Valley of the Moon WD advances Water Supply Assessment for major Sonoma Developmental Center redevelopment

Valley of the Moon WD advances Water Supply Assessment for major Sonoma Developmental Center redevelopmentAnalytical modeling confirms that historical on-site surface water rights will provide a reliable yield of 356 acre-feet per year, safely covering the mixed-use project's demands without impacting existing municipal supplies.

The Board considered Resolution No. 260501 to adopt the Water Supply Assessment for the 945-acre Sonoma Developmental Center property.

At full buildout in 2040, the redevelopment is projected to demand 304 acre-feet per year (AFY) for 990 residential units and commercial space.

Supply will rely entirely on the site's historical surface water rights and 840 acre-feet of existing raw water storage in Fern and Suttonfield Lakes.

Modeling demonstrates a 100% reliable yield of 356 AFY across normal, single-dry, and multiple-dry year conditions.

Surplus surface water from the site could potentially be transferred to other areas of the District during emergencies.

The Valley of the Moon Water District (VOMWD) board advanced a critical water planning milestone on May 5, reviewing the Water Supply Assessment (WSA) for the redevelopment of the former Sonoma Developmental Center (SDC). The SDC Specific Plan and Redevelopment Project aims to transform the 945-acre state-owned property into a mixed-use development concentrated on a 160-acre core campus. The proposed development includes 990 residential units, 130,000 square feet of commercial and institutional space, and a 150-room hotel. According to the WSA prepared by EKI Environment & Water, the redevelopment is projected to generate a total water demand of 304 acre-feet per year (AFY) by its anticipated full buildout in 2040. Crucially, the District will not need to tap into its existing imported water from Sonoma Water or its municipal groundwater wells to support the new demand. The assessment relies on California Government Code Section 14670.10.5, which dictates that all existing riparian and appropriative surface water rights historically associated with the site remain available for the property's use. The SDC site features an independent water system historically fed by five points of diversion—including Asbury Creek, Hill/Mill Creek, Roulette Springs, and Sonoma Creek—supported by 840 acre-feet of raw water storage in Fern and Suttonfield Lakes. Analytical modeling conducted for the WSA determined that these on-site sources provide a 100% reliable yield of 356 AFY, even through single-dry and multiple-dry year scenarios. Because the 356 AFY reliable yield exceeds the projected 304 AFY demand, the WSA concluded that the project will not adversely impact VOMWD's existing customers or its long-term supply reliability. A staff memorandum noted that surplus surface water from the SDC site could potentially be transferred to other areas of the District during emergency circumstances to supplement VOMWD's collective portfolio. The board considered adopting Resolution No. 260501 to formally approve the WSA, a necessary step under California Senate Bill 610 to verify adequate long-term water supplies for large-scale developments.