Soil Ecology and Research Group last update July 21, 2003

DRAFT IMPLEMENTATION REPORT FOR
FISH POND EROSION CONTROL AND REVEGETATION SITE
ON MARINE CORPS AIR STATION MIRAMAR
SAN DIEGO, CALIFORNIA

 

Executive Summary
The Marine Corps Air Station, Miramar Fish Pond is under restoration for recreational use by Station personnel as well as to ensure long-term viability of the pond. Three sites adjacent to the pond were identified by station personnel as having experienced severe erosion and in need of both corrective and preventative measures. To mitigate this situation, the Soil Ecology and Restoration Group of San Diego State University was contracted to install biodegradable erosion control measures along with the planting of native seedlings. Work on the three sites occurred between October 2002 and April 2003.

Site 1 was an erosion gully approximately 20 feet wide, slightly over 100 feet long, and up to 6 feet deep in the center. This was filled in with soil from the top lens of the gully and compacted for stabilization. Jute netting was used to provide initial biodegradable erosion control and forty native seedlings were planted at this site.

Site 2 is located in the arc of the Fish Pond access road and the pond’s north shore road intersection and is approximately 9,000 square feet in size. To reduce sheet runoff, the slope was re-contoured in the same manner as Site 1 and surface preventative measures, including the use of straw flake dams along with machine and hand pitting were implemented to minimize any remaining sheet flow runoff. Eighty native seedlings were planted at this site.

Site 3, located on the slope near the southwest corner of the dam, is approximately 34,000 square feet in size and consisted of a large eroded slope with a steep headwall along the top edge. Corrective action consisted of filling in the eroded areas using the soil located on top of the mesa in the same manner as done for Site 1. The headwall was removed and the slope recontoured. The use of jute netting, straw flake dams, and hand and machine pitting of the slope was done to help minimize future erosion activity. Straw bale dams were also installed along the top edge of the slope to prohibit sheet flow runoff. Approximately 200 native seedlings were planted at the site.

All planting was done during the rainy season to help ensure plant survival, and seedlings were supplied with plant protection devices. Irrigation was conducted every two weeks during the hot summer months, using a temporary gravity feed irrigation system for Sites 1 and 3 and hand watering into deep pipes or basins for Site 2. Weed removal was done as needed by both hand and mechanical methods and the application of herbicide by a licensed professional.

At the end of one year, growth analysis was conducted to measure the increase in plant volume. Site 3 had the greatest increase in plant volume, while the species Mimulus aurantiacus had the largest increase in plant volume of all species planted over the one-year period. Percent survival was also taken for each site. Each site met the required 75% survival at the end of the one year period, with Site 1 at 77%, Site 2 at 92% and Site 3 at 100%.

Introduction
Marine Corps Air Station Miramar, or the “Station”, is required to manage its lands to control and prevent soil erosion and conserve natural resources. Erosion control preserves soil quality and supports re-establishment of vegetation. Excess sediment or altered water flows can affect watershed hydrology function, water quality, and fish and wildlife habitat. Excess runoff due to watershed malfunction can lead to the degradation or destruction of entire ecosystems, individual plant communities, or specialized zones such as riparian areas along stream banks. Gullies can also potentially affect the vegetation and hydrology of the watershed by lowering the water table (Integrated Natural Resources Management Plan. Dames and Moore, May 2000).

The Miramar Fish Pond is under restoration for recreational use by Station personnel. The restoration will ensure the safety of the personnel using the Fish Pond as well as prevent further erosion and damage to the surrounding soil, habitat and the pond itself. Three areas were identified as being in need of erosion control around the Fish Pond. Work was done in these three areas to stabilize the soil, reduce runoff, and revegetate the areas.

Background
The basic causes of erosion at all three sites appear to be historical in nature, probably dating back to when the pond and the surrounding roads were first constructed. Slopes were left at too steep an angle, which allowed water to be channeled onto the slopes and subsequently led to heavy erosion. Fortunately, none of the slopes were very large and problems could be readily corrected by the installation of preventative measures to ensure future erosion is minimized.

Project Location and Site Description
The Station is located in San Diego County on the southwest coast of California. It is four miles inland from the Pacific Ocean, and thirteen miles north of downtown San Diego. The Station is located within the incorporated area of the City of San Diego. Main access to the Station is by Miramar Road and Interstate 15. State Route 52 bounds the southern end of the Station while Interstate 805 forms the western boundary. The Fish Pond is located on the Main Station of MCAS Miramar. Three distinct areas around the Fish Pond were identified by station personnel as needing erosion control measures; Site 1, Site 2, and Site 3.

