Catch-Basin Cleaners Caught Short by Storm

The rain that pains is what gathers in the lanes.

Traffic lanes.

As is often the case, the San Fernando Valley got hit with more rain than the rest of the city--3 inches in Thursday’s storm contrasted with 0.77 of an inch that fell on downtown Los Angeles in the same period, according to the National Weather Service.

And the storm hit at a particularly poor time for the crews who clean out the catch basins that carry rainwater away from streets.

They had not yet started work for the year.

“Usually, the first storm of the year is when you find out that some catch basins are clogged by debris and leaves, and that’s why you get flooded intersections,” said Pat Howard, director of street maintenance for the city Department of Public Works.

Although the city has 16 people assigned to cleaning catch basins year-round, “most of their work is in response to complaints,” said Ray Jellison, supervisor of waste-water collections systems. For two months each year, the city provides funds for an extra 40 people to conduct the annual clean-out of catch basins.

The special crews work from Oct. 15 to Dec. 15 in order to finish just before the rainy season begins, he said. The crews had barely reported for work this week when the storm hit, Jellison said.

Still, he said, only about 5% to 10% of the 15,000 to 20,000 catch basins in the Valley clog during the dry season, and most of those have backups close by.

In older Valley neighborhoods, those developed in the late 1940s and 1950s, streets are often drained by culverts that clog easily, he said. Newer areas have storm drains with greater capacity.

Topography Is Problem

There are still many proposed storm drains awaiting financing, he said, “but the system is certainly in better shape than it was in past years.” In the 1920s and 1930s, floods caused widespread damage in the Valley.

The basic problem is the Valley’s topography--”a large flat area surrounded by hills,” Howard said.

The nearby mountains also cause heavier rain than falls on the comparatively flat land to the south in the Los Angeles Basin.

Meteorologist Kerry Emanuel, an associate professor at the Massachusetts Institute of Technology, studied the phenomenon when he was on the UCLA faculty during the series of disastrous storms of February and March, 1980.

As moisture-laden air moves toward the Valley from the ocean, it must cross the Santa Monica Mountains, which give off rising air currents. Because air is colder at higher altitudes, the moisture in the rising cloud condenses into rain.

He said he originally expected to find the heaviest rain falling just downwind from the highest points of land, but, in recent years, “colleagues have pointed out to me that what is going on is more subtle.”

“There are clouds at altitudes high enough that they don’t feel the effect of the mountains,” he said. “They cause a steady light rain everywhere. However, those raindrops fall through lower clouds,” which have been shoved upward and cooled by the mountain slopes.

“The thicker the clouds those raindrops fall through, the more collisions there are with water droplets in the lower cloud. The drops get bigger and bigger, in a snowball effect.

“Thus, there is rain falling from a high altitude over a wide area, which is uniform. But it is falling through clouds at lower altitudes which are not uniform, getting thicker as it falls, and so the rain is heavier over the mountains.”