JOHNSTON — The town’s hopes for controlling flood waters along the Pocasset River will hinge on the completion of a federal plan due out next year.

The watershed plan will include detailed maps, specifications, and more precise estimates on the cost of improvements such as flood-containment walls along the Pocasset River, said the civil engineer who is managing the work, Frank C. Vogel, of the Natural Resources Conservation Service, a division of the U.S. Department of Agriculture.

The agency hopes to have the plan completed sometime in 2009, Vogel said yesterday.

At that point, the execution of the projects proposed in the plan will rely on the availability of federal and local funding and the follow through of town officials in Johnston and Cranston, Vogel said.

His comments on the plan follow a period of heightened concern in Johnston, where local officials had worried about the potential for storm-related flooding over the weekend. The rainfall did not cause extensive flooding.

“We were lucky because we had the rain come down heavy, then wane,” Fire Chief Andrew J. Baynes said.

The development of the watershed plan follows an earlier study that identified the construction of flood walls and the protection of wetlands as important parts of an overall effort to protect local properties from water damage.

Some of the early estimates for flood protection work included: $3.4 million for walls on Rotary Drive, at the Park Place Apartments and in the area of the Simmons Brook bypass.

Acquiring property to make room for such projects could involve some expenses, too.

At this time, NRCS does not have any money to commit to the project, according to Vogel.

Federal funding for such work would have to be allocated, he said.

Mayor Joseph M. Polisena’s five-year capital budget plan, released earlier this year, includes a $750,000 contribution for flood protection along the Pocasset River.

Yesterday, Baynes said the Rhode Island Emergency Management Agency has categorized five of the town’s dams, including structures at Oak Swamp Reservoir and Kimball Reservoir, as “having significant risk” because a breach in any of the structures would threaten lives.

The designation refers to what can happen if the dam gives way. It isn’t a reflection of the structure’s current condition, Baynes noted.

In general, the town’s topography lends itself to flooding, he said.

“We’re sitting at the base of a hill and a valley,” he said.

mreynold@projo.com