A massive environmental review of a project aimed at protecting people and property along urban streams and the Ala Wai Canal in the event of a 100-year flood is still two years from being released. But residents have a chance this month to weigh in on the flood impacts and mitigation measures officials are studying.

The draft environmental impact statement for the Army Corps of Engineers' Ala Wai watershed project is expected to be released in winter 2010, opening the door to tens of millions of dollars in federal funding for flood-mitigation efforts in urban Honolulu.

The Ala Wai Canal is the major priority of the project, since a 100-year flood in Waikiki could cause hundreds of millions of dollars in damage and cripple the state's economy.

But the study will also look at long-term mitigation efforts for streams in Manoa, Makiki, Palolo and elsewhere.

At a community meeting on Oct. 21, residents will be asked for their input on the flood concerns in their neighborhoods and possible flood mitigation options. Cindy Barger, program manager for the Army Corps study, said the meeting will also help officials identify priorities for work — beyond the Ala Wai Canal.

The Army Corps study was originally supposed to only look at ways to minimize the impacts of a 100-year flood of the Ala Wai Canal. But the study was broadened to include streams that flow into the canal after massive flooding four years ago in Manoa, which caused millions of dollars in damage to several homes and University of Hawai'i-Manoa labs and buildings.

The expanded project, Barger said, is meant to study the watershed in a holistic way by looking at water availability, when flooding happens and pollution problems.

Flood mitigation efforts under review in the study include everything from restoring habitats to dredging to constructing higher walls around urban Honolulu streams. Barger said the final environmental impact statement on the mitigation efforts will be released in early 2011. Construction is expected to start two years later.

Flood efforts would be completed in phases, and work could go on for a decade or more.

A 100-year flood has a 1 percent chance of happening in any given year.

Officials have said a major hurricane could spur such a flood — through a combination of rainwater from mountains and storm surge — sending up to 7 feet of water into densely-populated areas of Waikiki and McCully.

So far, as part of its study, the Army Corps has been examining the existing conditions in the watershed. The review comes as the city and state are looking at short- and mid-term possibilities for flood mitigation in the urban core. The state, for example, is studying mid-term flood mitigation measures at Woodlawn Bridge in Manoa, where water topped its banks on Oct. 30, 2004, rushing into homes and University of Hawai'i buildings.