City officials say unusual weather, not inadequate storm drainage to blame for flooding

City officials say unusual weather, not inadequate storm drainage to blame for flooding
Courtesy: Randall Pasion
Courtesy: Randall Pasion

HONOLULU (HawaiiNewsNow) - For the second time in one week, downtown Honolulu and Ala Moana area parking garages filled with rainwater as heavy thunderstorms rolled through Wednesday.

The flooding conditions have residents questioning whether Honolulu's storm drainage infrastructure is failing, but city officials maintain the storm drainage system is performing as it was designed. They say it hasn't been able to sustain the level of rain that has fallen in the past few days, not because it doesn't work properly -- but because the weather patterns have been so unusual.

"It can't handle all storm situations, but for the most part it handles most of the storm related water that we receive and that's the reason why we don't see this level of flooding all the time -- it's something that's really uncharacteristic," said Ross Sasamura, the Director and Chief Engineer of the City and County of Honolulu's Department of Facility Maintenance.

Experts with the National Weather Service agree.

"Having this sort of intense rain event over Honolulu -- that amount of rain in that period of time is something on the order of 10 - 15 year storm," described Chris Brenchley, an NWS meteorologist.
Brenchley says models indicate four and a half inches of rain fell over the Aloha Tower Marketplace in just 3 hours on Monday. During the same time period Wednesday, another two inches of rain dumped on the area -- leading storm drains to overflow and geysers to explode from manhole covers in downtown Honolulu.

City officials say the fact that streets don't remain continuously flooded within half an hour of the rain stopping indicates the storm drain system is working, it was just temporarily overwhelmed.

"I wouldn't say that the storm drain system isn't properly moving the water away. There were certain design guidelines that the system was actually
constructed with. The fact that we have localized heavy rains is not an indication of the suitability of the storm drain system -- it's merely an indication of how much rainfall we're receiving in a specific location at a specific time," said Sasamura.
City officials say residents shouldn't grow accustomed to wading around in rainwater, but they should be prepared for that possibility when the grounds are as saturated as they have been and more thunderstorms are in the forecast.
"I think what we need to know is whether these weather patterns are to be expected continuously. If we have these types of rains every week for a whole year and we expect that pattern to continue for another 50 years, we'll have to make adjustments -- but until that time, the costs and the impact to the public to re-do the entire drainage system -- right now, would be prohibitive," said Sasamura. 
They say they have been routinely checking the catch basins where debris collects after significant rainfall to ensure that nothing is obstructing the storm draining system and they will continue to monitor the situation as they keep an eye on the next system that is rolling in.

Copyright 2015 Hawaii News Now. All rights reserved.