Big Creek Slide of March 2000

March 2000 - May 2002

(see after June 2002 page for recent monitoring and progress)

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Background A landslide buried Highway 1 on March 12, 2000. The slide was approximately 500' long and 100' wide, and crossed the highway and continued down to the beach. CalTrans repair crews and private contractors immediately began efforts to clear the slide as well as to plan for disposal of the slide material. Negotiations with the Monterey Bay National Marine Sanctuary began immediately, and permission was granted to push a few of the larger rocks down to the ocean. Negotiations were started to determine a permanent disposal site for the rest of the material. In the interim, material is being hauled to highway turnouts for temporary storage. The only designated permanent disposal site to the north is at Garrapata Creek nearly 40 miles away, and at Willow springs 20 miles south. There are very strong reasons for not hauling this material (an estimated 20,000 cubic yards = about 2000 truckloads) such a long distance, including expense, pollution, noise, road kill, public safety, and degradation of the highway itself. Thus the question of disposal of the material is critical.

The land on which the slide occurred is part of the University of California Landels-Hill Big Creek Reserve, an area owned by the University and dedicated to protecting and studying natural processes. The ocean waters below the slide are part of the Big Creek Marine Ecological Reserve, an area of ocean set aside for the scientific study of marine resources and also dedicated to the study of natural processes. These two entities may be lumped together as the "Big Creek Reserve." The ocean waters are also part of the Monterey Bay National Marine Sanctuary, an area dedicated to protection of natural resources. The mission of all these entities includes protection of natural processes against human disturbance. If the Big Creek slide were a natural event, contributing rocks and fine material to the shoreline below, it would be considered an opportunity for scientific study of the effects of landslides on ocean habitats. studying, to see effects on ocean habitats below

It is therefore important to determine the degree to which landslides represent a natural process which feed natural habitats downslope and contibute to existing natural communities.

Suggested Guidelines

1. Natural occurring slides should be encouraged to flow unimpeded to the habitats below. If material from such a slide is caught by the highway it should be pushed over the edge (using appropriate equipment and techniques).

2. Debris and material generated by planned construction projects, including large scale highway stabilization projects, should be deposited in an appropriate, pre-planned receiver site. Since these seem to be lacking along most of the Big Sur coast it follows that large scale earthmoving is usually not appropriate, either.

3. Material from slides which originate from previous highway construction and/or current maintenance should be treated on a case by case basis. In some cases the material can be added to a pre-existing slide, or placed where a natural slide seems imminant. This strategy seems appropriate for the Big Creek slide, since it is in the center of a naturally occurring slide deposit.

4. It is desirable to know if any particularly valuable or rare natural resources are in the path of slide disposal sites. This information can be difficult to obtain in marine environments, but an attempt should be made if feasible. Ideally, a shoreline survey, looking for unusual species, should be conducted under all potential landslide sites. C.A. Hall's geological map could be used to determine the location of present and past landslide events.

5. Given the strong mandate for natural area protection within the Big Creek Reserve, it is not appropriate to bring outside material into the reserve for disposal.

6. Any earth moving involves the potential for dispersal and propagation of undesirable plants. In general, plants from other areas, native or not, should not be brought in to the reserve. Revegetation with on-site native plants is preferred. This can often be accomplished by carefully protecting topsoil and vegetative rootmasses and stems, and spreading them over disturbed areas. Follow-up weeding of undesirables may be necessary. This procedure worked well for revegetation of the Wing Gulch access road (disturbed in May 1998), which now has a high percent cover of on-site native plants.

The Big Creek Slide of March 2000 This slide is an example of a natural process, the timing, scale, and dynamics of which have been altered by highway construction and maintenance. Given the absence of alternative disposal sites, and unless a unique natural resource would be obliterated, we recommend that the material be pushed into the ocean below the slide. An alternative would be to deposit some or all of the material on land adjacent to the slide, below the naturally occurring slip faces above. The exact placement should be such that impacts to natural habitats are minimized (in this case the stands of willow should be protected, and topsoil should be set aside for spreading over the fill.) We should not allow material from distant slides outside the reserve to deposited, since this would compromise the scientific/educational value and pristine natural condition of the reserve.

