Phase 4 Drainage - Drainage Masterplan

Michael Horton of Davis & Floyd presented a draft report of the Comprehensive Drainage
Master Plan. The scope of the plan covers 30th Avenue to Breach Inlet and provided suggestions
for improvements along with potential costs, the creation of a maintenance program, and a
review of the City’s current development standards and recommendations for revisions. 

Next Steps: 

The Planning Commission will
complete a more comprehensive review of the plan and staff will continue to analyze it as well.
The Environmental Advisory Committee has also asked to review it.

Work in Progress and/or Complete:

• D&F’s main focus has been supporting the city with their SCIIP grant application which was submitted September 8th.
• High-priority solutions/recommendations complete.
• Cost estimates are complete for 6th/7th Avenue and 2nd Avenue/Charleston Boulevard – These are part of the SCIIP grant request.
• Finalizing remaining high-priority recommendation cost estimates once data required for SCIIP application is complete.
• Groundwater monitoring well installed at 6th Avenue to validate conceptual designs.
• Low-priority conceptual solutions and recommendations are nearing completion. These are in the QA/QC process and then cost estimates will be developed.
• D&F met with property owners and city staff regarding development regulations.

Next Steps:

• Analyze list of island-wide priorities identified by Public Works and develop priority list.
• Finalize cost estimates for all high-priority solutions.
• Develop preliminary cost estimates for low priority recommendations.
• Develop city-wide development planning tool for stormwater management. 

Work in Progress and/or Complete:

• D&F’s main focus has been supporting the city with their SCIIP grant application to meet the September 12th deadline.
• High-priority solutions/recommendations complete
• Cost estimates are complete for 6th/7th Avenue and 2nd Avenue/Charleston Boulevard – This are part of the SCIIP grant request.
• Finalizing remaining high-priority recommendation cost estimates once data required for SCIIP application is complete
• Groundwater monitoring well installed at 6th Avenue to validate conceptual designs
• Low-priority conceptual solutions and recommendations are nearing completion. These are in the QA/QC process and then cost estimates will be developed.
• D&F met with property owners and city staff regarding development regulations.

Next Steps:

• D&F to provide required documentation for SCIIP application (e.g., exhibits, cost estimates, PER, etc.)
• Finalize cost estimates for all high-priority solutions
• Develop preliminary cost estimates for low priority recommendations
• Develop city-wide development planning tool for storm water management

Work in Progress:

• Finalizing solutions for high-priority areas
  • Working with manufacturer to develop preliminary design for dune infiltration system at Ocean Boulevard and 6th & 7th Avenues
  • Working with city to identify potential locations for additional/new check valves

• Developing solutions for low-priority areas to address potential capacity issues
• Working with RIA to prepare for applying for grants to implement high-priority projects
• Met with residents to evaluate storm water regulations with regards to new development

Next Steps:

• Consider proposal to install a ground water evaluation monitoring equipment at the site of potential due infiltration system installation area
• Develop cost estimates for solutions for high-priority areas
• Finalize solutions and develop cost estimates for low-priority improvements
• Continue identifying funding options for all alternatives
• Davis & Floyd has identified two projects that would be eligible for funding from the Rural Infrastructure Authority and the South Carolina Infrastructure Investment Program (funded by ARPA). Staff will coordinate development of grant applications by deadline in mid-September.

Work in Progress:

• Finalizing solutions for high-priority areas
  • Working with manufacturer to develop preliminary design for dune infiltration system at Ocean Boulevard and 6th Avenue
  • Working with city to identify potential locations for additional/new check valves

• Developing solutions for low-priority areas to address potential capacity issues
• Working with RIA to prepare for applying for grants to implement high-priority projects
• Set up meeting with local resident to evaluate stormwater regulations with regards to new development

Next Steps:

• Develop cost estimates for solutions for high-priority areas.
• Finalize solutions and develop cost estimates for low-priority improvements
• Continue identifying funding options for all alternatives.
• Complete analysis of local resident development project to evaluate stormwater regulations.

Work Complete to Date:

• Full inventory and assessment of existing drainage infrastructure for phase 4 study area.
• Water level monitoring stations installed near Ocean Boulevard, county park, and marina.
• Rainfall monitoring station installed at county park.
• Provided short-term maintenance recommendations based on field assessments for phase 4 study area.
• Completed existing conditions hydrologic and hydraulic assessments of phase 4 infrastructure for both extreme and typical storm events. This includes high intensity rain bombs as well as elevated tides from sea level rise.
• Developed preliminary solutions for high-priority areas within the phase 4 study area as identified through the existing conditions assessment and confirmed by city staff. High-priority areas are classified as those that experience more than 6 inches of flooding for more than 30 minutes.
• Identified preliminary solutions for low-priority areas within phase 4 study area.
• Reviewed island-wide ditch/channel maintenance program.

Next Steps:

• Develop cost estimates for preliminary solutions for high-priority areas.
• Continue evaluating alternatives for high-priority areas to fiend the most efficient and economical long-term solution.
• Continue evaluating options to solve flooding in low-priority areas.
• Identify funding options for all alternatives.
• Set up meeting and work with residential property owners to evaluate development standards in terms of stormwater management.
• Identify and consult with specialty contracts (e.g., stream restoration contractors) to develop long-term solution for island-wide canal/ditch/channel systems.