Public hearings on the draft Maui Island Water Use and Development Plan start this week, with a hearing on the Kahikinui, Hana and Koolau aquifer sectors set for 5 to 8 p.m. Thursday at the Hana Community Center.

The plan provides a 20-year blueprint for all water uses on Maui and helps guide the management and use of the island’s water resources. A Maui County plan was adopted in 1990; now each island’s plan is being updated. Lanai’s plan has already gone through the process, with Molokai’s update to follow Maui’s.

Maui reportedly has enough water to supply current and future uses over the next 20 years, but water resources “are not always located in the area where they are needed,” according to the draft plan FAQ sheet. The island has an estimated 833 million gallons per day of surface water, groundwater and untapped groundwater. About 500 mgd is used on average — the vast majority by agriculture.

Water for most uses on Maui comes from groundwater wells, with a smaller portion coming from streams, or surface water. Most water for agriculture comes from streams. Islandwide, there are six aquifer sectors with a total sustainable yield of 427 million gallons per day of groundwater. (Sustainable yield is the amount of water that can be taken without depleting the aquifer.)

The six aquifer sectors of Maui island are pictured in this graphic. Maui is preparing to update its Water Use and Development Plan, a 20-year blueprint for water uses on Maui. Public hearings begin this week with a meeting on the Kahikinui, Hana and Koolau aquifer sectors Thursday evening at the Hana Community Center. Maui County graphic

The Koolau and Hana aquifers have the highest sustainable yields — 175 and 122 mgd, respectively. They also happen to be a hotbed of legal disputes over stream diversions. In June, the state Commission on Water Resource Management ordered the full restoration of flows to 10 East Maui streams for taro growing, and limited or no diversions for another seven streams to restore habitats.

The decision brought an end to a 17-year battle between Alexander & Baldwin, which had long diverted East Maui streams for sugar cane cultivation, and Na Moku Aupuni O Ko’olau Hui, a community of taro farmers, fishermen, hunters and traditional practitioners who advocated stream restoration.

Providing enough water for kalo farmers, protecting the local watershed and controlling invasive plants and animals continue to be significant issues for the East Maui regions, according to the draft plan. Kahikinui, the other aquifer sector to be discussed Thursday, covers 113 square miles and has a sustainable yield of 34 mgd.

In March, the commission also voted to set new flow levels for four West Maui streams after decades of plantation diversions — a victory for some farmers who’ve lost out on water and a worry for others who have disputed the data used by the commission. The full in-stream flow standards were expected to go into effect by the end of this year or possibly next year.

The Lahaina aquifer sector encompasses about 96 square miles from Honokohau to Ukumehame, with a sustainable yield of 34 mgd. The goals in this area include restoring stream flows to support traditional practices and revive natural aquatic ecosystems, as well as developing more basal groundwater wells to meet an expected rise in water demand from 9 mgd to 16 mgd by 2035. Population in the area was predicted to grow at the fastest rates of any of the other regions — from 24,373 in 2015 to 39,911 by 2035, a 64 percent increase.

The Koolau aquifer sector, which spans Haiku to Keanae, has the island’s highest sustainable yield at 175 million gallons per day. Maui County graphic

Meanwhile, the Central Maui aquifer sector covers the largest population center and also has the lowest sustainable yield. Spanning 229 square miles across Kahului, Paia, South Maui and parts of Upcountry, the Central Maui aquifer sector has a sustainable yield of 26 mgd, servicing a population that’s expected to grow from 103,970 in 2015 to 138,164 in 2035. The public water supply for the Central Maui sector is primarily generated from outside the area, which is why transporting water from places like the Koolau aquifer is an issue for both areas. According to the draft plan, it’s “highly uncertain” how the end of sugar operations and return of irrigation water impacts the available groundwater that can be taken from the Kahului and Paia aquifers.

Availability of water in the nearby Wailuku aquifer sector will also depend on water use permits for A&B moving forward. The sector covers 66 square miles from Kahakuloa to Waikapu and has a sustainable yield of 36 mgd. Decisions in 2010 and 2014 restored 10 mgd to the Waihee River, 2.5 mgd to the Waiehu Stream, 10 mgd to Wailuku River and 2.9 mgd to Waikapu Stream.

Following the hearing in Hana on Thursday, the next aquifers up for discussion are:

• Lahaina aquifer sector, Monday, Kaunoa Senior Center, Lahaina.

• Central aquifer sector, Dec. 4, Kihei Community Center.

• Central and Koolau aquifer sectors, Dec. 5, Hannibal Tavares Community Center, Pukalani.

• Wailuku aquifer sector, Dec. 6, Cameron Center, Wailuku.

All hearings will take place from 5 to 8 p.m. Oral testimony at the hearings will be limited to three minutes. Written comments will be accepted prior to or at the hearings.

Copies of the draft plan are available at the Department of Water Supply, fifth floor county building; at Hana, Kihei, Lahaina, Makawao and Wailuku public libraries. The draft plan also can be accessed online at www.mauicounty.gov/2051/Maui-Island-Water-Use-Development-Plan.

The final plan must be approved by both the Maui County Council and the state Commission on Water Resource Management. The plan will not directly affect the rates, fees or bills of water users, nor can it resolve legal issues under the commission’s jurisdiction.

For more information, contact Pam Townsend with the county Department of Water Supply by emailing pam.townsend@co.maui.hi.us or by calling 463-3110.

* Colleen Uechi can be reached at cuechi@mauinews.com.