FLOODING COULD FOLLOW FALL'S FIRES SEDIMENT FROM HEAVY RAINS COULD CLOG DRAINAGE CHANNELS.

Byline: Eric Leach Staff Writer

SIMI VALLEY - Although the city escaped serious flooding during the near record rains earlier this year, the coming rainy season has officials concerned because of possible water and mudflows off the thousands of acres of land burned over in the Topanga Fire.

Officials said one area of particular concern in Simi Valley as a result of the Topanga Fire is Meier Canyon, which runs through Brandeis-Bardin Institute and out to the Arroyo Simi by the Arroyo Simi Equestrian Center.

Another concern is Bus Canyon, which drains to the Arroyo Simi at the west end of the city.

``If what happened last year in the Santa Clara River happened in Simi Valley, there could be severe problems. Simi Valley got off pretty light last year,'' said Mark Bandurraga, the hydrology section manager at the Ventura County Watershed Protection District.

Flooding along the Santa Clara caused serious problems from the storms earlier this year, including closure of portions of state Route 126 and destruction of part of the runway at the Santa Paula Airport.

Just west of Simi Valley, 80-year flood conditions were reached in the Happy Camp Canyon, an area burned in the 2003 brush fires.

The 2003 fires also led to a gigantic buildup of silt and debris behind the Las Llajas Dam, which protects Simi Valley from flooding. This made it necessary this summer to launch a multimillion-dollar cleanup effort with hundreds of trucks to remove the muck behind Las Llajas Dam.

Now officials are concerned the same kind of thing could happen as a result of the Topanga Fire if the area is hit by heavy rainfall.

The Topanga Fire broke out Sept. 28 and burned from the Rocky Peak area along the Ronald Reagan (118) Freeway at the east end of Simi Valley along the Simi Hills, eventually consuming about 24,000 acres to the outskirts of Old Agoura.

``You don't know where the intense rains are going to occur,'' Bandurraga said. ``Last year we had intense rainfall in Happy Camp Canyon. ``Since we don't know (where bad weather might hit) we have to cover all of our bases and try to protect everybody as best we can.''

If there is heavy rain there will be an increase in runoff and an increase in sediment that can clog up the channels meant to keep flooding water out of homes and businesses in the city.

``Las Llajas is a good example of that happens after a fire,'' Bandurraga said. ``If a detention basin fills up with sediment, it can't reduce the flows of water as it is designed to do.''

Flood control officials say they are working as fast as they can to visit the burned over areas and calculate the potential runoff of water and sediment. They say it might be necessary to build small dams and temporary flood control basins in response to the potential danger until plants can grow back on the hills to help anchor in the soil.

Bandurraga said besides Meier and Bus canyons, officials are also concerned about the fire's impact on Lang Creek that drains from the burned out area to Thousand Oaks, but new debris and water detention basins should help reduce any heavy flows there.

On the south side of the Simi Hills officials are concerned about canyons that drain into Malibu Creek.

Christopher Stone, principal engineer of the water resources division of the Los Angeles County Department of Public Works, said officials are assessing the potential for flooding and will be taking steps to protect homes and businesses that might be threatened.

``We are always concerned about the debris and mud flows that can be anticipated after a fire,'' he said.

``If we think sediment and debris might impact houses and businesses, we might put up some kind of structure to remove the sediment and debris, some type of barrier to catch that material.''

He and others said it's impossible to know what exactly will happen because it all depends ultimately on the intensity of the rain.

Woody Smeck, superintendent of the Santa Monica Mountains National Recreation Area, said officials are hoping the first rains this fall will be mild and start the process of regrowth on the blackened hillsides.

``We are very concerned about flooding and are working with the Ventura County Watershed Protection District on actions to stabilize slopes. Hopefully Mother Nature will cooperate and give us moderate rains at first to germinate the seeds to anchor soil,'' Smeck said.

``We are assessing the situation. It is the surface area that is of concern right now. If there are heavy rains the soil could wash down into the streams and we will certainly take action to prevent that.''

Eric Leach, [phone]

eric.leach(at)dailynews.com