Four Mile Swamp Floodplain Analysis, St. Johns County, Florida

The City of St. Augustine contracted with Humphries Consulting & Engineering, Inc. to conduct a floodplain analysis of the adjacent Four-Mile Swamp.  This involved an analysis of approximately 6.8 square miles of drainage area to the point where a downstream trail road clearly impounded floodwaters with a free tailwater condition.  Because of the availability of 2-foot topographic contours from St. Johns County, HEC-GeoHMS and HEC-Geo RAS were used to expedite the study process and create HEC-HMS and HEC-RAS models of the swamp.  A certified report was provided to the City documenting the flood elevations. 

Haywood Estates Culvert Sizing and Conditional Letter of Map Revision, Jacksonville Beach, Florida

The Habitat for Humanity of the Jacksonville Beaches proposed to construct a new development which required a regulatory floodway crossing for access to the property.  The Sherman Creek Canal is a tidally influenced stream that drains approximately 1.5 square miles of urban area and has an identified floodway in the Duval County Flood Insurance Study. 

For this project, Humphries Consulting & Engineering, Inc. was contracted to determine the proper size for the stream crossing in order to eliminate or minimize the impact to the 1% Annual Chance and Floodway hydraulic profiles within the budget constraints of the project.  The Flood Insurance Study HEC-2 hydraulic model was revised with cross sections in the vicinity of the proposed crossing and it was determined that an official “No-Rise Certification” from the published profiles would not be possible based on existing stream conditions.  Of the possible crossing types, it was determined that a box culvert would be most economical for the project.  A double box culvert that minimized the upstream impact to the hydraulic profile was designed and a Conditional Letter of Map Revision was granted from FEMA.  Because the changes to the hydraulic profile were less than 0.1 feet, and the floodway width and alignment were maintained from the original Flood Insurance Rate Map, no increases to the Flood Insurance Study hydraulic profile were warranted. 

Hefferon Drive Bridge Scour Analysis, St. Augustine, Florida

Humphries Consulting & Engineering, Inc. was contracted to conduct a bridge scour and recommendation analysis for the Hefferon Drive Bridge in the Heritage Park subdivision in St. Johns County, Florida.  To begin the project, surveys, bridge plans and As-Builts of the bridge were reviewed.  In order to begin the numerical analysis, the existing FEMA flood insurance study hydraulic analysis and historical stream information was obtained for Red House Branch.  A hydrologic evaluation of flooding events at the bridge crossing location was then made in accordance with FDOT and FHWA specifications.

The FEMA HEC-RAS analysis was then updated to include the actual constructed bridge conditions.  A bridge scour model was then created according to FDOT, FHWA, HEC-18 (Hydraulic Engineering Circular 18), HEC-20, and HEC-23 specifications.  The potential depth of scour for the specified return events was evaluated using the procedures recommended in those publications.

A detailed report containing the methods and background information, the hydraulic analysis, and the scour results was prepared.  The final deliverable also included hydraulic recommendations for bridge protection, preparation a Bridge Hydraulics Recommendation Sheet and Bridge Hydraulics Report per FDOT specifications, and certification that the scour protection was constructed according to specifications.

St. Johns County Emergency Operations Center (EOC), St. Johns County, Florida