• printer friendly
• mail this article
• iPod format
• digg

Photo

Several homes on an unstable hill in the Highland Park area of Los Angeles are shown Feb. 22 afte

The mudslides caused by recent torrential rains in Southern California can be attributed in part to historic errors made back when cattle outnumbered unstable hillsides.

“Los Angeles developed as a small cow town in the lowlands, and Sunset Boulevard was nothing more than cow trails to the coast,” said Antony Orme, a professor of geography at UCLA.

As urban sprawl began to exhaust the lowlands in the 1950s, development moved to the hills.

“The problem with Southern California is the lack of management or concern for the natural system when the area was being developed,” Orme said.

Local government agencies were historically lax and lenient in providing building permits, taking a property owner’s word about the stability of a slope.

Houses were built on top of landslides that have been forgotten, but could be reactivated due to lawn watering and irrigation.

Whole communities sprang up and persist on unsafe ground. The foundations of many hillside houses are not anchored to the bedrock, and are in danger of shifting when the soil is saturated by heavy rain.

“We’ve done a lot of this to ourselves,” Orme said.

“The common public is not always very well informed, so it’s unfortunate the city and county authorities in charge of planning and developing in the region don’t take a harder line to whether an area should or shouldn’t be developed,” he said.

In addition to a past of poor building regulation, the geographic characteristics of Southern California are not cohesive to water reabsorption and the maintenance of a groundwater supply.

“Los Angeles is built on a flood plain,” said Mary Nichols, director of the UCLA Institute of the Environment.

“The entire basin was plumbed as if the goal was to get as much water out of it as possible, and when it rains it’s not well suited to storing rain water for reuse,” Nichols added.

Los Angeles rests on clay soils that inherently have poor absorption capabilities, which are only worsened by paving over with concrete or asphalt.

“It’s about as impractical a system as you can think of if you’re living in a place that’s short of potable water,” Nichols said.

But in sunny Southern California, drainage and slope stability problems often do not receive enough preventative attention until they have caused irreversible damage or tragedy.

“The hillsides around this region have soils that are very erosive – they’re always in the process of wearing down over time,” Nichols said. “Building roads, houses and driveways has caused that situation to worsen in many areas.”

Recent rains have posed more threat because soil saturation and creek bed levels have not had time to recover from last month’s showers.

This year could be the second wettest in the city’s recorded history, according to a water record that goes back to 1877.

The last time rains of comparable magnitude and inch count fell was in the El Niño season of 1997-98. The years since then have been characterized by low rainfall and periods of drought.

During dry years, the ground bakes in the sun and is more likely to crack, providing routes for water to infiltrate when it does rain.

This is what Orme refers to as the “feast or famine” phenomenon of Southern California weather, an occurrence that promotes the dangerous results of mudslides and flash floods.

“If the rain were evenly distributed throughout the whole season then it would not cause as much problems,” said geography Professor Yongkang Xue. “But instead it is very concentrated and intensive, which puts a lot of pressure on the drainage system, and causes many mudslides.”

Environmentalists and environmental agencies have been working in recent years to remedy past mistakes and prevent the vicious cycle of poor drainage and water runoff.

For example, flood control basins have been constructed in some areas. They can function as a park for picnicking in the summer months, and are closed in the rainy season to allow the water to collect and percolate back into the ground.

Individual homeowners can also take steps to take care of drainage on their property, and clear gutters to avoid water collecting on roofs and flat surfaces.

Houses on hillsides can be landscaped with plants with deep root systems, such as the Canary Island pine. The more commonly used Monterey pine, on the other hand, has a shallow root system and is very ineffective at preventing hillside mobility.

Progress is being made on the agency and individual level slowly but steadily.

“We’re a long way from a day that we can say the city is rain proof,” Nichols said.