Preparing Scour Critical Plans of Action for Hawaiian Bridges - Hydrologic and Hydraulic Analysis using ArcGIS, Arc Hydro, and HEC-GeoRAS

Kurt Baron
Christine Parente
Martin Teal
WEST Consultants, Inc., San Diego, CA
Mike Hunnemann
KAI Hawaii, Inc., Honolulu, HI
Curtis Matsuda
Hawaii DOT, Kapolei, HI

Disaster Management and Emergency Response I
Monday March 5, 2012 - 10:45 am to noon

Approximately 60 bridges have been identified as potentially scour critical in the state of Hawaii based on observed or anticipated conditions at the bridges.　 These studies allowed the Hawaii Department of Transportation to prepare a Plan of Action (POA) for each bridge, which includes a scour vulnerability assessment and recommended actions, including a bridge closure plan.

Bridges involved in this effort cross waterways ranging from large, sand-bed rivers along the coastline of Oahu to the steep, rocky Hamakua Coast on the Big Island.　 Several bridges further inland are located on steep, cobble and boulder streams.　 A number of bridges on the historic Hana Highway on Maui are also included, with construction dating from as early as 1912.　 Drainage areas range from less than 0.5 km2 for some small coastal bridges to nearly 650 km2 for the Wailuku River (on the Big Island), which is subject to not only riverine scour, but also to scour from a tsunami-generated tidal bore.

Arc Hydro and ArcGIS were used to determine the areas contributing to streamflow at each bridge and flows were developed based on flood frequency gage analysis, regional regression equations, or published FEMA flows. Scour vulnerability of each bridge was determined by a detailed hydraulic analysis using HEC-GeoRAS and the HEC-RAS hydraulic model.　 Based on the scour vulnerability and foundation material and type, a POA was developed specific to each bridge describing procedures for Hawaii DOT personnel to follow during high flow events to ensure public safety.