|
| |
|
Plan Formulation |
|
The Ala Wai Canal Project
is currently in the investigation phase; therefore, project
alternatives have not yet been fully defined. The following are
concepts that are currently being considered for analysis in the
Environmental Impact Statement:
Flood Hazard Reduction Alternatives
Ecosystem Restoration Alternatives
|
|
Flood Hazard Reduction
Alternatives
The Corps has explored five types of actions in the lower portions of the
watershed that could be applied either separately or in combination to
protect Waikīkī, McCully, and Mō‘ili‘ili from the 100-year flood event.
These include:
The 2001 Ala
Wai Flood Study determined that the optimal dredge depth for the Ala Wai
Canal was between 11 and 13 feet below mean sea level (msl). Any additional
depth was found to not provide any significant increase in the Canal’s
capacity to convey flood waters. Flood walls would add capacity to the
Canal and prevent overflow into the surrounding neighborhoods.
Additionally, flood walls around the Ala Wai Golf Course could allow it to
serve as storage for flood runoff during high volume storm events.
The Canal has
a width of 260 feet downstream of its confluence with the Mānoa-Pālolo
Drainage Canal. Further downstream, that width narrows to 158 feet near the
Hawai‘i Convention Center, thus reducing its conveyance capacity and causing
water to back up upstream of the constriction. Widening the Canal at this
point is intended to relieve this problem. Additional impediments to flow
are the restrictive openings of several of the vehicle-bearing bridges that
span the Canal. Modifications to widen those openings are also being
considered.
The eight
alternatives proposed to alleviate flooding include single and multiple
actions. These alternatives are:
-
Dredging
-
Flood walls
-
A
combination of dredging and flood walls
-
A
combination of dredging, flood walls, Canal widening, bridge modification,
and Ala Wai Golf Course storage
-
A
combination of flood walls, Canal widening, bridge modification, and golf
course storage
-
A
combination of dredging, flood walls, and golf course storage
-
A
combination of dredging, Canal widening, and golf course storage
-
No action.
Evaluation of
the flood hazard reduction alternatives will take into account a
cost-benefit analysis and minimization of impacts to recreation, aesthetics,
historic and cultural resources, social resources, and native species
habitat.
|
|
Ecosystem Restoration Alternatives
Various ecosystem restoration actions are being investigated for various
stream and riparian areas of all three sub-watersheds and include:
Stream
channel reconstruction would be specifically designed to improve native
species habitat, with treatments ranging from the addition of low flow
channels to existing concrete-lined channels, to adding boulders and
meanders, to removing concrete lining, where appropriate. Riparian
re-vegetation is proposed to enhance habitat by providing natural shade,
food sources, and bank stabilization. Where stream banks require further
reinforcement measures, other methods are being investigated.
Sedimentation
basins are being explored at various locations as a way to reduce siltation
of the streams and canals. Debris catchment structures, such as booms, may
be proposed as a way to remove trash and other debris from the surface
waterways. Check dams and energy dissipation measures are proposed
throughout the mauka areas to complement the downstream flood hazard
reduction components.
Evaluation of
ecosystem restoration alternatives will be based on the area of habitat they
either create, improve, or provide access to, as well as their ability to
complement flood hazard reduction measures and minimize adverse impacts to
social, cultural, historic, recreational, and economic resources.
(Back to top) |
|
