Waimea Valley park workers and lifeguards helped city workers Wednesday quickly dig a channel by hand through a sand berm built up from heavy surf to alleviate flooding from the fast-rising Waimea River on the North Shore.

About 100 people in Waimea Valley were evacuated after Waimea River overflowed, flooding the roadway into the park with 2 feet of water.

Waimea Valley Executive Director Richard Pezzulo said he called the city Wednesday morning when the swollen river began rising rapidly. The city workers arrived in about an hour, armed with shovels.

Officials said the combination of rain and ocean swells blocking the river caused the flooding.

Pezzulo said the city planned to send workers back today with heavy equipment, but park and city workers dug a 2- to 3-foot-wide channel and the “water flowed through digging its own way out.”

Shayne Enright, spokeswoman for the Department of Emergency Services, estimated the channel grew to about 20 feet wide and 15 feet deep.

“It was really unusual that it came up so fast,” Pezzulo said.

Ocean Safety personnel posted warning signs about noon Wednesday at the mouth of the river, which was flowing quickly and carrying debris into Waimea Bay. “We actually saw a television set in the water,” said Enright said.

National Weather Service lead forecaster Sam Houston said it has been an extremely dry fall through December, but some Koolau Mountain gauges showed nearly 6 inches of rain in 24 hours ending at 5 p.m. Wednesday. Because of unusual swells, more sand was pushed up on shore blocking the river, he suggested.