Highway Hydraulic Engineering State of Practice (2020)

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1 The objective of this synthesis is to document significant changes in highway hydraulic engineering practices implemented by state departments of transportation (DOTs) over the past decade. The synthesis focuses on eight subtopics of highway hydraulic engineer- ing: Roadway Drainage; Culvert Aquatic Organism Passage; Bridge Scour Computa- tions and Countermeasures; Advanced Hydraulic Modeling; Regulatory Requirements; Floodplain Impacts and Mitigation; Coastal Hydraulics; and Alternative Project Delivery Methods. The information was gathered through literature review, a survey of state DOTs, and interviews with selected agencies for case examples of early adoption of new engineering practices. The questionnaire was emailed to state hydraulic engineers in all 50 states, the District of Columbia, and Puerto Rico. Thirty-eight responses were received for a 73% response rate. Major findings in each subtopic area based on survey responses include: Roadway Drainage • 34% of 38 responding states indicated that their hydraulic policy or guidance changed within the past 10 years with respect to maximum allowable spread in travel lanes and/or the design event frequency for permanent/final designs. • 8% of 38 responding states indicated changes in design policy for allowable spread for temporary construction. Culvert Aquatic Organism Passage • 55% of 38 responding states reported changes in culvert replacement and rehabilitation practices for Culvert Aquatic Organism Passage. Bridge Scour Computations and Countermeasures • 53% of 38 responding states made a change to their scour calculation method, scour countermeasure selection, or design method. Advanced Hydraulic Modeling • 96% of 26 responding states reported some use of advanced hydraulic modeling—either unsteady or 2D/3D flow modeling—for projects. S U M M A R Y Highway Hydraulic Engineering State of Practice

2 Highway Hydraulic Engineering State of Practice • No states responding from EPA Standard Federal Regions 5 or 9 required unsteady flow modeling for projects. • In EPA Standard Federal Regions 3, 4, 7, 8, and 10, no states reported sediment trans- port models being implemented within the last 10 years. Regulatory Requirements • Of the 38 states that responded: – 55% indicated they have programmatic agreements for the FHWA National Envi- ronmental Policy Act project development process; – 11% have Programmatic Agreements for Section 404 of the Clean Water Act (CWA); – 21% have Programmatic Agreements for local floodplain requirements; – 24% have Programmatic Agreements for the National Pollutant Discharge Elimination System; and – Changes to these regulatory requirements were made in the last decade by 21%, 29%, 32%, and 47% of state DOTs, respectively. Floodplain Impacts and Mitigation • Of the 24 states that responded to changing policy or guidance for floodplain impacts, 75% indicated no change or that they are following previous policy or guidance. • Of the 24 states that responded to changing policy or guidance for mitigation, 79% indi- cated no change or that they are following previous policy or guidance. Coastal Hydraulics • 33% of 24 ocean and Great Lakes states participated in the survey and responded. They indicated that they have policies or procedures addressing coastal hydraulics, specifically structure hydraulic response to waves; armor protection loading response; foundation soil loads; and/or scour protection. (Note: There are 31 total coastal states.) Alternative Project Delivery Methods • Of the 21 states that responded to changing policy or guidance within the last 10 years to include request for proposal (RFP) language for hydraulic aspects of alternatively delivered projects, 57% replied yes to including such language.