When bulldozers move in to prepare a site for construction, it can spell trouble for the ocean area thatʻs downslope. Disturbed soil without its natural vegetative cover can be blown by wind or transported by rainwater to pollute the ocean with sediment.

Sedimentʻs trademark is murky or brown ocean water that can make it unpleasant or unsafe to swim. Brown water events have happened on Maui even after light rains.

Sediment kills corals

Sediment in the ocean is one of the biggest threats to Maui’s coral reefs. Sediment blocks needed sunlight from reaching the beneficial symbiotic algae that live within the corals. The algae, known as zooxanthellae, can’t live without sunlight. Coral can live without the algae, but not for too long.

Sediment also blocks coral larvae from settling and growing, preventing the formation of new corals.

Prevention is essential

The best solution to sediment in the ocean is… prevention. After learning that a construction site at Kapalua Mauka caused multiple brown water events at DT Fleming Beach — even while the builder was following Maui County’s Best Management Practices — one of our team members developed supplemental guidelines to close the gaps. The suggested additions to the County’s BMPs were presented to Maui County officials and also shared with Kihei Community Association members.

Our recommended BMPs are designed to supplement the existing County guidelines for preventing sediment run-off at construction sites:

    1. The contractor in construction will be responsible to develop a plan to eliminate storm water from the construction site from transporting soil, contaminates, or debris off the site.
    2. For the design of the ultimate storm drainage system, the Contractor will use the Maui Department of Public Works, adoption of Chapter 15-111, Rules for the Design of Storm Water Treatment, Best Management Practices.
    3. The plan will include at a minimum the following additional requirements:
      • No more than one acre shall be cleared of vegetation without measures to eliminate off site sediment transport in place.
      • Silt fences shall be placed down slope from any cleared area and shall remain until the area is either landscaped or developed with structures or hardscape.
      • The silt fences shall be of sufficient height to catch all sediment flow in a storm event. Should the silt fences be over topped, additional row of fences or higher fences shall be immediately installed.
      • Silt basins shall be constructed of sufficient size to allow sediment to be captured before storm water travels off site. If there is sediment that leaves the area, the size of the basin should be increased or additional basins constructed to assure that no sediment leaves the property.
      • The use of hemp mats and sprayed fiber can be used to cover areas cleared of vegetation until construction of improvements or landscaping is in place.
      • Slopes stepper than 3{09706756a260386d8a91e29bb63dc4d846234606f8ff8b495aed1865f6d63d3c} that have been cleared, shall be left unprotected for no more than 48 hours at a time.
      • Straw bales and straw waddles shall be use in critical storm drain areas for temporary reduction of sediment transport.
    4. No clearing shall be allowed during rain events of more than 0.04 inches.
    5. No clearing and grubbing, without approval of the County, will be allowed during the rainy period from October 1 to March 31.
    6. Should brown water occur as a result of the storm runoff from the property under construction even if the sediment comes from off the construction site, the project shall cease construction until further measures are proposed and approved by the County.

We encourage the County of Maui to add these recommendations to their requirements for building and construction on Maui, to help protect our cherished coral reefs and restore clean ocean water to our nearshore areas.

Reef in Brief

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