A CS2 erosion control mat was installed during the St. Thomas ESC training workshop to demonstrate the use of ESC mats for channel stabilization, proper installation techniques for the practice, and to evaluate its effectiveness in promoting grass seed germination, as well as its durability. The mat was installed in the overflow swale from a sediment retention pond.  

The mats installed at all sites have biodegraded significantly. The straw/coconut fiber (CS2) mat has been the most durable, taking approximately 6 months to disintegrate, whereas the excelsior mat installed on St. Croix completely disintegrated after only 2 ½ months; this may be partially due to the high rainfall that occurred during June and July 1998.

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TASK 3: STRUCTURAL PRACTICES

Silt Fencing

Silt fencing was also was installed at the CES - St. Thomas Home Demonstration Garden in March 1999 to prevent soil on the slope above the driveway from eroding and silting in the driveway. Signs describing the project and comparing good and bad silt fence installation practices were produced and the fence is being maintained as a demonstration of proper installation. The fence is functioning properly in keeping sediment from flowing off the slope onto the driveway.  

Triangular Dikes

A triangular dike was also installed during the St. Croix ESC training workshop to demonstrate how it can be used as a check dam in a swale leading to a drainage culvert. Participants cleared the area for the dike, anchored it in, and backfilled soil and rock on top of dike flaps to hold it in place. During a follow-up site visit on June 29, 1998, the triangular dike was found to be functioning properly, with approximately one inch of sediment observed accumulated behind the dike. Triangular dikes were also used on the St. Thomas CES parking lot during excavation and grass germination to prevent soil from washing off the driveway and into the road (see below).  

Porous Paving

• Control erosion and flooding problems experienced at the site;
• To demonstrate the use of porous paving systems, as compared to gravel or bare soil, to reduce stormwater runoff and erosion; and
• To evaluate the materials' durability under VI conditions.

CES staff prepared the CES Home Demonstration Garden (removed weeds, cut back invasive bush, dug out and removed diseased trees) prior to the demonstration. Staff worked with a UVI architect to map out the St. Thomas CES office driveway and parking lot demonstration sites. The parking lot and driveway were then excavated and graded for the demonstration; the lot was also rolled with a vibrating roller to smooth it.

Installation occurred in early February 1999 by CES staff with assistance from crew and the product's distributor in Puerto Rico. The web installation in the driveway was conducted as part of a hands-on workshop for thirty-seven (37) attendees. Participants were shown a video describing the use and proper installation of the material, and then participated in installing the webbing. Each 20' long section of the GeoWeb® was stretched and anchored (using j-bars along the sides and end pieces) down the driveway, and the sections were joined with staples. The webs were then filled (by backhoe) with crushed stone and soil, and the stone and soil was rolled with a vibrating roller to enhance compaction.

CES staff installed the GeoBlocks® in the parking lot the following week. The blocks were laid flat and interlocked, with the edges anchored using j-bars. Uneven edges were cut using a saw to provide more level coverage. A backhoe was used to filled the blocks with topsoil, the soil was raked level by hand, and stones were removed. The parking lot was then seeded with a mix of bermuda, rye and bahia grasses and covered with straw erosion control mats to hold in moisture and prevent birds from eating the grass seed.

The parking lot was watered and fertilized to promote faster grass germination and establishment. Parking was prohibited on the lot for three (3) months so that the grass could become well established. Heavy use of the drive portion of the lot has damaged some of the grass, but the grass in the parking areas along the side is holding up well.

