Department of Public Works West Maui Storm Drainage August 20, 2019 - PowerPoint PPT Presentation

Department of Public Works West Maui Storm Drainage August 20, 2019 West Maui Community Plan Meeting Ready & Resilient Systems

County of Maui West Maui Drainage Systems � Underground drainlines within County right of way � Sediment and debris basins � Flood control systems

County Drainage Facilities � Underground Drainage System in Lahaina Town � 5 - DLNR Regulated Sediment Basins � Honokowai � Kahana Nui � Kaopala � Napili 4-5 � Napili 2-3 � 3 - Unregulated Sediment Basins � Honokeana � S-Turn � Mahinahina � Kahoma Stream Flood Control � Lahaina Watershed Flood Control (Lahainaluna to Launiupoko)

Underground Drainage Systems � Existing corrugated metal pipes are failing � What’s next? � Drainage system inventory of West Maui recently completed � Drainline condition assessment recently contracted to consultant � Prioritize drainage systems needing repair � Secure funding

Sediment Basins & Flood Control Systems � Reduces sediment entering near shore waters � Highways Division’s maintenance: � Remove sediment build up and debris � Inspect during and after a large storm event and submit reports to DLNR for regulated basins � Drone surveys used to determine the extent of sediment removal needed

Drainage Issues � No access prevents Highways Division from clearing culverts/channels � Property owners need to keep drainage easements clear; no trees, structures, fences, etc. � No dumping of green waste in drainageways please! � Ponding problems due to lack of drainage systems � Need evaluation of problem areas � Seek funding

Drainage Issues � Flooding � Completion of Lahaina Watershed Phases 3B, 4, & 5 is necessary � Sea level rise causing more sand plug build up at drain outlets � Sand plugs lowered by Highways in anticipation of large storm events � Continuous maintenance required to keep debris basins clear and functional

Lahaina Watershed Project Status � Next phase to construct – Phase 3B at Kauaula Stream � 3B plans need revisions to address continuous stream flow � Environmental studies to be updated � NRCS to seek construction funds

Considerations for Development/Redevelopment � Comply with County’s Rules: � Title MC-15, Chapter 4 - Storm Drainage Facilities � Title MC-15, Chapter 111 - Storm Water Treatment BMPs � Additional runoff generated must be retained onsite � LID (Low Impact Development) design is encouraged � Use Best Management Practices for sediment & erosion control

Community Plan Suggestions Objectives and Policies: � Ensure that drainage systems comply with the County’s drainage rules. � Incorporate post-development BMPs into project planning. � Pursue funding sources to fund drainage infrastructure. � Encourage the use of low impact development (LID) techniques for all new developments, roadway projects, and Capital Improvement Projects. � Ensure that new developments will not result in adverse flooding conditions for downstream properties by requiring onsite retention facilities for stormwater run-off generated by the development.

Community Plan Suggestions Implementing Actions: � Update the Lahaina Town Drainage Master Plan. � Complete the Lahaina Watershed Flood Control project. � Establish a comprehensive stormwater management plan that emphasizes the use of natural drainage systems where possible. � Complete an inventory of drainage facilities in West Maui for use in developing long-term plans for addressing stormwater issues. � Encourage the use of underground utilities and coordinate utility placement with road improvements.

MAHALO! Rowena Dagdag-Andaya Director Department of Public Works