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.