Kahului Harbor

The State of Hawaii Department of Transportation Harbors Division (DOT-HAR) is proceeding with implementation of improvements at Kahului Harbor, Maui, as outlined in the Kahului Commercial Harbor 2025 Master Plan, September 2000.

An Environmental Assessment was prepared to assess the potential for significant impacts by the proposed harbor improvements. The proposed construction, particularly dredging and in-water construction, may have direct or indirect impacts on marine biological communities or natural resources. In support of the EA, studies were conducted by the F&ES Department to address the potential for impacts to water quality, marine biological communities and natural marine resources in and adjacent to Kahului Harbor as a result of the proposed improvements.

The impact studies concluded that the potential for significant impacts to regional water quality and adjacent marine communities due to the proposed Kahului Harbor improvements is small. Water quality conditions within the harbor and in adjacent open coastal waters are influenced primarily by the input of nutrient-rich groundwater and the re-suspension of sediment by wave action.

Groundwater input occurs all along the coastline, but appears to be higher than usual in the southwest corner of the harbor. Lowered salinity values and high levels of dissolved nutrients in this area demonstrate the localized source. Water quality conditions within the harbor and nearby coastal waters reflect the simple physical mixing of the high nutrient groundwater with low nutrient coastal water.

None of the proposed harbor improvements will alter the quality of groundwater entering coastal waters, or change the location of groundwater discharge.

While some sediment and turbidity may be generated by the proposed construction activities, its impact on water quality and marine communities will be small. Levels of suspended particulates in the waters of the harbor and adjacent coastal waters are primarily the result of re-suspension of bottom sediment by strong winds and/or wave action.

The harbor basin is characterized by a bottom comprised of sand and mud. Under strong trade winds, vertical mixing may bring fine sediment suspended near the bottom up into surface waters. Ship traffic, especially large ships with drafts approaching the harbor bottom depth, can re-suspend large amounts of sediment as they maneuver within the harbor.

Typical surf outside the harbor also keeps fine sediment particles suspended in a layer 1 to 2 meters in thickness above the bottom. Within this system of naturally-occurring high turbidity and suspended solids loads, the addition of small, localized sediment sources will have little incremental impact.