This document discusses hydrologic and hydraulic analysis using ArcGIS, Arc Hydro, and HEC-RAS to develop scour plans of action for critical bridges in Hawaii. It describes a 5-step process: 1) estimating peak discharges, 2) field reconnaissance, 3) creating hydraulic models and computing scour, 4) developing countermeasures, and 5) preparing scour plans. Case studies are presented for bridges on Kauai, Maui, and Oahu that illustrate challenges like high rainfall, proximity to the ocean, and tsunamis. The document emphasizes developing customized scour plans of action for the Hawaii Department of Transportation using templates from other agencies.

1. 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

2. 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)

3. 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

4. Maui Big Island
Molokai Kauai

5. Step 1.
Estimate Peak Discharges
 Flood-frequency analysis
 USGS regression equations
 Available peak discharges (FEMA, Corps)
Maui Big Island

6. Data: Software:
 National Bridge  ArcGIS, Spatial Analyst,
Inventory 3D Analyst
 DEM  Arc Hydro
 Streams  Google Earth
 Imagery
 Rainfall
 Available stream gage
locations and data

7. Step 1.
Estimate Peak Discharges
 Flood-Frequency Analysis  Regression Equations
(~30% of Bridges) (New in 2010)

8. •50-foot DEM
•Streams layer
•Mean annual rainfall
•Arc Hydro

9. Kauai Scour
Critical Bridge
Watersheds
Mt. Wai‘ale‘ale:
450 to 500
inches per year!
Wailua River
DA = 53 mi2
Q100: 104,000 cfs

10. Step 2.
Perform Field Reconnaissance
 Obtained As-builts
 Customized Field Form
 Field Recon Team:
 Structural Engineer
 Hydraulic Engineer
 Geotechnical Engineer

11. Field Form

12. Field Form
(cont’d)
Mauka = toward the mountains, inland
Makai = toward the sea

13. Vertical Datum?
Field Form
(cont’d)

19. Local Fish
& Wildlife
(found
under the
bridges)

20. Hakalau Bridge
 Built in 1953  Sand with surface gravel
 100-Yr Discharge is 5,710 cfs  170-ft high deck

21. Hakalau Bridge

22. Step 3.
Create Hydraulic Model &
Compute Scour  HEC-RAS
 HEC-18 scour
 NCHRP reports

23. Data: Software:
 Intermap IfSAR DTM  ArcGIS, Spatial Analyst,
v1.5 3D Analyst
 NED DEM 10-meter  HEC-GeoRAS
 Hillshade models  HEC-RAS
 Contours
 Imagery
 As-built bridge plans

24. •Intermap IfSAR DTM v1.5
•Coastal Geology Group Imagery
•HEC-GeoRAS

26. 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)

27. Wailuku River Bridge
& Tsunami Path
USGS

29. Step 4.
Develop Scour Countermeasures
& Recommend Actions
 Hydraulic/Structural Countermeasures:
 Riprap Relief bridge / culvert
 Spurs/ Bendway weirs/ Barbs Substructure modification
 Drop structure Recommend bridge replacement
 Channel improvements
 Increased inspection frequency
 Scour monitoring devices
 Flood monitoring plan

30. Waikapu Bridge
 Built in 1937
 100-Yr Discharge: 1,180 cfs
 Boulders and bedrock
 Footings undermined

31. Waikapu Bridge
 5-6 ft degradation
based on 1935 as-builts
 Countermeasure
options:
 Grout injection
 Re-establish grade at
downstream end
 Drop structure

32. Waimea River Bridge (Oahu)
 Built in 1928
 100-Yr Discharge: 12,440 cfs
 Sand and Silt Bed
 Multiple Piers and Piles

33. Waimea River Bridge
 Pier 2 Undermined
 Damage to Riprap at
Abutments
 Debris in Channel
 Proposed
Countermeasures:
12 ft  Repair Existing Riprap
 Riprap Base of Piers
 Remove Debris

34. Step 5.
Prepare Scour Plan of Action
 Template – Caltrans
 Additions
 Illinois DOT, FHWA
 Customized for
Hawaii DOT

35. 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

36. Scour POA – Recommended Actions

37. Scour POA – Bridge Closure
 Critical Scour Elevations
 Provides Guidance to
HDOT Personnel

38. Scour POA – Detour Route
Hana Highway

39. Scour POA – Bridge Scour Schematic

40. Questions?
Contact Info:
Kurt Baron, GISP
WEST Consultants, Inc.
kbaron@westconsultants.com
(858) 487-9378