HYDROLOGIC AND HYDRAULIC ANALYSIS USING ARCGIS, ARC HYDRO, AND HEC-GEORAS

Kurt Baron, GISP, WEST Consultants, Inc.

A. Jake Gusman, P.E., WEST Consultants, Inc. Christine Warren, P.E., WEST Consultants, Inc.

Martin J. Teal, P.E., P.H., WEST Consultants, Inc. Mike Hunnemann, P.E., KAI Hawaii Inc.

Curtis Matsuda, P.E., Hawaii DOT

Scour POA Development

1. Estimate Peak Discharges

2. Perform Field Reconnaissance

3. Create Hydraulic Model & Compute Scour

4. Develop Scour Countermeasures

5. Prepare Scour Plan of Action

Lumahai River

Bridge (Kauai)

Scour Critical Bridges - Hawaii

56 Hawaiian Bridges Identified as Scour Critical:

21 on Oahu

13 on the Big Island

10 on Maui

10 on Kauai

2 on Molokai

Drainage Areas: 0.2 mi2 to 250 mi2

Many within 500 ft of the ocean

Oahu

Maui Big Island

Kauai Molokai

Step 1.

Estimate Peak Discharges

Flood-frequency analysis

USGS regression equations

Available peak discharges (FEMA, Corps)

Maui Big Island

Data: National Bridge

Inventory

DEM

Streams

Imagery

Rainfall

Available stream gage locations and data

ArcGIS, Spatial Analyst, 3D Analyst

Arc Hydro

Google Earth

Software:

Regression Equations

(New in 2010)

Step 1.

Estimate Peak Discharges Flood-Frequency Analysis

(~30% of Bridges)

•50-foot DEM

•Streams layer

•Mean annual rainfall

•Arc Hydro

Kauai Scour

Critical Bridge

Watersheds

Mt. Wai‘ale‘ale:

450 to 500

inches per year!

Wailua River

DA = 53 mi2

Q100: 104,000 cfs

Step 2.

Perform Field Reconnaissance

Obtained As-builts

Customized Field Form

Field Recon Team: Structural Engineer

Hydraulic Engineer

Geotechnical Engineer

Field Form

Field Form (cont’d)

Mauka = toward the mountains, inland

Makai = toward the sea

Field Form (cont’d)

Vertical Datum?

Local Fish & Wildlife (found under the bridges)

Hakalau Bridge Built in 1953

100-Yr Discharge is 5,710 cfs

Sand with surface gravel

170-ft high deck

Hakalau Bridge

Step 3.

Create Hydraulic Model & Compute Scour HEC-RAS

HEC-18 scour

NCHRP reports

Data: Intermap IfSAR DTM

v1.5

NED DEM 10-meter

Hillshade models

Contours

Imagery

As-built bridge plans

ArcGIS, Spatial Analyst, 3D Analyst

HEC-GeoRAS

HEC-RAS

Software:

•Intermap IfSAR DTM v1.5

•Coastal Geology Group Imagery

•HEC-GeoRAS

Wailuku River Bridge Flood flows (Q100: 135,000 cfs) and tsunami bores

Tsunamis occurred in 1946 (Aleutian Islands earthquake), 1960 (Chilean quake)

1960 Tsunami

(USGS)

Wailuku River Bridge & Tsunami Path

USGS

Step 4.

Develop Scour Countermeasures & Recommend Actions Hydraulic/Structural Countermeasures:

Increased inspection frequency

Scour monitoring devices

Flood monitoring plan

Riprap Spurs/ Bendway weirs/ Barbs Drop structure Channel improvements

Relief bridge / culvert Substructure modification Recommend bridge replacement

Waikapu Bridge Built in 1937

100-Yr Discharge: 1,180 cfs

Boulders and bedrock

Footings undermined

Waikapu Bridge

5-6 ft degradation based on 1935 as-builts

Countermeasure options: Grout injection

Re-establish grade at downstream end

Drop structure

Waimea River Bridge (Oahu) Built in 1928

100-Yr Discharge: 12,440 cfs

Sand and Silt Bed

Multiple Piers and Piles

Waimea River Bridge

Pier 2 Undermined

Damage to Riprap at Abutments

Debris in Channel

Proposed Countermeasures:

Repair Existing Riprap

Riprap Base of Piers

Remove Debris

12 ft

Step 5.

Prepare Scour Plan of Action

Template – Caltrans

Additions Illinois DOT, FHWA

Customized for

Hawaii DOT

Scour POA Form Sections 1. Scour Vulnerability

2. NBIS Coding Information

3. Recommended Action(s)

4. Hydraulic/Structural

Countermeasures

5. Inspection Frequency

6. Monitoring Devices

7. Flood Monitoring Plan

8. Bridge Closure Plan

9. Detour Route

10. Bridge Scour Schematic

Scour POA – Recommended Actions

Scour POA – Bridge Closure

Critical Scour Elevations

Provides Guidance to HDOT Personnel

Scour POA – Detour Route

Hana Highway

Scour POA – Bridge Scour Schematic

Questions?

Contact Info:

Kurt Baron, GISP

WEST Consultants, Inc.

kbaron@westconsultants.com

(858) 487-9378