Manoa a flood-plan candidate

Officials are studying factors in the Halloween-eve flood in Manoa Valley to determine whether to add the valley to a $1.5 million federal flood-control plan for the Ala Wai Canal and Waikiki.

Among the concerns are the dense development of Manoa Valley, low bridges that easily catch debris, and "pinch" areas where a bridge or concrete stream channel forces floodwaters into a narrow area, said Derek Chow, an engineer with the Army Corps of Engineers.

More than 10 inches of rain fell in the upper Manoa Valley over a 12-hour period Oct. 30-31, causing extensive flood damage to more than 100 homes and numerous University of Hawaii buildings. Damage estimates are not complete, but are in the millions.

The current Ala Wai Canal Project being planned to lessen the impact of flooding in portions of the Ala Wai Watershed (Manoa, Makiki and Palolo valleys) is makai of the H-1 freeway, Chow said.

But the recent flooding in the mauka portion of Manoa Valley has state and federal officials wondering whether to add the upper Manoa, Makiki and Palolo valleys to the flood-mitigation plan, Chow said yesterday.

The Ala Wai project as currently envisioned includes ecosystem restoration projects in the upper valleys, but not flood-control measures, he said.

Potential solutions, if the areas were added, could include widening or changing bridges, shoring up eroded areas, and building detention basins to store water, sediment and debris during intense floods.

Meanwhile, Gov. Linda Lingle declared the entire island of Oahu a disaster area yesterday due to "multiple periods of heavy rains and flooding beginning Oct. 30 through Nov. 7."

Lingle's original proclamation specified Manoa Valley, which was hardest hit by flooding Oct. 30-31. But the supplemental proclamation will enable flood victims and properties in other areas to receive federal aid, a statement from Lingle said.