King County officials hammered home the message Tuesday that Green River Valley residents and business owners need to prepare for flooding with the Howard Hanson Dam not operating at full capacity and with forecasts for a La Nina winter.

La Nina weather systems occur when the temperatures of the Pacific Ocean near the equator are colder than normal, which could mean more rain and snow in these parts. La Nina is the counterpart of El Nino, when ocean temperatures are warmer than normal and lead to warmer and dryer winters.

“We are very concerned that people will be complacent because of the mild winter that we had last year,” said Christie True, county Department of Natural Resources director, at a media conference Tuesday in Seattle. “We really need to get ourselves back into thinking like we were a year ago when we could have had really extensive and severe flooding.

“The better outcome is to be prepared. If we don’t have (flooding) that’s great. But if we do have it, you’re going to do so much better protecting your family and your home and property if you really do prepare for the worst. That’s what looking at right now.”

County Councilwoman Julia Patterson, whose district covers much of the Green River Valley, remains confident residents know the threat of flooding exists. But Patterson has concerns about the forecasts for a La Nina winter.

“It could be a very wet one because of the most intense La Nina since 1955,” Patterson said.

Patterson also knows there is a chance weather forecasters could be wrong.

“Mother Nature is tough to predict,” Patterson said. “There’s no way of really knowing what Mother Nature is going to do. We are better prepared this season. But it is important that we are all ready for flooding.”

County leaders are concerned about a wetter than normal winter because the damaged Howard Hanson Dam cannot hold back as much water as its original design stipulates. Heavy rainstorms in January 2009 damaged the abutment next to the dam. that was built in 1961 to help protect the Green River Valley from flooding.

The U.S. Army Corps of Engineers, which oversees operations of the Hanson Dam, has lowered the threat of Green River flooding this winter to 1 in 60 from 1 in 33 last year because of installation of a grout curtain. But the odds of flooding are 1 in 140 when the dam is fully operational. All of the additional repairs to put the dam at that level are not expected to be completed until 2012.

Many residents took steps last year to buy flood insurance, sign up for emergency alert messages, prepare an emergency kit, know an escape route and even protect their property with sandbags or a flood wall.

Crews from King County and the cities of Kent, Auburn, Renton and Tukwila worked to install thousands of giant sandbags along the Green River to help protect homes and businesses from flooding.

Crews inspected the 26 miles of sandbags this fall and replaced about 250 bags because of vandalism or bags that had degraded. But now the bags are back to standard, said Mark Issacson, county director of the Water and Land Resources Division.

Despite the efforts by the county, cities and corps, however, County Executive Dow Constantine emphasized residents need to stay alert this winter.

“The temporary flood prevention measures that are still in place and repairs at Howard Hanson Dam appeared to have passed all of the necessary tests,” Constantine said. “This is good news for our Green River Valley residents and businesses. But this is not a signal for any of them or any of us to let down our guard. It remains vitally important to make sure we are all ready to deal with flooding.”

King County has operated a flood warning center for 50 years and that center is prepared to take on this winter if forecasts call for heavy rains. County levee inspection teams check the Green River 24 hours a day.

“We do send out teams to inspect and to look for weak spots that might occur,” Issacson said. “They report to our flood warning center and we get that information out to our cities, residents and emergency crews.”

The flood warning system provides at least two hours notice before floodwaters reach damaging levels. The flood warning center only opens during rainstorms. Residents can call the center directly during storms with their flooding concerns and questions at 206-296-4535

For more information about flood preparation, go to www.kingcounty.gov/flood or call 206-263-3400.