Site 1 is approximately 4,000 square feet in size and is located on the north side of the pond. It stretches from the ridge above the pond down to the road which runs along the north shore of the pond. The initial condition of the site was an erosion gully approximately 20 feet wide, slightly over 100 feet long, and up to 6 feet deep in the center, apparently caused by run-off from the compacted bare area located adjacent to the Fish Pond access road. Two large piles of dead brush that had been placed at the top of the gully. Figures 2 through 4 show how Site 1 initially appeared.

Site 2 is located at the northeast corner of the Fish Pond dam where the access road intersects with the pond’s north shore road and appears to be approximately 9,000 square feet in size. The site initially had been seriously affected by sheet runoff originating from the fairly steep access road. Figures 5 and 6 show Site 2 prior to restoration efforts beginning.

Site 3 is located on the slope near the southwest corner of the dam and was the largest and most extensively damaged area. It is approximately 34,000 square feet in size and initially consisted of a large eroded slope with a steep headwall along the top edge, probably created during the construction of the dam and the adjacent access road. The headwall had several areas where rockslides recently occurred and thus posed a safety hazard for personnel using the Fish Pond. The site had apparently suffered sheet runoff from the large bare area located above the slope that had been used for storage of excess fill dirt. Figures 7 through 10 show Site 3 as it initially appeared and the degree of erosion present on the site.

Site 1 Before Work.

Figure 2. Site 1 before work from the opposite side of the fish pond.

Figure 3. Top of Site 1 before work.

Figure 4. Site 1 before work from the bottom of the site looking up.

Site 2 Before Work.

Figure 5. Site 2 before work from the opposite side of the pond.

Figure 6. Main portion of Site 2 before work.

Site 3 Before Work.

Figure 7. Site 3 before work from across the fish pond.

Figure 8. Site 3 from below before work.

Figure 9. Erosion on Site 3 before work.

Figure 10. Erosion on Site 3 before work.

Methods and Materials

Site 1.
The two large piles of dead brush at the top of the gully were removed and the gully filled with soil from the top lens of the gully. The work was done with the use of a D-4 bulldozer and completed in several layers. Each layer was approximately 1-2 feet in depth and was filled in, moistened with water, and then cat-walked to stabilize it before the next layer was added. Use of the soil from the top lens ensured that the physical and chemical makeup of the soil most closely resembled the properties of the adjacent native, undisturbed soil. The use of native soils provides a more suitable environment for growth and development of native seedlings used for cover and prevention of future erosion problems. Soil recovered from the Fish Pond was not used due to its different chemical and physical makeup.

Once the gully was filled in and compacted, jute netting was installed to provide initial biodegradable erosion control (Figures 11 and 12). After jute netting installation was complete, forty (40) native seedlings, outlined in Table 1 (page 17) and grown in the SERG shade house, were transplanted onto the slope. Forty seedlings provide the necessary cover for the site, which is slightly less than one-tenth of an acre (Figure 13). Planting occurred during the rainy season to help ensure survival. Plants were supplied with plant protection devices (treepees or tubex) to allow protection from herbivores and the elements. Weed mats were placed around the base of each plant to reduce weed growth and competition in the area water was delivered to the plant.

Site 1 Preparation and Planting.

Figure 11. Installation of jute netting on Site 1.

Figure 12. Jute netting on Site 1 after installation. .

Figure 13. Planting Site 1.

Site 2.
The slope on Site 2 was re-contoured by using a D-4 bulldozer following the same procedures that were outlined for Site 1 to minimize erosion. Soil used was from the surrounding area, especially from the area at the foot of the slope, to ensure continuity of both the physical and chemical properties with the surrounding undisturbed soil. A small berm was also created along the upper edge of the site next to the access road to redirect the water flow away from the site. Once site preparations were complete, surface preventative measures, including the use of straw flake dams, hand and mechanical pitting were utilized to minimize any remaining sheet flow runoff (Figure 14 and 15).

Eighty (80) native seedlings outlined in Table 1(page 17) and grown in the SERG shade house, were transplanted onto the slope (Figure 16). Planting occurred during the rainy season to help ensure survival. Plants were supplied with plant protection devices (treepees or tubex) to allow protection from herbivores and the elements. Weed mats were placed around the base of each plant to reduce weed growth and competition.

Site 2 Preparation and Planting.

Figure 14. Installation of straw flake dams on Site 3.

Figure 15. Installation of straw flake dams and hand pitting on Site 2.

Figure 16. Planting Site 2.