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TASK 4: PUBLIC OUTREACH

• A project report was presented detailing the completed portion of the first phase of the project (vegetation and erosion control matting stabilization demonstrations) at the 1997 V.I. Nonpoint Source Pollution Conference.
• Practice installation demonstrations were carried out at the 1997 NPS Conference (50 attendees), the January 1998 St. Croix Hydroseeding Certification Workshop (30 attendees), the Practical Approaches for Effective Erosion & Sediment Control training workshops held May 28 - 29 and June 2 - 3, 1998 on St. Thomas and St. Croix (34 attendees), and the Porous Paving demonstration held February 5, 1999 (37 attendees). Participants included architects, engineers, draftsmen, contractors and regulators (see above).
• Articles on the project, highlighting the Donoe Housing Community erosion control mat demonstration and the installations performed during the Practical Approaches for Erosion & Sediment Control Workshop, appeared in the V.I. NPS Update Spring and Summer 1998 Newsletters, which were distributed to 1100 architects, businesses, contractors, draftsmen, engineers, policy-makers, regulators, and other interested members of the general public.
• This web page linked to the UVI-CES home page was developed and uploaded on the UVI-CES website outlining the objectives and accomplishments of the project http://rps.uvi.edu/CES/ESCdemo.htm.
• Photographic and video records have been kept of the various stages of the project and project activities for use at DPNR/VICD/VICES workshops and conferences.
• Signs designating the demonstration project were installed at the Donoe Housing Community demonstration site, the CES Home Demonstration Garden, and the CES St. Thomas driveway/parking lot demonstration.
• An erosion control model was built for use at the CES Home Demonstration Garden for workshops and tours and at fairs and conferences.
• A presentation entitled "Promoting Erosion & Sediment Control in the U.S. Virgin Islands" was delivered at both the International Erosion Control Association's Conference and Trade Show held February 21-26, 1999 in Nashville, Tennessee (the paper was also published in the conference proceedings) and at the USDA-NRCS Caribbean Area district conservationist's annual meeting, held July 20 - 22, Dorado, PR.
• A brochure, targeted to the general public, was developed outlining the goals and highlights of the project demonstrations (various practices installed and results observed).
• The project was advertised through radio shows and public service announcements.
• Tours of project sites will continue to be conducted for government personnel, architects, engineers, developers, contractors and the general public.
• A 60-second public service announcement for television, utilizing film footage taken during demonstration installations, and new radio PSAs is being developed.

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CONCLUSIONS

Vegetation

Vetiver is easily propagated from cuttings. The first method of propagation involved removing sections from a parent plant (root and leaf material), trimming excess roots (leaving only 3") and (leaving 4" of leaf). "Plugs" were then planted directly in the demonstration plot and watered daily. This first planting took 4-5 weeks to develop new shoots. However, we discovered a faster, more reliable method of propagation: materials were prepared as before but then rooted in water for about 4 days (until new root material was observed). The plugs were then transplanted into the demonstration plots. This second planting took 2 weeks to develop new shoots. Using this method of propagation, no mortality occurred, whereas the previous method resulted in approximately 20% plant mortality.

Hydroseeding can be a very effective erosion control practice, but only if sufficient moisture is available for grass germination and propagation. This means that bare soils should be seeded either during the rainy season or else supplemental water must be provided to ensure success. Success rates increase in areas where shade is present, particularly on north-facing slopes, and if a mulch is provided.

Erosion Control Matting

Straw mats (100%) are specified for use on 2:1 (25%) slopes up to 75' in length, but were observed to prevent erosion on shorter slopes up to 1:1 (50%) steepness. Straw (70%)/coconut (30%) fiber mats are specified for use on 1:1 slopes up to 75' in length, and were observed to perform well on even steeper slopes (~60%) that were shorter in length (no greater than 50'). Excelsior fiber mats were not sufficiently durable under demonstration conditions.

Silt Fences

Triangular Dikes

Porous Paving Systems

Grassed block/grid cellular confinement systems can work well in controlling erosion and stormwater on fairly level, low-use traffic areas, such as emergency access areas, driveways or parking lots. For higher or heavier used parking areas, gravel fill would be more appropriate, as continual vehicular traffic damages the grass base. Some disadvantages for use in the V.I. have been observed on the grassed demonstration system. First, the subsurface must be completely level for the blocks to lay properly. Secondly, for a grassed parking area that requires soil fill, the blocks should be filled by hand in order to avoid over-filling with soil. Over-filling reduces the blocks ability to protect grasses planted within the system so that continual traffic will damage the sod.