Two-Dimensional Hydraulic Modeling Uses and Advantages

Two-Dimensional Hydraulic Modeling
Uses and Advantages
Chris Doherty, PE, CFM
Lance McLeod, PE,CFM

2D Hydraulic Modeling: Introduction
• What is 2D modeling?
How is it different from 1D modeling?
• What are the benefits of using 2D modeling?
What situations are better suited for 2D?
• What are the limitations of using 2D modeling?
• Example Projects –
Grand Parkway Segment E
Brazos River Memorial Park
Brown & Gay Engineers, Inc.

Grand Parkway
Background
• First proposed in 1965
• 170-mile loop in 7
counties
• 11 segments
• $3.7 billion total cost
• 2 segments complete
(D and I-2)

Grand Parkway (SH99) Background: Segment E
Brown & Gay Engineers, Inc.

Grand Parkway (SH99) Background: Segment E
• 14-mile rural freeway section
from Franz Road (south) to
US 290 (north)
• 11.5 miles without frontage
roads
• Four-lane section expandable
to eight lanes in the future
• Twelve at-grade intersection
crossings (roadway bridges)
• Four stream bridges
• Five tributary stream
cross culverts
• Two major watersheds
Brown & Gay Engineers, Inc.

Segment E: Drainage Background
GRAND PARKWAY SEGMENT E
DRAINAGE DESIGN PARAMETERS
Road-side system
conveyance
Runoff detention
Cross Culverts
Stream Bridges
Floodplain mitigation
10% (10-yr) storm event for ROW plus 150-development
strip
10% (10-yr) and 1% (100-yr) storm events for ROW only
2% (50-yr) capacity with 1% (100-yr) conveyance below
road
Floodway span (minimum) with no impact to stream
Full mitigation for all 1% (100-yr) volumetric and
conveyance losses
Brown & Gay Engineers, Inc.

Segment E: Watershed Conditions
• Rural agricultural area with little
development
• Soils are predominantly clay to
sandy loam
• Ground topography is generally flat
• Overland runoff travels northwest
to southeast
• Cypress Creek has a history of
overflows contributing runoff to the
Addicks watershed
• Segment E is situated
perpendicular to watershed sheet
flows
Cypress Creek
Cypress Overflow
Langham Creek
South Mayde Creek
Segment E
Bear Creek
Brown & Gay Engineers, Inc.

Segment E: Cypress Creek Overflow
Overflow
Cypress Creek
Brown & Gay Engineers, Inc.

Segment E: 2D Analysis Rationale
• 1D models for floodplains assumes that flow is parallel to
main channels – there is a significant overland flow
• 2D model is better for modeling divergent flow paths and
design with overland flow
• 2D analysis was chosen to evaluate these overflow
conditions in relation to the Grand Parkway and
provide the basis for pass-through recommendations to
mitigate potential adverse impacts
Brown & Gay Engineers, Inc.

Segment E: Pass-Through Culvert Concept
Existing Condition:
Brown & Gay Engineers, Inc.

Segment E: Pass-Through Culvert Concept
Proposed Condition – with Impact:
Brown & Gay Engineers, Inc.

Segment E: Pass-Through Culvert Concept
Proposed Condition – with Pass-Through Culvert:
Brown & Gay Engineers, Inc.

2D Analysis: Model Software Selection
Public Domain
• FESWMS 2DH (USGS) *
• RMA2 (USACE-WES) *
• SRH2D (USBR)
Private License
• SMS (Aquaveo)
• MIKE Flood (DHI) *
• FLO-2D *
• Delft-1D2D (Sobek)
• InfoWorks RS / ICM (MWH Soft)
• XP-2D (XP Software)
* Meets minimum NFIP criteria
Brown & Gay Engineers, Inc.

2D Analysis: Model Elements
• Logical Zone Boundaries
• Overall Study Area
• Channel flow zone
• Overland flow zone
• Physical / Material changes (roughness)
• Elevation Data Input
• GIS and SMS pre-processing
• LiDAR data
• HEC-RAS cross section data
Brown & Gay Engineers, Inc.

Segment E 2D Analysis: Study Area
Cypress Creek
Segment E
Study Area =
37,767 Acres
(59 sq. miles)
Langham Creek
Bear Creek
South Mayde Creek
Brown & Gay Engineers, Inc.

Segment E 2D Analysis: Methodology
Brown & Gay Engineers, Inc.

2D Analysis: Model Elements
• Hydrologic Input
• Define Inflow Locations
• At upstream flow boundaries
• Within the study area
• Boundary Conditions
• Define exit locations
• Tailwater elevations
• Simulation Time Selection
• Time steps
• Overall simulation time
Brown & Gay Engineers, Inc.

Segment E 2D Analysis Results: Existing Conditions
Brown & Gay Engineers, Inc.

Segment E 2D Analysis Results: Existing Conditions
Brown & Gay Engineers, Inc.

Segment E 2D Analysis Results: Existing Conditions
Brown & Gay Engineers, Inc.

Segment E 2D Analysis Results: Impact Conditions
Depth Impact
Brown & Gay Engineers, Inc.

Segment E 2D Analysis Results: Proposed Conditions
Amount of 1% (100-yr) sheet flow
needed to pass through the Grand
Parkway: 3,587 cfs
Recommendations:
• 38 Pass-Through culverts
• 8x3 RCBs
• Culvert crown at or below grade
• Pass-Throughs connected to
road-side drainage system
Brown & Gay Engineers, Inc.

2-Dimensional Analysis: Benefits
2D Model Benefits:
• Model flow conditions in situations where 1D conditions
do not exist
• Effective tool for determining watershed sheet flow
patterns, flow depth, and velocity
• Beneficial to model impacts of obstructive fill
• Beneficial to model dispersed drainage solutions for an
overland flow condition
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Introduction
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Existing
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Proposed
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Proposed
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Proposed Velocity
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Proposed Velocity
Brown & Gay Engineers, Inc.

Brazos River Memorial Park: Proposed Velocity
Brown & Gay Engineers, Inc.

2-Dimensional Analysis: Limitations
2D Model Limitations:
• Many 2D models do not meet the minimum modeling
standards for the National Flood Insurance Program.
None are approved for floodway encroachment
modeling.
• 2D model results are limited by the accuracy of the
assumptions, input data and the computing power of the
hardware and software
• Modeling complexity and precision are not a substitute
for sound engineering judgment
Brown & Gay Engineers, Inc.

Thank You!
Questions ?
Brown & Gay Engineers, Inc.