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SAN CLEMENTE ISLAND ATV TRAIL SYSTEM- INSTALLATION OF EROSION CONTROL

DEMONSTRATIONS

INTRODUCTION

The San Clemente Island ATV trail system was established during 2000 in support of the Institute for Wildlife Studies’ San Clemente loggerhead shrike release and predator control programs. The trail system was inspected during December 2000 by Soil Ecology and Restoration Group (SERG) employee John Ekhoff, and surveyed for erosion control needs. Trail sites were prioritized according to associated risk such as present gullies, sink holes and slope stability. Following this survey, a list of project goals was established, including: 1) signing and blocking closed areas, 2) implementing erosion control in high risk areas with simple rock water bars and diversions, 3) testing installations of water bars, armoring, soil glue, porous pavement and rolling dips to establish compatibility with ATVs, 4) mapping trails from recent air photos and establishing monitoring points to determine rate of erosion and gully formation, and 5) reviewing special risks for archeological sites and developing erosion control strategies and barriers as appropriate.

During 14 and 15 November 2001, SERG project managers Amy Rusev and Jonathan Dunn surveyed approximately the first mile of three ATV trails on the west side of San Clemente Island. Recommended erosion control demonstrations were tentatively assigned to the individual trails. The installation of the demonstrations was planned for completion during the month of December 2001.

Over12-14 December 2001, Amy Rusev, with SERG employees Thomas Jodoin and Jimmy Machado, implemented various erosion control demonstrations within the San Clemente Island ATV trail system according to project goal number three cited above. The five types of erosion control methods represented are: wood trail drain, rubber water bar, rock water bar, rolling dip, and Soil Sement. These demonstrations were installed near the ATV trailheads to facilitate accessibility for site visits and monitoring. Six demonstrations (one demonstration/method plus an additional rock water bar) were completed in total among the following three ATV trails: Tombstone, Norton Canyon, and Horse Canyon (Figure 1).

Soil Ecology and Research Group

last update December 8, 2002

of 11San Clemente Island Erosion Control

3/23/2005http://www.serg.sdsu.edu/SERG/restorationproj/channel_islands/erosion/project%20report.html

Figure 1. Location of erosion test sites.

The San Clemente Island demonstration site locations were chosen in moderately sloped and degraded areas near the trailheads in order to ensure that future site visits would require little effort. In addition, all equipment and materials were walked to site locations from a parked vehicle at the road/trail interface. The cost analysis for the various erosion



control types does not account for the difficulty in transporting equipment and materials to remote trail sites if large-scale remediation efforts are warranted. MATERIALS AND METHODS

Materials

The installations that required pre-construction before being transported to San Clemente Island by barge were completed at San Diego State University on 22 November 2001. These included the rubber water bar and the wood trail drain. The materials required for construction included: 2”x4”x8’s, 2”x6”x8’s, 2”x8”x8’s, bolts, nuts, washers, wood screws, and a 12 foot length of conveyor belt. David Bainbridge supplied all installation construction designs.

A 5-gallon drum of concentrated Soil Sement and a 3-gallon hand pump spray applicator were purchased for the Soil Sement trial.

Tools used for the erosion control installations included: Hilti TE 55 Powerhammer, Honda 1000 generator, trench shovel, digging shovel, rock bar, digging bar, and pick axe.

Methods

Installation of the wood trail drain, rubber water bar and rock water bars required digging a trench approximately perpendicular to and intersecting the ATV trail. The trenches were six to ten inches in depth and constructed at a slight angle, so that the draining end worked with the natural topography of the surrounding area. The various erosion control devices were then fitted into the trenches and tamped in using rock bars. Finally, the discharge point of the erosion control devices was armored with small to medium-sized rocks from the surrounding area to diffuse draining water and prevent gullying (Figures 2 through 7).

Figure 2. Wood trail drain installation on Tombstone Trail.



Figure 3. Wood trail drain installation and armoring complete on Tombstone Trail.

Figure 4. Site for rubber bar installation for Tombstone Trail.



Figure 5. Rubber water bar installation and armoring complete on Tombstone Trail.

Figure 6. Trench for rock water bar installation on Tombstone Trail.



Figure 7. Rock water bar installed on Tombstone Trail.

