Connecting 1D and 2D Domains

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1 Connecting 1D and 2D Domains

2 XP Solutions has a long history of Providing original, high-performing software solutions Leading the industry in customer service and support Educating our customers to be more successful in their work.

12 years of water resources industry experience, including

3 Our Presenter Venu Kandiah, PhD, P.E. Senior Water Resources Engineer With XP Solutions since July years of water resources industry experience, including experience as an engineering consultant and in a public utility Experience in modeling, planning and design

4 Connecting 1D and 2D Domains Webinar Overview Introduction to 1D/2D Modeling Setup & Best Practices for Connecting 1D/2D Domains Common Errors and Troubleshooting 1D/2D Domain Flow Exchanges

5 Introduction to 1D/2D Modeling

each time step Links Uniform throughout (open channel,

6 1-Dimensional Models Vertical and lateral flow components are neglected 1D flow assumption Nodes HGL calculated for each time step Links Uniform throughout (open channel, pipe cross section) Q, V, A are calculated for each time step

7 1-Dimensional Models Advantages Easy to build; model large areas easily; lower computational effort Less complicated theory Well accepted engineering practice Disadvantages Cannot model shallow overland flows correctly - pattern is essentially 2D During high flow events potential storage in floodplains or urban landscapes are not properly simulated Requires a lot of engineering judgment and is therefore subject to the skill of the modeler

8 2-Dimensional Models Flow in both X and Y directions a 2-D plane Square grids represent topography. Grids contain elevations, land use and other hydraulic parameters Continuity and momentum equations solved for each grid

9 2-Dimensional Models Advantages Easy to build overland 2 dimensional flood flow models from surface data (Urban flood flow patterns are also 2 dimensional flows) Automatically model the flood flow storage effects Directly create flood inundation maps Less engineering judgment required Disadvantages Precise and dense survey data is desired More computational power and time required Difficult to model very large areas with small cells Tradeoff in accuracy of representation and cell size Relatively new approach; still being developed; small user community

10 Limitations of 2D Representation Cross-Section Elevation Poor channel represented in 2D model 39.0 Actual channel cross-section True Distance

11 Coupled 1D/2D Models 1D models useful for simulating underground piped flows cross drainage culverts (rectangular, circular, other shapes) open channel flow 2D models useful for simulating floodplains complex overland flows (urban flooding) wide watercourses

12 What are typical applications for which you currently use, or plan to use, 2D modeling? Floodplains Urban Areas Coastal Areas Wetlands Dam Break Poll

13 Connecting 1D and 2D Domains

14 Coupled 1D/2D Model Applications 2D Overland Flow 1D Channel Flow Junction/Manhole/Pit 2D Overbank Flow 1D Pipe Flow Channel in 1D and Floodplain in 2D Pipe in 1D and Developed Urban Areas in 2D

15 Setup and Best Practices

16 Recommended Workflow 1. Develop a working1d Model 2. Determine limits of 1D and 2D models and linkages a. Open channel modeled in 1D, surface area of open channel removed from 2D b. Pond modeled as 1D node, pond footprint removed as 2D 3. 2D Model Construction a. Define 2D Grid and Surface b. Define 2D inactive areas c. Define 1D/2D connections for channels and manholes d. Define Landuse e. Define Boundary Conditions f. Set Job Control

Connecting Channels in 1D/2D 1D/2D Connection Line 1D/2D Interface Line Active 2D Area Define Inactive 2D Area Polygon and Define 1D/2D Interface Lines Digitize along top of bank 2D Water level

17 Connecting Channels in 1D/2D 1D/2D Connection Line 1D/2D Interface Line Active 2D Area Define Inactive 2D Area Polygon and Define 1D/2D Interface Lines Digitize along top of bank 2D Water level interpolated using water levels at 1D nodes 1D Node (1D water level computed) Inactive 2D Area Polygon Inactive cells 1D Link Connect 1D nodes to 1D/2D Interface using 1D/2D Connection Lines Digitize perpendicular to flow 1D water level is translated to the 2D domain along the 1D/2D interface Level interpolated between neighbouring 1D connections

18 Connecting Manholes in 1D/2D Default rating curve for overland flow capture to the node. This can be modified if the user has another one. The outflow from node to 2D domain is computed by the mass balance at the node.

19 Common Errors and Troubleshooting

20 Modeling Culverts Culvert modeled in 1D Water levels in 2D cells on either end of culvert define the gradient across culvert Flow through culvert is applied as a sink/source to 2D cells The 1D/2D interface (and connection) should reflect the size of the structure Use a point if less than 2D cell size Use line if greater than 2D cell size

21 Modeling Channels 1D cross-section frequency is important Too frequent may cause instabilities Too few and the 1D water surface profile will be poor, causing poor 1D/2D linking Wrong Cross Sections too frequent

22 Modeling Channels 1D cross-section frequency is important Too frequent may cause instabilities Too few and the 1D water surface profile will be poor, causing poor 1D/2D linking Correct Spaced ~ 5-20 Cells

23 Channel Setup Errors This area will contain no flow If the spill crest is too low 1D Nodes are not high enough to allow 1D flow to rise to a flood level (creates pressure flow in the river)

24 Channel Setup Errors Need node spill crests higher than expected flood level and VERT_WALLS activated

25 1D/2D Interface Line Correction Tool Locate the 1D/2D Interface along the top of bank Elevation in 1D does not match well with the 2D grid Ability to View and Automatically Correct Interface / 2D cell elevations along top of bank

26 Manhole Setup Errors Problem 2D Cell Elev > 1D Node Spill Crest Solution Automatic Fix 2D Job Control -> Levels Automatically lower 2D Cell to 1D Node Spill Crest

27 Manhole Setup Errors Problem 1D Node Spill Crest > 2D Cell Level Smokestack water in 2D has to rise to be captured in node Solution Tools -> Generate Ground Elevations from TIN Fix Manually

28 1D/2D Flow Exchanges

29 1D Log Table E19 1D/2D Models Flow Exchange

30 1D Log Table E20 1D/2D Models Flow Exchange

31 1D/2D Models Inflow Hydrographs 2D Job Control -> Enable Check Files -> Advanced Settings, Enable Parameter Write X1D Check Files, Value ON

32 Summary Coupled 1D/2D models provide a sound approach for modeling systems where a combination of both 1D and 2D flows are expected 1D/2D model development requires a good understanding of which components can be modeled in each domain and how they are connected Be aware of inaccuracies that 2D cell discretization can introduce (elevations, hydraulic characteristics) 1D/2D boundaries and links need to be verified

33 Q & A

com Contact XP Solutions Americas: +1 888 554 5022 amsales@xpsolutions.

34 Questions? Comments? Thank you for your time and interest! Connecting 1D and 2D Domains By Venu Kandiah Contact XP Solutions Americas: Asia Pacific: ausales@xpsolutions.com EMEA: uksales@xpsolutions.com

Gavin Fields Senior Water Resources Engineer XP Solutions

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