News

Nicasio spillway will rise

by Ben Stocking

November 13, 2024

In preparation for future droughts, Marin Water has begun implementing a plan to raise water levels in the Nicasio Reservoir by modifying its spillway. The project is one of many being contemplated as the district implements its water supply roadmap, a document approved last year that outlines ambitious plans for increasing supply.

In the aftermath of the 2020-2021 drought, Marin Water began contemplating a variety of short- and long-term measures for increasing storage. Modifying the spillway was considered one of the quickest plans to implement because the dam was designed to allow a spillway raise. The district’s seven reservoirs hold around 80,000 acre-feet of water—roughly a two-year supply. (An acre-foot is about 326,000 gallons.) The roadmap seeks to add between 12,000 and 20,000 acre-feet of annual supply by 2035. Modifying the Nicasio spillway would add about 3,000 acre-feet, which could raise the water level by roughly three feet, according to officials.

Meanwhile, the district has postponed a decision on one of the more dramatic steps it is considering for increasing supplies: tripling the size of the Soulajule Reservoir, which could inundate 530 acres of privately owned Hicks Valley ranchland. Enlarging the Soulajule is one of three potential reservoir expansions the district is still considering.

They are also investigating the possibility of building a second reservoir in Nicasio, while a third option would expand Kent Lake, which is surrounded by district land. An engineering consultant estimated that expanding the Soulajule would cost roughly $300 million—or half the cost of the other two options. But neighboring ranchers have fiercely contested that estimate, saying it did not include the cost of buying their land.

District officials originally said they intended to announce their choice by the end of summer, but they later postponed a decision until the end of the year. At a meeting last month, they delayed their decision again, saying they expected one in the first quarter of 2025. The delay was welcomed by ranch neighbors, including Carol Dolcini, whose family has owned an 1,100-acre ranch for five generations. They say the expansion would inundate their home, their barn and 90 percent of their arable land. “Delay is always welcomed,” Ms. Dolcini told the Light. “That means they are thinking about this hard, which they should be doing. These are big projects, this is a lot of money, and there’s a lot at stake.” Ms. Dolcini hailed the Nicasio spillway project, which would raise water levels without exceeding the current storage capacity of the reservoir. “It’s reassuring to me that they are looking at these smaller projects that would provide a little bit here, a little bit there, rather than looking for a homerun. These things are within reach, and it’s nice that they are actually doing it.” In addition to Nicasio, the district is also considering spillway modifications at Kent and Alpine Lakes..