Highway Hydraulic Engineering State of Practice (2020)

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65 The conclusions summarize the literature review, survey responses from 38 state DOTs, and interviews and case example documentation provided by state DOT hydraulic engineers in four states to provide a snapshot of the state of the practice. The synthesis found that advances in the selected topics occurred for a variety of reasons, including advances in technology, cost saving measures, FHWA initiatives, safety concerns, and increased frequency of severe rainfall events and flood hazards. With these advances came changes in agency responsibilities, technological challenges, and policy updates in some states. A summary of key findings is as follows: Roadway Drainage • 8% (3) of the 38 states responded indicating a change to include spread calculations for temporary construction; • 3% (1) of the 38 states responded indicating that policy is pending to include spread calcula- tions for temporary construction; • 8% (2) of the 38 states responded indicating a change in roadway drainage policy to design for reduced efficiency of pipe culverts or pipe culvert/headwalls (due to debris); and • 16% (6) of the 38 states responded indicating a change in design for reduced inlet efficiency (due to debris). Culvert Aquatic Organism Passage • 76% (29) of the 38 states responding reported changes in culvert replacement and rehabilita- tion practices for sensitive aquatic organism passage and habitats. • From literature it was discovered that: – Advances in culvert aquatic organism passage design include stream simulation, with goals of providing unrestricted movements and rehabilitations for natural channels where possible; and – Detailed design processes for aquatic organism passage are available, and case-by-case evaluation of conditions is preferred. Bridge Scour Computations and Countermeasures • 53% (20) of the 38 responding states made a change either to their scour calculation method or their scour countermeasure selection or design method; and C H A P T E R 5 Conclusions

66 Highway Hydraulic Engineering State of Practice • From literature it was discovered that reasons for changes in bridge scour computations and countermeasures include lack of data, uncertainty in rock characteristics and appropriate sediment size to input into scour equations, suspected over-prediction of scour, counter- measure failure, and uncertainty in dealing with cohesive soils. Advanced Hydraulic Modeling • 47% (18) of the 26 responding states reported at least some use of advanced hydraulic modeling—either unsteady or 2D/3D flow modeling—for projects; • No states responding from EPA Standard Federal Regions 5 or 9 reported using unsteady flow modeling for projects. In Regions 3, 4, 7, 8, and 10, no states reported sediment transport models being implemented within the last 10 years; • From literature and case examples, it was discovered that decisions to change practice to 2D hydraulic modeling have involved evaluation of technical aspects, time requirements, available data, and experience. To overcome challenges, FHWA Everyday Counts initiatives include use of next-generation hydraulic applications, specifically 2D modeling, to improve understanding of interactions between transportation assets and river environments. Many state DOTs have joined FHWA in this effort as FHWA has partnered in pilot projects and provided National Highway Institute courses with licenses for DOTs; • From literature it was discovered that 2D models are accepted by FEMA if the NFIP require- ments for flood hazard mapping activities are met; and • From literature it was discovered that Utah requires 2D use for bridge models. Regulatory Requirements • Of the 38 states that responded: – 55% (21) indicated they have programmatic agreements for FHWA National Environmen- tal Policy Act; – 29% (11) have agreements for Section 404 of the CWA; – 18% (7) have agreements for local floodplain requirements; and – 24% (9) have agreements for the NPDES. • From literature it was discovered that if any new development or redevelopment generates an acre or more of impervious surface, Hawaii requires LID stormwater management practices for treatment of MS4. These practices, including swales, bioretention, infiltration trenches, and engineered wetlands are to treat the water quality design volume. Floodplain Impacts and Mitigation • From literature it was discovered that: – Standard operating procedures for review of less complex construction and maintenance projects in floodplains—specifically for “no rise” or no change in 100-year water surface elevation or base flood elevation—are able to expedite reviews and project implementa- tion; and – Revised procedures and DFIRM databases using GIS can aid in incorporating duplicate hydraulics models so that only one is necessary for FEMA acceptance. Coastal Hydraulics • Only one of 38 responding states reported that its policy or guidelines for coastal scour pro- tection has changed in the last 10 years;

Conclusions 67 • One state of 38 responding states reported having policies pending for a range of coastal pro- tection measures; • Five (13%) of 38 responding states reported current or pending policy or guidance on specific design practices for flood protection of roadways from erosion due to waves or changes in water surface elevation; and • Eight (21%) of 38 responding states indicated that they have policies or procedures addressing coastal hydraulics, and these consist of a mix of policies for structure hydraulic response to waves; armor protection loading response; foundation soil loads; and scour protection. [Note: There are 31 total coastal states.] – Two states currently address structure hydraulic response to waves; – Three address armor protection loading response; – One addresses foundation soil loads; and – Four address scour protection. Alternative Project Delivery Methods • Twelve (32%) of the 38 responding states reported changing policy or guidance within the last 10 years to include RFP language for hydraulic aspects of alternatively delivered projects.