East Maui in historic drought: flows at record lows, county turns to wells and storage planning

Commission staff presented a multi‑hour briefing on Oct. 28 summarizing hydrologic records and ecological monitoring across East Maui and describing consequences for municipal water supply and agricultural diversion during the 2025 drought.

Key hydrologic findings presented by staff included examples of steep declines in modern flow statistics compared with earlier climate windows: at one continuous‑record station the recent median (Q50) was 8.9 cubic feet per second (CFS) compared with an earlier Q50 of 14 CFS for the 1984–2013 period; several gauges showed Q75, Q90 and Q95 values substantially lower in the most recent three water years. Staff said some gauges recorded prolonged periods of all‑time low flows during 2025, and that USGS gauges in the upper watershed recorded near‑zero readings at times this year. Multiple named streams (Makapipi, Pāʻinaʻau, Honomanū among others) were described as having very limited or no flow in recent months; Makapipi was reported dry much of the year.

County response and operational detail: Staff and Maui Department of Water Supply (DWS) described how low ditch deliveries required DWS to rely more heavily on groundwater wells (the Hamakua Poʻokō wells were brought online) and to increase production at the Kamōle water treatment facility to meet upcountry demand. Aaron Scott summarized an existing memorandum of understanding between East Maui Irrigation (EMI) and Maui DWS that sets prioritization and sharing when ditch flows are low; staff said DWS has generally continued to take the water it needs for potable supply and that some irrigation water deliveries were curtailed when flows dropped.

DWS perspective: John (Maui DWS) told the commission the county is pursuing multiple measures to improve reliability, including replacing filters at the Kamōle treatment plant to expand capacity, designing two reservoirs at the Kamōle site with a combined capacity of about 140 million gallons, and seeking federal funding for construction. John said estimated capital costs for reservoirs are on the order of $25 million and that DWS’s existing capital budget is constrained.

Ecological monitoring and implications: Staff reviewed biological monitoring of streams that have different restoration designations (full restoration, H‑90 partial restoration, connectivity flows). Some streams with substantial groundwater gains downstream (for example, Hanaʻōʻī‑type examples discussed by staff) showed unexpectedly robust recruitment of amphidromous species despite only connectivity flows being in place; other streams showed lower diversity and abundance and evidence of low dissolved oxygen and non‑native species impacts in estuaries. Staff cautioned that monitoring capacity is limited; their datasets are valuable but not sufficiently frequent to capture all seasonal population dynamics.

Public testimony and stakeholder concerns: Multiple community representatives, conservation groups and kuleana holders testified. Points raised included ongoing community observations of dying vegetation and reduced stream flow, concern that Mahi Pono’s agricultural expansion could increase pressure on sources, requests for better and transparent real‑time monitoring (including midpoint transition‑zone groundwater measures and chloride sampling), and calls for the commission to coordinate more closely with DHHL, the Board of Land and Natural Resources, and county planners on reservations and long‑term allocations.

Staff comments and follow‑up: Commission staff said existing monitoring and recent studies give a stronger, updated hydrologic picture than earlier reports, but that datasets and staffing remain limited. Staff recommended identifying contingency options (capture high flows for storage, larger reservoirs, temporary adjustments to non‑drinking off‑stream allocations under extreme drought) and said any changes to in‑stream flow standards would require careful legal and ecological review. Commissioners asked staff to continue updating drought‑era statistics, to coordinate with DWS on storage and demand options, and to keep the commission apprised if the county requests emergency action.