The rolling dip was constructed so that the gradual “dip” and “roll” would barely be noticed by an ATV rider. A volume of soil was dug and removed from the up-slope section of the trail and spread out over the contiguous down-slope section. The lowest depth of the “dip” was approximately six inches below the soil surface of the existing grade and the height of the “roll” was approximately 6 inches above the surface of the existing grade. The rolling dip was constructed over a 10-foot section of trail. This method allows draining water to collect in the “dip” and flow off the trail. The discharge point was armored with small to medium-sized rocks from the surrounding area to diffuse draining water and prevent gullying (Figures 8 & 9).

According to the product’s guidelines, the concentrated Soil Sement product requires dilution at a ratio of nine parts water to one part Soil Sement and no more than ten gallons of the diluted Soil Sement should be applied per 40 ft2. The diluted product was placed in a 3-gallon hand pump spray applicator. Our plan was to apply between 6 and 9 gallons of the diluted product over 40 ft2. Our spray applicator, however, was not effective for applying the Soil Sement. The product dried quickly and obstructed the spray nozzle in our low-pressure applicator. While a total of 4.5 gallons diluted Soil Sement was applied over a 40 ft2 section of trail (Figure 10), this amount may be insufficient for testing purposes. A high-pressure applicator would be necessary for application of this product on a larger scale.

RESULTS

The following lists contain data collected in the field at San Clemente Island. A simple data sheet was designed prior to commencement of the fieldwork and was filled out completely during each erosion control installation.

Wood Trail Drain

Date: 13 December 2001 Location: Tombstone Trail UTM coordinates: N-3638010, E-0362313 Number of Personnel: 3 Equipment/Materials: Hilti TE 55 hammerdrill, Honda 1000 generator, shovels, rock bars, pick Total cost of raw materials: $14.59



Labor time for assembly: 45 minutes Labor time for installation: 105 minutes

Figure 8. Site for rolling dip installation on Norton Canyon Trail.

Figure 9. Rolling dip completed on Norton Canyon Trail.



Figure 10. Soil Sement site following application on Horse Canyon Trail.

Rubber Water Bar

Date: 12 December 2001 Location: Tombstone Trail UTM coordinates: N-36343311, E-0483463 Number of Personnel: 3 Equipment/Materials: Hilti TE powerdrill, Honda 1000 generator, shovels, rock bars, pick Total cost of raw materials: $7.10 + conveyor belt (price variable) Labor time for assembly: 30 minutes Labor time for installation: 75 minutes

Rock Water Bar

Date: 13 December 2001 Location: Horse Canyon Trail UTM coordinates: N-3638061, E-0362313 Number of Personnel: 3 Equipment/Materials: Hilti TE powerdrill, Honda 1000 generator, shovels, rock bars, pick Total cost of raw materials: N/A Labor time for assembly: N/A Labor time for installation: 75 minutes

Date: 12 December 2001 Location: Tombstone Trail UTM coordinates: N-36343311, E-0483463 Number of Personnel: 3 Equipment/Materials: Hilti TE powerdrill, Honda 1000 generator, shovels, rock bars, pick Total cost of raw materials: N/A Labor time for assembly: N/A Labor time for installation: 75 minutes

Rolling Dip



Date: 13 December 2001 Location: Norton Canyon Trail UTM coordinates: no data collected Number of Personnel: 3 Equipment/Materials: Hilti TE 55 hammerdrill, Honda 1000 generator, shovels, rock bars, pick Total cost of raw materials: N/A Labor time for assembly: N/A Labor time for installation: 60 minutes

Soil Sement

13 December 2001 Location: Horse Canyon Trail UTM coordinates: N-36343311, E-0362174 Number of Personnel: 2 Equipment/Materials: 1 Gallon Soil Sement, pump spray applicator, 10 Gallons water Total cost of raw materials: $45.00 Labor time for assembly: N/A Labor time for installation: 30 minutes

Summary Table

The values in Table 1 reflect the various erosion control treatment total installation costs (personnel salary at $15.00/hour).

Table 1. Comparison of Erosion Control Types

DISCUSSION

In comparing the five types of erosion control methods, three major areas must be analyzed: method cost (materials), method installation (time), and method efficacy. The method cost and installation time were comparable for the various demonstrations, with the exception of the wood trail drain, which was almost twice the cost of the other methods and may degrade more quickly over time. The rubber water bar and rock water bars were the easiest to install. The availability of good rocks for the rock water bar was not an issue in our work areas; however, the fact that the rocks do require locating and transporting to the site may present a problem in some areas of the ATV trail system. The availability of conveyor belt or similar material for the construction of rubber water bars could also be a limiting factor if this method is to be applied on a larger scale. The rolling dip was the least expensive to install. The Soil Sement

Erosion Control Type

Analysis Wood Trail Drain Rubber Water Bar Rock Water Bar Rolling Dip Soil Sement

Material Cost $14.49 $7.10 N/A N/A $45.00

Time for Pre-construction 45 min. 30 min. N/A N/A N/A

Total Time for Installation 105 min. 45 min. 75 min. 60 min. 30 min.

