Climate Change: Markers set up on Stinson Beach on Saturday showed beachgoers how far up the beach the sea is expected to creep by 2100, according to an interactive model created by the county’s Collaboration: Sea-level Marin Adaptation Response Team, or C-SMART. Anyone can track projected sea level rise at   Beau Evans

At the behest of the California Coastal Commission, the county is indefinitely halting almost all new development and construction for over a third of houses in Stinson Beach, the Community Development Agency announced this past weekend, a move that changes how the county has interpreted building code for three decades.

Since 1981, the agency has permitted development along the town’s Easkoot Creek despite legal language handed down from the California Coastal Commission and codified in the county’s Local Coastal Program that clearly states no building is to be allowed in the creek’s 100-year floodplain zone. But after a contentious development proposed for Stinson, the commission clarified that development is indeed banned. The prohibition now in place will not be lifted until the county finalizes an update to the Local Coastal Program. An amendment to the program’s environmental hazards section could allow for a resumption of building in the floodplain, pending the commission’s approval—but the update won’t happen until at least next year.

“We interpreted this longstanding policy erroneously,” said Tom Lai, the assistant director of the agency, on Saturday. He spoke to a crowd of around 50 people packed into the Stinson Beach Community Chapel for a meeting held by the town’s village association on Saturday.

Mr. Lai indicated that a revised building policy in the local program might permit new construction and improvements if it could “be designed to ensure that it’s safe for 100 years.” Finalizing a draft of the pertinent amendment, however, will depend on an analysis of projected sea level rise in Stinson Beach, which is currently being compiled through a project called Collaboration: Sea-level Marin Adaptation Response Team, or C-SMART.

“C-SMART studies will be informing that [amendment],” said Jack Liebster, a county planning manager who oversees the project. “But we’ll certainly be able to update the L.C.P. prior to having all the answers to sea level rise.”

Both Mr. Liebster and Mr. Lai estimated that a draft amendment could be brought to the board for approval as early as April, though no date is set in stone.

The newly announced prohibition followed protests over a proposed development off Calle del Embarcadero. Mill Valley resident Heidi Hjorth wanted to build a 1,400-square-foot home, but it caused a stir among some neighbors, who argued that it would exacerbate flooding in an area where storms annually cause large floods from the ocean and Easkoot Creek. 

Neighbors also pointed out that the L.C.P. prohibited development in the creek’s flood zone. The county originally approved the permit because of a loophole regarding which federal agency was supposed to make the maps, but the commission recently made clear that the maps must be enforced, no matter who made them. 

Opponents of Ms. Hjorth’s plans hailed the county’s decision as a victory for homeowners affected by future creek flooding, which, they argued, would be worsened by an increase in impervious surfaces like driveways.

“I think those who own property there recognize the very serious annual flooding,” said Kathleen Hurley, one of the neighbors who appealed Ms. Hjorth’s permit application. “It was our concern to prevent the exacerbation of flooding problems to neighbors.”

Others, however, wondered whether the county had made too quick of a decision that would effect hundreds of homeowners when only one specific proposed development was in question. Barbara Boucke, who lives in Seadrift, agreed that the county’s policy on development in the floodplain should be clarified, but by a slower process than the quick-draw decision to impose a building moratorium.

“This has been the focal point of a huge brouhaha,” Ms. Boucke said. She noted that Mr. Lai had glazed over the possibility of property owners invoking “taking” rights, which would require a governmental body to provide compensation in the event that a property’s economic value is deprived due to activities such as development prohibitions.

Alongside the taking concerns, a central issue during the April appeal was whether the county should adhere strictly to insurance-related flood zones mapped by the Federal Emergency Management Agency, to which the coastal commission refers in its building prohibition. Mr. Lai said that the F.E.M.A. maps were the “best available maps and science” and that staff from the commission had insisted on sticking to the F.E.M.A. zone boundaries, which extend westward from Marine Way across the town’s “Calle” streets. Though some questioned the relevancy of the F.E.M.A. maps and asserted a general lack of confidence in the county’s ability to project sea level rise by 100 years, Mr. Lai insisted that some sort of change had to be made.

“Let’s face it: the sea is rising,” Mr. Lai said. “It’s a matter of making informed decisions now about areas where development probably shouldn’t have been built.”

The policy change excludes routine repairs and maintenance, as well as adding accessory structures such as fences and decks that would not enlarge the property’s footprint. But no additional structures or enlargement of existing properties will be permitted. Likewise, the issue of septic system installations and modifications is in limbo, as Mr. Lai advised the Stinson Beach County Water District—which is in charge of approving septic permits—to consult the county whenever a homeowner applies for a new permit. 

Finally, the question of whether a home could be rebuilt if destroyed during a future flood was not fully answered and remained in conflict with county policy, given that the current local program allows for rebuilding destroyed homes.

“You can see why we’re so concerned,” said Katie Taggart, whose insurance rates went up after her house on Calle del Pinos was flooded in December. “And we want it to rain this year!”