HALEIWA (HawaiiNewsNow) - When heavy rain hits the North Shore, the water that runs under the Joseph P. Leong bridge in Haleiwa is a serious concern for people who farm the land and live in the homes downstream.
Katherine Kawamata's Haleiwa property has been flooded twice. The last time was in December of 2008.
"What are you going to do? The water just keeps rising," she said.
The same storm shoved water and mud into scores of homes that line the waterway that runs from Haleiwa to Waialua after passing under the bridge.
In 1974 a flood killed three people and did a mountain of damage.
Other heavy rains have also lifted the stream over its banks.
Now North Shore residents have a new warning system a computer click away. It's called a radar pulse sensor.
"What we wanted to come up with collaboratively between the USGS and us for the residents in that area was something that can provide them data all year long," Hawaii State Civil Defense Vice Director Ed Teixeira said.
The state bought two sensors that look like television antennas attached to metal boxes and mounted them to the bridge.
The instruments use satellite telemetry to measure the stream's height. They shoot the information to a satellite. The data is then sent to the U.S. Geological Survey's Water Alert web site.
People in the flood zones can now monitor the height of the stream by signing up at the site. They can set their own threshold level - the state recommends five to seven feet.
When the stream hits that height, subscribers to the alert receive a warning.
"The alert system can then trigger their telephone, computer, cell phone to let you know, 'Hey, it's been raining, You do have a flash flood warning in effect by the weather service and now it's measuring seven feet.'" Teixeira said.
The sensors give residents in the flood prone areas of Haleiwa and Waialua instant information that can help them decide when to evacuate, even ahead of Civil Defense warnings.
The USGS and State Civil Defense will make a presentation on the sensors at the North Shore Neighborhood Board meeting Thursday at 6:30 p.m. at the Haleiwa Shingon Mission at 66-469 Paalaa Road.