Experience │ Innovation │ Results

Jeanne C. Hornsby, MS, PE Robert L. Miller, MS, PE Justin M. Shaw, MS, PE

STATE OF THE COAST 2012

PRESENTATION OUTLINE

1) Project Description

2) Acknowledgements

3) Model Setup

4) Model Results

PROJECT LOCATION I-12 TO BUSH, LA

AGENCIES AND CONSULTANTS ENVIRONMENTAL IMPACT STATEMENT

DATA COLLECTION AGENCIES AND CONSULTANTS

LSU Atlas

PROJECT LOCATION EXISTING DRAINAGE BASINS

PROJECT EXTENTS EXISTING FLOW PATTERNS

PROJECT EXTENTS FEMA FLOOD HAZARD ZONES AND WETLAND AREAS

PROJECT EXTENTS SOIL GROUP AND LAND USE

NUMERICAL MODELING PRECIPITATION

0

1

2

3

4

5

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7

8

January February March April May June July August September October November December

Ave

rage

Mo

nth

ly P

reci

pit

atio

n (i

n/m

ont

h)

Average Precipitation per Month

Abita Springs, LA Monthy Precipitation (in)

Covington, LA Monthy Precipitation (in)

Slidell, LA Monthy Precipitation (in)

Statistical Averages: • Wet Days = 109 days/year • Dry Days = 251 days/year • Daily = 0.2 in/day • Monthly = 5.2 in/month • Yearly = 62.7 in/yr • Longest Drought = 51 days • Longest Wet Period = 15 days

Common period of 1973 to 2010

NUMERICAL MODELING MIKE FLOOD

NUMERICAL MODELING EXISTING CONDITIONS

NUMERICAL MODELING EVAULATION CRITERIA

• Increased Flow Constrictions

• Changes to Topography and Canopy

• Impacts to Wetlands

• Variations to Ponding (Inundation)

• Variations to Drought (Drying)

• Water Level Fluctuations

• Changes to Sedimentation and Nutrient Loading*

*Not quantified due lack of channel survey data. Sediment depostion, pollutant

accumulation, and nutrient discharges must be investigated during design phase

NUMERICAL MODELING FLOW CONSTRICTIONS

• Most Common Flow Constriction = Hydraulic Structures

• 118 Structures Modeled in LADOTD Hydraulic Software

• Peak Flows Determined using HEC-HMS

• Scores Evaluated:

• Type of Structure • Size of Structure • Proposed Structure would Replace an Existing Structure

NUMERICAL MODELING TOPOGRAPHY/CANOPY CHANGES

• Scores Evaluated:

• Roadways Constructued on Undeveloped Land • Roadways Constructued on Existing Roadways and Abandoned

Railways

NUMERICAL MODELING DIRECT WETLAND IMPACTS

• Wetlands Delineated by Tetra-Tech within 250 ft Right-of-Way

• Scores Evaluated:

• Wetland Acres within Right-of-Way

NUMERICAL MODELING PONDING/DROUGHT VARIATIONS

• Duration an Area Remains Submerged is a Critical Parameter

Impacting Functionality of Wetlands

• Ponding Duration Leads to Changes in Wetland Type, Function, and

Quality

• Ponding/Drought: Changes to Water Surface Extent or Inundation

• Scores Evaluated:

• Ponding: Inundated Areas Compared to Existing Conditions • Drought: Dry Areas Compared to Existing Conditions

NUMERICAL MODELING PONDING/DROUGHT VARIATIONS (7-DAY)

Ponding:

Drought:

NUMERICAL MODELING PONDING VARIATIONS (7-DAY)

NUMERICAL MODELING DROUGHT VARIATIONS (7-DAY)

NUMERICAL MODELING WATER LEVEL FLUCTUATIONS (2-YEAR STORM EVENT)

• Difference in Maximum and Minimum Water Levels in a Wetland

• Changes in Wetland Water Level may cause a Consistent Delince in

Diversity and an Increase in Invasive Species

• Scores Evaluated:

• Change in Water Suface Exceeded 0.025 m

NUMERICAL MODELING WATER LEVEL FLUCTUATIONS (2-YEAR STORM EVENT)

NUMERICAL MODELING ALIGNMENT COMPARISON

NUMERICAL MODELING ALIGNMENT COMPARISON

1 2 3 4

CONCLUSIONS

Hydrodynamic Numerical Model

Alignment Evaluation with Categorical Rating System

Dominant Factors of Constructing Roadways through Wetland

Systems:

• Roadway Placement and Orientation

• Basin Gradient

• Channel Crossings

Experience │ Innovation │ Results

WATER RESOURCES Hydraulic & Hydrologic Engineering

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