The Dying of Mugu Lagoon : Report Urges Control of Silt Runoff From Upstream Erosion

Steve Schwartz pauses on a cracking concrete dock on the Point Mugu Navy base, surveying the rising salt marsh and dry land around him.

Sailors used to navigate 20-foot boats to the dock at the edge of Mugu Lagoon as late as the 1960s. But just recently, Schwartz and another Navy ecologist ventured out in a shallow-draft canoe; “we bottomed out,” Schwartz said.

An estimated 240 million tons of sediment sweep into Mugu Lagoon every year, building up sand bars for lolling harbor seals and resting shore birds where there once was deep water.

The tiny grains of sand and silt are carried by runoff down a web of creeks and arroyos that fall from the hills above Simi Valley, Moorpark, Camarillo and Thousand Oaks.

A recent report on the 343-mile Calleguas Creek watershed says the accelerating flow of fresh water and sediment threatens the habitat of endangered and other rare species in Southern California’s largest remaining salt marsh.

The infusion of fresh water decreases salinity, killing some fish adapted to salt marsh, the two-year study says. It also carries pesticides from farms upstream and urban pollutants.

The accompanying sediment is burying eelgrass beds that provide a nursery for fish, the report says, and it is covering a delicate ecosystem under tons of mud and sand.

“With the loss of wetlands elsewhere, this area takes on an increasingly important role for migratory birds as a stopover on the Pacific Flyway,” said Sheri Klittich, a soil conservationist with the Natural Resources Conservation Service of the U. S. Department of Agriculture.

Mugu Lagoon also provides food and shelter to the endangered American peregrine falcon, California least tern, light-footed clapper rail and California brown pelican, the report said. In addition, it is one of the few remaining places in Southern California where harbor seals pup.

The report, written by Klittich’s co-workers with help from local, state and federal officials, suggests a variety of tactics to control farmland erosion.

It also recommends that county flood control officials build concrete and earthen structures, including a major catch basin just upstream near Pacific Coast Highway, to capture the sediment before it pours into the lagoon.

The report acknowledges that it cannot determine exactly when Mugu Lagoon would be filled, given the influence of ocean tides and other factors.

Yet it cites an earlier study that projected most of the area will rise to five feet above sea level in about 40 years, shrinking the lagoon to a fraction of its present size.

Schwartz, who helps lead a team of Navy biologists, is not so sure about the imminent doom of the wetlands.

He sees another force of nature at play: A deep canyon in the ocean floor has started sucking away the Navy base’s shoreline like a huge sinkhole. The 300-foot-deep marine canyon, which stretches miles off the coast, has starting moving inland.

It has already gobbled up the 200-foot-wide beach that used to protect the base’s old officer’s club and other recreational facilities on a spit of sand between the ocean and Mugu Lagoon.

Navy crews have chopped off the end of the pier that slumped into the canyon. Now a huge rock seawall protecting Navy buildings has begun to slide into the submarine trench. Schwartz said the Navy plans to retreat from the advancing ocean, demolishing two buildings standing in its way.

Preliminary studies predict that the canyon will continue to eat away at the spit until the ocean connects with the lagoon within 20 to 40 years, Schwartz said. “When that happens, it could end the sediment problem.”

The flow of silt and sand is as old as the Oxnard Plain itself.

Sediment has washed down these creeks and the nearby Santa Clara and Ventura rivers for eons, fanning out across the Oxnard Plain to deposit a rich layer of topsoil.

The river of sediment picked up speed during World War I, when farmers uprooted native vegetation on hillsides around Camarillo to make room for rows of lima beans, the report said.

The accelerated erosion helped carve the barrancas and gullies that can be seen cutting into the hilly terrain today.

Before 1862, no defined channel connected the creek runoff with Mugu Lagoon.

By 1889, residents had cleared a straight channel along a portion of Calleguas Creek. Over the years, the channel was lengthened and improved to minimize flooding and steer runoff directly into the lagoon.

The Navy dredged the lagoon in 1946, but neither the report nor Navy officials suggest doing that again.

In addition to the immediate disruption of wildlife, dredging could stir up DDT and other agricultural pesticides and pollutants that have poured into the lagoon over the years.

“If you have a layer of DDT or heavy metals five feet down, you’d just mix it up in the water and expose endangered birds and species again,” Schwartz said. “Right now, it is more or less entombed.”

Without the option of dredging the lagoon, soil conservationists have focused on solutions upstream along the 36-mile-long Calleguas Creek, which has three different names.

It’s called Arroyo Las Posas in its middle section and Arroyo Simi to the east, where it wends through Moorpark and Simi Valley. The creek’s tributaries include Conejo Creek, Arroyo Santa Rosa, Beardsley Wash / Revolon Slough and dozens of streams throughout the watershed that is 30 miles long and 14 miles wide.

In recent decades, ranchers have cleared additional steeper, sloping land in the watershed to plant avocado orchards and citrus groves, particularly in the hills around Camarillo and Moorpark.

The denuded slopes and access roads have increased the runoff, as have increased housing and commercial developments. The increased velocity of the waters scours the gullies and barrancas as the runoff heads to the creek on its way to Mugu Lagoon.

In a moderate storm expected every two years on average, suburban development and farmland cultivation has increased runoff by about 20%. And with it comes a heavier load of sediment, which boosts the bulk of the flow and its erosive power.

To slow the trend, the Natural Resources Conservation Service, formerly the Soil Conservation Service, has been working with farmers and other landowners to plant cover crops on newly disturbed land.

It offers advice on building small structures in stream beds and planting vegetation to slow the flow of runoff in gullies.

In the report released earlier this month, soil conservationists also recommended that the county pursue plans to build a sediment catch basin as part of improving lower Calleguas Creek.

Alex Sheydayi, deputy director of public works, said the planed basin on Calleguas Creek near Pacific Coast Highway is an important part of rebuilding the channel to prevent a recurrence of flooding, such as the widespread inundation of prime farmland in March, 1992.

“We are optimistic we can pull something off in the next five years,” he said.

The report also suggests giving the public better access to Mugu Lagoon, which can be visited now only with special permission from the Navy.

Mugu Lagoon “has a real identity problem,” said Peter Brand of the state Coastal Conservancy, which provided a $100,000 grant to help with the $256,000 report. He suggests that it would have broader public support if it becomes better known.

Schwartz said the base’s environmental office is working on a plan to create a special gate so that the public can visit the wetlands without needing to penetrate the shield of tight naval security elsewhere.

Protected wetlands and salt marsh make up 2,500 of the base’s 4,490 acres, and much of the fragile area is separated from the buildings reserved for missile tests and other secret work.

“There are some peaceful spots out here,” Schwartz said, scanning the wetlands from the old boat dock. “You’d never know you were on a Navy base, until an F-14 screeches by.”