The Palo Alto City Council agreed on Monday night to explore a new law that would prohibit construction within 150 feet of streams and rivers.

The policy, which specifically targets the riparian corridors in the rural part of the city west of Foothill Expressway, came out of a set of recommendations from the Citizen Advisory Committee, a group that is helping the City Council revise the city's Comprehensive Plan.

On Monday night, the council approved with two unanimous votes the Safety and Natural Environment chapters (known as elements) of the plan, a broad document that will serve as the city's guide on land-use issues until 2030.

Many of the programs and policies in the new Natural Environment element are similar to those in the existing plan, with a strong emphasis on protecting open space; improving the urban forest; limiting noise; and ensuring clean air and water. One broad change between the existing document, which was adopted in 1998, and the new one is the inclusion of "climate change and climate adaptation" as a goal in the new version.

In a nod to more local concerns, the Natural Environment chapter also includes new programs relating to reducing airplane noise, enforcing of the leaf-blower ban and working to evaluate California's proposed high-speed-rail system. But the program that attracted the most attention Monday night was the one dealing with riparian corridors.

The Citizen Advisory Committee, which helped write much of the element, split between those members who believed that the limit should be expanded from 50 to 150 feet and those who wanted to further evaluate the issue before settling on a specific number.

Don MacDougall, a member of the citizen committee's Sustainability Subcommittee, is in the former camp. He called a 150-foot setback the "absolute minimum" and urged the council to adopt the program.

Shani Kleinhaus, also a member of the citizen committee, agreed and noted that other cities in the county, including San Jose and Mountain View, have recently moved to increase setbacks in sensitive habitats. San Jose adopted a 100-foot setback near its riparian areas while Mountain View created a "habitat overlay zone" in the North Bayshore area, prohibiting development within 200 feet of the riparian corridor. Santa Clara County has adopted a setback of 150 feet.

"Every time we plan and build too close to creeks, there are externalities that come to haunt us," Kleinhaus said. "We already see issues with flooding and with having to reinforce and concretize creeks not only in Palo Alto but everywhere."

The policy proposal quickly won over the council, with Vice Mayor Liz Kniss and Councilwoman Karen Holman quickly endorsing it. The only debate was whether the council should simply add a policy for the 150-feet setbacks or whether it should direct staff to explore it. The council ultimately chose 6-3, with Holman, Eric Filseth and Lydia Kou dissenting, to go with the more cautious language.

This quibble notwithstanding, all nine council members agreed that the updated Comprehensive Plan should include stronger protections for local creeks and streams.

"We have no idea what will happen next year -- a drought or a flood yet again," Kniss said. "Because this is a very uncertain environment, I'm going to suggest that 150 feet would be a desired stream-setback metric."

Holman concurred and said adopting the new setback requirements would place Palo Alto among the leaders in the realm of habitat protection. While Mayor Greg Scharff and the council majority were hesitant about adopting a specific number without further analysis and more public input, Holman had no such hesitations.

"It's what other cities in the county are doing and it's what the county is doing," Holman said. "I think it's quite appropriate."

The new program directs staff to explore expanding the setback along local rivers and streams to prohibit siting of buildings, impervious surfaces, outdoor activity areas and ornamental landscaped areas within 150 feet of the creek bank.

The new Comprehensive Plan program will not, in itself, establish the setback requirement along riparian corridors. It does, however, pave the way for the council to create an ordinance that would achieve the restriction. Planning Director Hillary Gitelman told the council that adopting such laws can be a complex endeavor.

"You're telling property owners that there is a section of their property that they may not be able to improve as they may wish to," Gitelman said.

The council also unanimously approved the Safety Element, which is built around the goals of risk prevention; protection from natural hazards and disasters; and human-caused threats. Council members were also scheduled to review the Business Element but agreed to delay that discussion until May 22.