Below are photos of the slide (from both ends) and of the ocean below the slide. At bottom are two photos of a proposed receiver site for some or all of the slide material. Photos taken March 13 and March 16, 2000

   

 View of slide from north 3-13-00

 Marine reserve habitats below slide 3-13-00
   

 View of slide from south 3-14-00

 View of Bull Kelp (Nereocystis) beds below slide 3-14-00
   

 Disposal site marked in white; note that willow habitats are avoided. 3-16-00

 New beach sand deposited after recent creek flooding. 3-15-00

By March 18, CalTrans had not secured permission from the Monterey Bay National Marine Sanctuary to push the slide material over the side. They began preparing the alternate disposal site shown in the photos, land which is partly in the State Highway right of way and partly on Big Creek Reserve lands. Under the direction of the Big Creek manager John Smiley, CalTrans flagged out an area covered by old slide material, Poison Oak (Toxicodendron diversilobum), California Sagebrush (Artemisia californica), Clematis sp., Coyote Bush (Baccharis pilularis), Mugwort (Artemisia douglasiana), and Hemlock (Conium maculatum). Vegetation and topsoil were removed using an excavator. Several large clumps and root masses of Clematis vine were removed intact, along with a few Coyote Bush and Sagebrush plants. Then, the remaining vegetation and topsoil were gathered into a central pile and removed to a safe location. By late afternoon, trucks were unloading slide material into the cleared area. CalTrans hopes to fit all the slide material into the one site within about 7-10 days. After the site is smoothed off, the topsoil and plants will be replaced and tamped down. Some watering may be necessary to bind the material together if it doesn't rain.

 

   

 Excavator gathering vegetation and topsoil 3-18-00

 Loader picking up vegetation and soil for storage. 3-18-00
   

 Slide material being pushed over site 3-20-00

 Native plant recovery Wing Gulch access road after 2 years (see lower part of photo, right of center, non-native Pampas Grass is off the road but should be removed!)

During the following week, the majority of the material from the Big Creek slide was deposited onto the fill site. The depression around the culvert was filled in, and the level of the ground raised 10-20 feet in the center. Once all the filling had taken place, the topsoil and vegetation was moved back to the base of the fill site. On March 30, John Smiley assisted the excavator operator in replacing the topsoil. Because the amount was limited, the soil was placed in 10' diameter patches about 12" deep. The result can be seen in the photos below.

 

 View below slide showing slide material on beach 4-30-00
   

 Preparing to replace topsoil 3-30-00

 Making soil patches 3-30-00
   

 Carryong topsoil across the slope 3-30-00

 Closeup of soil patch after being watered 4-1-00
   

Completed soil patches 

 Slide area from northwest 4-1-00

 

 

 Seedlings germinating in soil patches 4-10-00

 Seedlings germinating in soil patches 4-10-00

By May 11, 2000 there was a thin layer of greenery on the soil patches. The seedlings photographed above were seen to be hemlock, mustard, and thistle, all exotic weeds. No seedlings were found on the sterile ground between patches. The unseasonable germination is expected for weed species which are not tuned to the California cycle of summer drought. We will keep a close watch and chop these weeds before they can reproduce. John photographed a 60 year old road cut just north of the Big Creek bridge to document the slow rate of succession on sterile rocky east-facing slopes.

   

 Mustard (Brassica sp.) seedlings on lower soil patches which were watered on
 Milk thistle (Silybum marianum) and hemlock (Conium maculatum) seedlings on lower soil patches.
   

 60-year-old road cut, facing east, just north of Big Creek Bridge, colonized by Dudleya and Stephanomeria plants 20-40 cm across.

 Hemlock seedlings on upper soil patches, germinated after late-April rains.

   
 By July, the regrowth was extensive on the soil patches. In early July we scattered seeds of California Poppy (Eschscholzia californica) over the soil patches.  Much of the regrowth was by non-native mustard (Brassica sp) but native lupines (Lupinus sp.) were growing well. We plan to scatter seeds over the bare areas in the near future.

