction made between 2 components of the

water level elevation:

(1) Tide, defined in frequency domain (22

constituents)

(2) Surge, as an inverse barometer correction

(IBC) based on time and space varying

pressure fields

November 5, 2014

DCSMv6-ZUNOv4 model setup (meteo forcing)

Model setup - meteo forcing

• Wind speed and air pressure from HIRLAM

model provided (operationally) by KNMI

• Sea surface roughness is calculated using

the Charnock relation (Charnock parameter

0.025)

Model setup - miscellaneous

• Spatially varying manning bed roughness

• Tide Generating Forces (TGF) included

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Calibration approach

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Model calibration

Calibration and validation using tide gauge data at >120 locations

Green dots: radar altimeter cross-over locations

Red dots: in-situ tide-gauge locations

November 5, 2014

DCSMv6 (against satelite altimeter data) M

2 A

mplit

ude

M2 P

hase

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DCSMv6 Model Development

OpenDA-DUD experiment setup and

parameters

•Reduction of uncertainty in bottom friction

coefficient and bathymetry

•Multiple optimization runs, with increasing length

and number of parameters

•Final experiment (DCSMv6)

• 200 control parameters, 12 months, ~100

observations locations

• To achieve desired accuracy many interactions

become important (in terms of processes and

geographically)

November 5, 2014

Results

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Dutch coastal stations

RMSE

(tide)

RMSE

(surge)

RMSE

(total)

RMSE

(high water)

RMSE

(low water)

DCSMv5 10.7 7.7 13.1 11.3 11.0

DCSMv6 (WAQUA) 4.1 5.9 7.2 6.6 7.1

DCSMv6 (D-Flow FM) 4.9 6.0 7.8 6.8 7.1

Goodness-of-Fit (in cm) - 13 Dutch coastal stations - entire year of 2007)

November 5, 2014

November 5, 2014

DCSMv6 model comparison

Red: Measurement

Black: Computation

Blue: Residual

Waqua D-Flow FM

Tide representation in the frequency domain

RMS(ΔA) RMS(ΔG) RMS(VD)

Q1 0.4 0.4 6.0 8.4 0.5 0.6

O1 0.2 0.4 2.0 2.0 0.5 0.6

P1 0.8 0.7 5.2 5.7 0.9 0.8

K1 0.2 0.2 2.4 1.6 0.4 0.3

N2 0.3 0.4 1.3 2.6 0.5 0.8

M2 1.1 2.3 1.0 1.5 1.9 3.4

S2 1.1 0.6 1.0 1.7 1.2 1.0

K2 0.8 0.5 1.6 3.6 0.8 0.7

M4 0.6 1.0 8.7 12.3 1.5 2.3

M6 0.6 0.7 11.5 11.2 1.3 1.4

A: amplitude in cm, G: phase in °, VD: vector difference in cm

Based on 13 Dutch coastal stations

November 5, 2014

Tide representation in the frequency domain

M2 amplitude and phase errors along Dutch coast

WAQUA D-Flow FM

November 5, 2014

November 5, 2014

DCSMv6-ZUNOv4 (Dutch estuaries and Wadden Sea)

Based on 16 stations in Dutch estuaries en Wadden Sea

RMSE

(tide)

RMSE

(surge)

RMSE

(total)

DCSMv6 (WAQUA) 7.1 7.0 9.9

DCSMv6 (D-Flow FM) 9.9 7.1 12.2

Consistency in depth

interpolation options is

crucial to achieve similar

results

Conclusions

November 5, 2014

Computational time

Comparison of computational time

•Both models use a computational

time step of 2 minutes (determined

with convergence tests)

•Performance tested on Deltares

cluster (quad-core machines)

•No use made of enhanced flexibility

of D-Flow FM

•Speed-up is hardware dependent

•More effort required to improve

scaling efficiency

November 5, 2014

number of nodes (with 4 cores each)

co

mp

. tim

e [m

in p

er

da

y]

number of nodes (with 4 cores each)

sp

ee

d-u

p [-]

Summary and conclusions

•Completely redesigned, new generation Dutch Continental Shelf Model version 6

(DCSMv6) has been developed

• Year-long simulations show excellent agreement with (shelf-wide) measurements

• Running the model in D-Flow FM reduces the water level representation accuracy

• It is expected that the D-Flow FM accuracy can be improved with limited re-

calibration

• For this application D-Flow FM is twice as slow as Simona-Waqua (on one node)

• Enhanced flexibility of D-Flow FM has not been used, but will save

computational time

•Scalability of D-Flow FM is rightly getting more attention (hardware dependent)

Next step (1): make use of enhanced flexibility of D-Flow FM to reduce number of

cells and increase time step by avoiding unnecessary high resolution in the deeper

areas off the shelf

Next step (2): Acceptance testing with different models, as results are application

dependent

November 5, 2014

DCSMv6

Questions?

November 5, 2014