An investigation into the cause of flooding that damaged houses and yards in the Fauntleroy neighborhood last winter indicates numerous problems cascaded into each other.

Last December's flooding occurred around California Drive south of the Fauntleroy Ferry Terminal. Many of the streets in the neighborhood remained unpaved and without drainage until the 1960s and '70s, said Sahba Mohandessi, project manager for Seattle Public Utilities. When California Drive and neighboring streets were finally paved, they did not get curbs, gutters or subsurface reinforcement. The roads got only a layer of asphalt and a layer of small-size gravel pressed into it. Called "chip sealing," it's the most economical paving method. California Drive was last repaved 10 years ago.

Some catch basins were installed in the streets but, over the years, repaving changed the way rainwater flows. Now much of the runoff never reaches the underground drainage system, Mohandessi said.

There are other problems too.

Catch basins and drainage pipes were found to be clogged with beauty bark and other landscaping materials. RoseWater Engineering, a consulting firm hired by Seattle Public Utilities, discovered that a nearby hillside had been covered with a plastic material with a layer of landscaping bark on top. Last December's heavy rainfall washed the bark off the plastic and into neighborhood drains.

Inspecting engineers also found lots of sediment caked inside the neighborhood's drainage pipes.

Obstructions in the pipes let so little runoff water into the drainage system that there isn't enough water to scour the inside of the pipe. So the drainage system is actually operating below capacity.

Another problem with the neighborhood's overall drainage system is that many of its parts that were built and paid for by individual property owners haven't been taken care of properly.

"Some private systems must be maintained more vigorously," Mohandessi said.

Many people don't realize it is their responsibility to keep some parts of the drainage system on their private property in good operating order, said City Councilman Tom Rasmussen. He attended a public meeting last week at the Southwest Branch of the Seattle Public Library to discuss the Fauntleroy flooding problem. About 35 people attended.

Underlying all the other factors that contributed to the flood is the fact that the hillside east and uphill from California Drive oozes spring water year-round. "It's already naturally saturated," said a man at the meeting.

Seattle Public Utilities is now presented with four options for fixing the problem. Each proposal includes molding 3-foot-long berms in road asphalt along with shallow channels to direct rainwater to existing catch basins, Mohandessi said. That would cost an estimated $16,000.

The other options each add to the berms and channels. Option 2 recommends replacing the storm pipes, catch basins and a sandbox filter at a cost of about $264,000.

Option 3 would include resurfacing affected streets for $183,000.

The most expensive option - $380,000 - would build regular streets with curbs and gutters. It would replace all drainage pipes and install an underground holding tank to capture the flood and expel the water at a slow rate.

Some people recommended installing a bigger combined sewer overflow pipe to drain the neighborhood quicker. But that could simply move the flooding problem to another neighborhood.

"We can't make something worse for somebody else," Mohandessi said.

Tim St. Clair can be reached at 932-0300 or timstc@robinsonnews.com