In late July, 2000, we scattered about a pint of Bush Lupine seeds (Lupinus arboreus) across the site, both on and off the soil patches. We also scattered a few ounces of California Poppy seeds (Eschscholzia californica) over the same areas. We also spread seed under the Big Creek bridge on the site of the bridge retrofit project.

   

 This photo shows the slide material deposit (upper left) and an adjacent natural slide face (lower right). Note the similarity of appearance. 10-3-00

 By December we had some good rain (in October) and lots of seeds sprouted. There are quite a few California sagebrush plants (Artemesia californica) as well a regrowth of mustard (Brassica sp.) and some hemlock (Conium maculatum) seedlings. 12-5-00
   

 Perhaps the most common sprouter is the hedge nettle or wood mint (Stachys bullata) 12-5-00

 There are even some nightshade plants (Solanum douglasii). As of this date I did not see any sprouts of Yellow Bush Lupine or the California Poppy. 12-5-00

As of 1-14-01 plant growth was vigorous on the soil patches, with very little growth in between. Most of the growth was hedge nettle (Stachys bullata) and California Sagebrush (Artemisia californica). We removed a few large milk thistle plants (Silybum marianum) and one star thistle plant (Centaurea sp.), growing on the sterile fill between soil patches. Hemlock (Conium maculatum) is the most common weed on the soil patches, but some herbivore is defoliating it (see photo). It looks like a caterpillar is doing the work!

   

 Soil patches greening up, primarily with native plants (Stachys bullata, Artemisia californica) 1-14-01

 Hemlock (Conium maculatum) plant, defoliated by some herbivore, perhaps a caterpillar. 1-14-01
   

 Hedge nettle (Stachys bullata) and California Sagebrush (Artemisia californica) growing vigorously on the soil patches. 1-14-01

 Star thistle plant (Centaurea sp.), growing on the sterile fill between soil patches. 1-14-01
   

 By April, 2001 vegetation has grown considerably. Here a grass has seeded into the rocky slope between soil patches. 4-24-01

 A closeup of the same grass. Should this plant be allowed to propagate? Decisions like this are part of the challenge involved in revegetation projects. 4-24-01
   

 The soil patches are now well-vegetated. Hedge nettle is still dominant, along with California Sagebrush and mustard, but there are thistles and hemlock which we are removing as soon as we spot them. 4-24-01

 We are trying to prevent the mustard from setting seed. There is a lot of bur-clover coming in right now (behind the machete), but this fragile plant will set seed and die soon. 4-24-01

As of 9-18-01, most vegetation on the soil patches had dried out, except for a few species: hedge nettle, mugwort, California sagebrush, and bush lupine. The grass which invaded the receiver site bare patches has also dried out, and is clearly the same species that grows on the slopes above.

   

Many paths cross the area, made by stone masons collecting building rock. 9-18-01
 California Sagebrush (Artemisia californica) is fairly dry but definitely alive on the slopes. 9-18-01
   

 Mugwort (Artemisia douglasiana) is also doing well. 9-18-01

 Dock (Rumex sp.) has recently begun to take hold in the soil patches. 9-18-01
   

 The grass (reported above, in spring) has grown and dried on the bare zone. It is very common on the natural slide faces above. 9-18-01

 Here is a closeup of the grass fruiting stalks. 9-18-01
   

 Here is a view of the receiver site showing the soil patches as viewed from a hill to the northwest. The dry grass is visible on the slopes above. 9-18-01

 This is a comparable view of the disturbance zone under the bridge, where soil patches were not saved. With our "20-20" hindsight, we should have scraped off the topsoil and saved it for later deposition 9-18-01

The rains came in December and soaked the slopes, creating excellent conditions for seedling germination. By early January 2002 millions of tiny clover plants had genminated in the soil patches, covering the ground between the perennial species. The material between soil patches also showed signs of revegetating, albeing with annual grasses. Relatively few thistle seedlings were seen.

   

 The soil patches are covered with a species of clover (Trifolium sp). 1-8-02

 In addition to the clover, the Hedge Nettle (Stachys bullata) and other perennials are growing well. 1-8-02
   Between soil patches on the "sterile" material, a slight vegetative cover is forming from the annual grass growing on the slopes above and a small annual grass species. 1-8-02

See continuing photos and commentary of the site restoration after June 2002.

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