Comparing flood mapping performances of 1D/2D hydraulic … · WFIUH) (vs rational method and triangular hydrograph) for evaluating hydrologic design scenario • DEM-based flow direction/path

Association of State Floodplain ManagersSeattle, WA (USA) – June 1-6, 2014

Comparing flood mapping performances of 1D/2D hydraulic modelsusing DEMs for representing the floodplain and channel morphology

Comparing flood mapping performances of 1D/2D hydraulic models using DEMs for representing the floodplain and

channel morphology

Model Comparison Session @ 2014 ASFPM ConferenceSeattle, WA (USA) - June 5th, 2014

Fernando Nardi, Antonio AnnisUniversity for Foreigners of Perugia (Italy)Alfred Kalyanapu, Nowfel Mahmud BhuyianTennessee Technological University (USA)Mauro NalessoIDRAN Ingegneria e Tecnologia Srl (Italy)



• The Tiber river basin case study (city of Rome)• Major river systems• Small ungauged tributaries

• Technical specifications for flood modelling and mapping

• Hydrology• Topography• Mapping: floodplain vs flood map• 1D vs 2D flood modelling

Outlines



Tiber river case study

Area ~. 17,000 km2

Max. Elev ~ 1268 m aslMean Annual precipitation ~ 1200 mm



City of Rome



City of RomeTiber river within the urban area and the “walls” (levees)

Coastal floodplain

100 yrsUrban flood map




City of Rome

Aniene river basin (approx. 1,600 km2)

Main tributary of the Tiber river in the urban area





City of Rome

HYDROGEOMORPHIC FLOODPLAIN

Hydrologic-Hydraulic

flood maps



City of Rome Urban river system



Nov. 2012 flood event



200 yrs flood mapping

2D flood model simulations



200 yrs flood mapping

2D flood model simulations

Coastal area

Urban walls overtopping

500

1000

1500

2000

2500

3000

3500

4000

0 50 100 150 200 250 300

Po

rta

ta [

mcs]

Tempo [ore]

TR 100

TR 200

TR 500

1D/2Driver model

2DFloodplainmodel 10m



100-200 yrs flood mapping

2D flood model simulations Coastal area



0

5

10

15

20

25

30

35

40

45

0 5000 10000 15000 20000 25000 30000 35000

Quo

ta a

ltim

etri

ca [m

slm

]

Progressiva metrica [m]

Profilo fondo alveo TR50 TR100 TR200

Aniene river 200 yrs flood mapping



Aniene river 200 yrs flood mapping



2D flood modelling for major river systems

• Enforcing predefined flood scenario (hydrology and eventually hydraulics from previous 1D study)

• Understanding flood dynamics of major river systems interacting with tributaries and levee-protected (floodplain) zones

• Spatially distributed flow depths and velocities for regulatory (urban planning) purposes



Tributaries in urban area• Recent floods within the

city have been caused by minor basins

• Significant impact of urbanization

• Lack of previous hydrologic and hydraulic studies



Flood modelling domain for tributaries

• 13 small ungauged riverbasins

• basin area range 30-150 km2

(tot. 1093 km2)• River reach average length:

approx. 20 km



13 minor basin tributaries

Channel lengthTot. 220 km

600+ river/street intersections

Flood modelling domain for tributaries



Technical specifications for 2D flood model

- Lack of:- technical guidelines for 2D flood modelling in small gauged

basins- validation data

- Need to:- Compare/consider 1D modelling (guidelines, results, …)- 2D modelling for the complex fluvial-urban system

processes and features- Optimizing topographic data resources



Hydrology

• GIS-based geomorphic IUH (GIUH and WFIUH) (vs rational method and triangular hydrograph) for evaluating hydrologic design scenario

• DEM-based flow direction/path processing



Hydrology

• Basin discretization for subbasin design hydrology characterization• Compensate the impact of flood routing and volume losses for safely

estimating flood hazard



Topography• LIDAR, UAV and Laser Scanner for highly

detailed DTM and DSM• Field survey of bridges and culverts• Simplified fluvial bathymetry



TopographyGIS data integration with existing and/or simplified bathymetry



Mapping

Major and minor river system flood hazard integrated mapping



Mapping

Major and minor river system flood hazard integrated mapping



2D flood maps

Hazard map



2D flood maps

Flow depths



2D flood maps

Flow velocity



Floodplain map



Floodplain vs flood map



Floodplain vs flood map



1D vs 2D

• Large flat areas with minor channelization

• Leading impact of urban features (bridges, culverts, …) on flood dynamics

• Urbanized floodplain characterizing unsteady 2D extra-channel flows



1D vs 2D






1D vs 2D






1D vs 2D• significant floodplain

depths• channel/flow area/process

is not dominant• detailed hydrologic-

hydraulic modelling of bridges/culverts

• Can we use simplified DEM-based topography with a 2D model?



Discussion• No, we can’t use DEM-based 2D model

• Regulatory and specification issues• Validation issue

• BUT, we can use 1D model for flood maps produced by postprocessing/interpreting extra channel flow process



Ongoing/Future work

• Comparing/validating 1D flood model with different bathymetric characterization (ASCE Journal of Hydrologic engineering, in press)

• Using 2D model for US and Aniene basin (ongoing)



Ongoing/Future work

• Using GIS modelling for combining worst case scenarios by integrating 1D and 2D hydraulic model results

• Validation of hydrology (flow gauge) and hydraulics/mapping (surveyed flood depths/areas)

• Providing accurate, reliable and easy-to-interpret information for regulatory flood map/engineering standard updates



Thanks for your attention

[email protected]

@fnardi

Documents

Comparing flood mapping performances of 1D/2D hydraulic … · WFIUH) (vs rational method and triangular hydrograph) for evaluating hydrologic design scenario • DEM-based flow direction/path