Integrating Fluvial Geomorphology and Hydrology into Post-Irene Permanent Repairs and Flood Vulnerability Mapping along the

Vermont State Highway System

Evan Fitzgerald Sept 24, 2014

Fitzgerald Environmental 18 Severance Green, Suite 203 Colchester, VT 05446 www.fitzgeraldenvironmental.com

VTrans Geomorphology Assistance

• Shayne Jaquith from DEC Rivers participated in Fall 2011 Scan Tour

• Evan Fitzgerald participated in Spring 2012 Scan Tour

• Visited >500 Sites to determine stability, costs, and permitting needs

• 130 sites with river embankment repairs or crossings were identified for Districts to

manage contracts for permanent repairs

• Dozens of other unstable sites were identified for PDD responsibility due to the

project complexity and/or anticipated repair costs (e.g., >$250K)

Stable Unstable

Typical Embankment Repair Site - Design

• Visit sites with District staff to make site observations and

collect data for channel and road embankment

dimensions

• Determine drainage area and reference channel width

using VTDEC hydraulic geometry regressions

• Develop site-specific sketches for embankment repair

• Determine fill areas below OHW for ACOE and VTDEC

clearances

Before After

18ft

25ft

• Participate in pre-bid and pre-construction meetings with District Staff

• Project stake-out, discussion of permit conditions, work sequencing

• 2-3 oversight visits and final inspection with District Staff

Typical Embankment Repair Site - Construction Oversight

Marlboro-Brattleboro VT-9

1.2 DDIR sites/mile

Wardsboro-Jamaica VT-100

1.5 DDIR sites/mile

Andover-Chester VT-11

1.7 DDIR sites/mile

Cavendish-Weathersfield VT-131

1.6 DDIR sites/mile

Plymouth-Bridgewater VT-100 3.3 DDIR sites/mile

Rutland-Hartford US-4

1.0 DDIR sites/mile

Goshen-Rochester VT-73

2.1 DDIR sites/mile

Killington-Stockbridge VT-100

2.1 DDIR sites/mile Stockbridge- Rochester VT-100 2.5 DDIR sites/mile

Randolph-Northfield VT-12A 1.3 DDIR sites/mile

VT 9, Marlboro

VT100, Killington

LiDAR – Light Detection and Ranging

• Airborne laser combined with

GPS controls

• Point cloud with X,Y, and Z

• FEMA specifications for vertical

accuracy = 18.5cm (0.61ft)

• Topographic LiDAR does not

penetrate water well

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LiDAR Profiles of River-Road Corridors VT100 North, Killington South Branch Tweed River (White River Basin)

Flood Vulnerability Mapping Using LiDAR Data

Process-based approach to identify and prioritize risk in river-roadway corridors: 1. Hydrologic and hydraulic modeling (HEC-RAS) to quantify river and floodplain erosion potential. 2. LiDAR slope mapping to identify slopes >100% in between roadway and river. 3. Identify areas of roadway with limited relief from river that are susceptible to erosion during flood events.

Hydrologic Engineering Center’s River Analysis System (HEC-RAS)

• Army Corps of Engineers Hydrologic-Hydraulic Modeling Tool

• Used for FEMA Flood Hazard Modeling, River Engineering and Restoration, Sediment Modeling

• Based on Manning’s equation and energy loss equations

• One dimensional model of velocity and water surface profiles

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Lower_Cold_River_Vtrans Plan: VTRANS_current 6/10/2013

Main Channel Dis tance (ft)

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ft)

Legend

WS PF 7

WS PF 6

WS PF 5

WS PF 4

WS PF 3

WS PF 2

WS PF 1

Sediment Fill

Ground

Left Levee

Right Levee

Cold River 2

VT100 North, Killington, South Branch Tweed River

TS Irene Damage Site DDIR D3-30

Roadway-River Geometry and Flood Vulnerability

VT100 North, Killington, South Branch Tweed River (DDIR D3-28)

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VT 100 Embankment Slope 1:1 = 100% or 45°

Height of roadway above channel bottom (ft)

VT100 PDD Corridor Project Road Data • Killington – Stockbridge (10.7mi) • 23 TS Irene damage sites total • 11 damage sites concentrated along 3.5 miles in Killington and Pittsfield

River Data • South Branch Tweed River • 3rd and 4th order stream • Drainage area: 5 - 15 square miles • Bankfull channel: 25 - 40ft

Known damage site

Unknown erosion site

Previously armored site

Natural Bedrock Armoring in Channel and Banks

150ft of erosion, 6-8ft high, within 3-6ft of shoulder

Flood Vulnerability Mapping Using LiDAR Data

Observations from VT100 Corridor Model: 1. 8 of 11 damage sites in Rt. 100 corridor are associated with highest levels of river shear stress (i.e., erosion potential). 2. Bedrock in channel and banks provides grade control and natural armor. 3. Previously armored embankments were found in areas predicted as vulnerable.

Site Type #

Severe Erosion 3

Minor Erosion 3

Previously Armored 2

Natural Armor 2

Total 10

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Vermont Rivers and Streams

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Vermont Rivers and Streams

River/Streams in Proximity to Major Roadways (25m)

Note: River-Roadway intersect completed using GIS at a cursory level.

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Vermont Rivers and Streams

River/Streams in Proximity to Major Roadways (25m)

DDIR Irene Damage Sites

Note: River-Roadway and River-DDIR intersects completed using GIS at a cursory level.

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Vermont Rivers and Streams

River/Streams in Proximity to Major Roadways (25m)

DDIR Irene Damage Sites

Stream Power

Note: River-Roadway and River-DDIR intersects completed using GIS at a cursory level.

Summary

• There are areas of roadway instability triggered by TS Irene that were not programmed for stabilization.

• LiDAR data is an important tool for facilitating sound flood recovery and flood vulnerability mapping efforts.

• Statewide LiDAR data collection for flood vulnerability mapping should be prioritized based on physical settings as well as flood damage history.

• Q100 velocity or shear stress are likely the best predictors of flood vulnerability in 3rd and 4th order streams.

• In higher order rivers (e.g., 5th order), two-dimensional modeling may enhance flood vulnerability mapping.

Questions?