The streetscapes of several Northwest Washington neighborhoods could be dramatically transformed under a D.C. Water proposal to deploy “green infrastructure” to prevent sewage overflows into the Potomac River.

The $100 million proposal, unveiled this week by the water and sewer utility, would modify a 2005 court-enforced mandate to build a system of tunnels to store tens of millions of gallons of stormwater and raw sewage that would otherwise be discharged into the city’s waterways during rainy weather.

D.C. Water officials say building such features as cisterns, rain gardens and permeable alleys would keep enough runoff out of the sewer system to reduce the need for storage tunnels. The utility wants to abandon plans to build one tunnel — underneath Piney Branch, a Rock Creek tributary — and scale back a tunnel planned for the Georgetown waterfront. The largest tunnel, mainly along the edge of the Anacostia River, is under construction.

The overall plan, known as the Clean Rivers Project, is estimated to cost $2.6 billion with or without the substitution of green infrastructure. The latest proposal comes after more than three years of planning that has included talks with the District and federal governments.

Changing the 2005 consent decree that mandates the storage tunnels will mean convincing the Environmental Protection Agency and the Justice Department that the new initiatives will be as effective as the tunnels. Mayor Vincent C. Gray (D) and his city administrator, Allen Y. Lew, who is also chairman of the D.C. Water board, are strong backers.

A map of the D.C. Clean Rivers Project

George S. Hawkins, D.C. Water’s general manager and the leading proponent of the changes, said green infrastructure features have been adjusted to provide the same clean-water benefits as the court-approved plan while easing anticipated water-bill hikes, creating jobs and generating additional environmental improvements.

“We’ve been fairly clear that we’re not trying to avoid or duck things,” Hawkins said, referring to the clean-water standards in the court agreement. “This doesn’t change the total cost, but it does add a little bit of breathing room for how our ratepayers get hit and when.”

Under the current plan, D.C. Water estimates that the average annual household bill would increase to $1,675 by 2032. If the proposed changes are accepted, the amount would drop to about $1,200.

But environmental advocates have been deeply skeptical of changes to the court agreement, arguing that further delays to the 20-year plan are unacceptable and that green infrastructure has not been proved to be as effective as tunneling.

Anxiety was heightened in 2012, when Gray fired his then-environmental director after the director expressed concerns to federal authorities about an earlier version of the green-infrastructure plan without clearing it with Lew.

Environmental lawyer Jennifer C. Chavez said Thursday that she had “serious concerns” about the D.C. Water plan, particularly a proposed seven-year extension to the court agreement.

“Every year that we accept raw sewage being dumped into the water of our nation’s capital is completely unacceptable,” said Chavez, a staff attorney for Earthjustice, a nonprofit law organization that represents several local environmental and community groups in a related lawsuit. “I know the time frames are long, but every year people get sick.”

The water-retention projects envisioned in the latest proposal would be constructed mainly on public property, Hawkins said, though some utility funds could be spent to provide incentives for allowing projects on private property.

The projects would be focused on two areas: the Georgetown, Burleith and Glover Park neighborhoods, whose sewers overflow directly into the Potomac; and Columbia Heights, Petworth, Brightwood and other neighborhoods whose sewage overflows empty into Piney Branch.

D.C. Water is accepting comments on the proposal through March 14 and plans to schedule public meetings for late February. Comments may be submitted to or at