Total Cost $112.25 $63.35 $56.25 $45.00 $67.50



product was not applied in sufficient quantity due to applicator failure. The expense in purchasing a high-pressure applicator for demonstration purposes was not feasible for experimental purposes.

For analysis purposes, the cost of repairing eroded areas and inhibiting future erosion on sloped sections of the San Clemente Island ATV trail system are presented for three trail lengths (based on a trail width of 1.5 meters): 100, 250 and 500 meters. Because the total length of severely damaged trail has not yet been assessed, we will present the cost analysis results in this way so that they may be applied at a larger scale once total trail damage has been accurately analyzed. The majority of the trail length falls within a slope gradient between 10 and 35 degrees. Taking 18.75 degrees to be the average gradient, erosion control of the method types examined would need to be installed at 5 meter intervals, on average. This distance was based on our experience with trail erosion control activities with the United States Forest Service and the Off-Highway Vehicle Division of the California State Parks Department. Table 2 contains cost analysis data based upon our results from the installation of erosion control demonstrations.

Table 2. Erosion Control Cost-Analysis

* These values may not represent the true costs of applying the Soil Sement product (the cost of renting or buying a pressurized sprayer was estimated)

The efficacy of each erosion control type will need to be analyzed following the wet winter months of 2002-2003. Monitoring devices were installed at the base of some trail slopes and within gullies during the month of January 2002. Metal erosion control pins were buried at a depth of six inches leaving an exposed six inches above the soil surface. Siltation and gully formation can be monitored by recording the length of the exposed pins following precipitation events over time. Rates of change in road surfaces will be monitored using a string gauge. Two surveyor chaining pins will be installed so that they straddle each ATV trail. Following a precipitation event, a string is run between the chaining pins and perpendicular measurements (from the string to the soil surface) are recorded along predetermined horizontal intervals across the string. Using these methods, we will record loss of topsoil from the surface of sloped trail sections and the rate of gully formation. Monitoring devices can be installed within the trails near the erosion control demonstrations and within additional sections of the ATV trail system for comparison. From these results, we will be able to track the efficacy of the various erosion control types.

While the installation of the erosion control demonstrations was relatively easy, several realities need to be seriously considered. We worked close to trailheads where the erosion damage was minimal relative to more remote trail sections. In addition, transportation of equipment and materials to distant sites could be extremely costly. While it would be more cost effective to bring heavy equipment onto the trail system for large-scale erosion control installations, this is not a feasible option from a natural resource perspective. The widening of the trails from equipment

Total Cost

Erosion Control Type 100 meters 250 meters 500 meters

Wood Trail Drain $2,245.00 $5,612.50 $11,225.00

Rubber Water Bar $1,267.00 $3,167.50 $6,335.00

Rock Water Bar $1,125.00 $2,812.50 $5,625.00

Rolling Dip $900.00 $2,250.00 $4,500.00

Soil Sement* $1,050.00 $2,625.00 $5,250.00



transportation and heavy compaction make this option counterproductive. Therefore, material and equipment would need to be transported on foot or using ATVs.

RECOMMENDATIONS

Professional consultation in the area of erosion control is recommended in the near future for the SCI ATV trail system. A professional OHV trail designer from a federal agency such as the United States Forest Service will be contracted by SERG personnel during the month of January or early February for a one-day San Clemente Island site visit. On this day, the OHV trails will be examined and comments and recommendations will be documented. Erosion issues threaten natural resources as well as the safety of the ATV riders. The need to evaluate all aspects of the existing problems as well as prevent against future crises is imminent.

Additionally, we recommend that the U.S. Navy consider conducting more quantitative testing of the various erosion control methods. The Soil Erosion Laboratory at San Diego State University has the capabilities of manipulating precipitation events, slope angle and other variables in the confines of its laboratory, thus providing quantitative data with which to compare the efficacy of the various methods installed on San Clemente Island.



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