Site 3.
The area above Site 3 that is used for soil storage was contoured to form a smoother slope to help reduce possible erosion that could cause future damage to the site or the Fish Pond. The headwall on Site 3 was cut back to form a safer angle. In order to remove the headwall, approximately 10-20 feet of the upper flat area formerly covered by a chaparral community was cut back. The entire slope has experienced severe erosion, most probably caused by historic runoff from the bare mesa top directly to the southwest. Gullies were 2-4 feet deep and, in places, bedrock had been exposed. In order to repair this the eroded areas were filled in using the soil located atop the mesa. This was done in steps, as with Site 1, ensuring that each layer was moistened and cat-tracked for compaction before adding the next layer (Figures 17 and 18). In addition, an in-sloping terrace, located approximately two-thirds of the way up the slope, was constructed to help prevent any further runoff damage.

The use of jute netting, straw flake dams, and hand pitting of the slope was accomplished to help minimize future erosion activity. A series of straw bale dams were also installed along the top edge of the slope to prohibit sheet flow runoff that might occur from the mesa top (Figures 19 and 20).

Once site preparations were complete, approximately 200 native seedlings, from the species list outlined in Table 1 (page 17) and grown in the SERG shade house, were transplanted onto the slope (Figure 21). Planting occurred during the rainy season to help ensure survival. Plants were supplied with plant protection devices (treepees or tubex) to allow protection from herbivores and the elements. Weed mats were placed around the base of each plant to reduce weed growth and competition.

Site 3 Preparation and Planting.

Figure 17. Heavy equipment work on Site 3.

Figure 18. Heavy equipment work on steep slope of Site 3.

Figure 19. Insallation of jute netting on Site 3.

Figure 20. Jute netting installed on Site 3.

Figure 21. Planting Site 3.

Table 1.
Species Planted Listed By Site.

Monitoring and Maintenance

On Sites 1 and Site 3 a temporary gravity feed irrigation system was installed upon completion of planting to provide supplemental water for the seedlings during the hot summer months the first year after installation. Plants were also either given deep pipes to allow the water to reach the roots of the plants or basins to allow the water to percolate to the plants roots. All deep pipes were made of flexible pipe that was ridged to allow any animals that fell inside a means to escape. Certain plants along the edges of Sites 1 and 3, and the plants on Site 2 were not on an irrigation system but were watered, also by either a deep pipe or basin. Watering was done twice each month through the use of a 180-gallon portable, truck-mounted water tank and mechanical pump. The irrigation system and deep pipes were removed after one year.

All three sites were maintained for one year after implementation was completed. Maintenance included weeding as necessary by hand, mechanical, and the application of herbicide by a licensed professional. Hand weeding was also accomplished during watering trips. The application of herbicide was accomplished only once in spring 2002 due to the unusually dry year. In 2003 however, due to several large rainfalls that occurred throughout the rainy season, herbicide application occurred three separate times. Hand and mechanical weeding also took place twice in the spring of 2003.

It was discovered that Sites 2 and 3 had many native annuals and perennials growing on them from the initial seed bank. Site 2 had a large amount of native Hemizonia species throughout the entire site (Figure 22), as well as Chlorogalum species and Eremocarpus setigurus. Site 3 had several volunteer Lotus scoparius throughout the site. Mimulus aurantiacus and Salvia melifera, as well as annual Hemizonia and Plagiobothrys species were scattered throughout the site, however there was a large cluster of them at the top of the slope near the existing coastal sage scrub habitat (Figure 23). Plant protective devices were removed once the plants began to outgrow the containers so as not to deform the plants, or after one year. Plant protective devices were also removed in cases where the device was encouraging insect infestation (Figure 24). After the plant protector was removed from the plant, the insect problem disappeared (Figure 25).

Figure 22. Encelia californica, Hemizonia spp. and other native annual species on Site 2.

Figure 23. Native recruits on the top of Site 3.

Figure 24. Sambucus mexicana infested with insects, March 2002.

Figure 25. Sambucus mexicana formerly infested with insects, in May 2003.

There was severe coyote damage on the irrigation lines of both Site 1 and Site 3, with the greatest amount of damage occurring at Site 3 (Figure 26). Discussions with Chad Garber, Natural Resource Specialist for the Station, revealed that adult coyotes and their kits had been seen on the sites in the early morning, possibly living in one of the canyons nearby. Initially water was drained from all irrigation lines after watering in case the coyotes were attracted to the water inside the lines. When damage continued Ropel, a nontoxic spray that deters animals from damaging items by taste, was applied to half the lines on Site 3.

Figure 26. Damage to the irrigation lines caused by coyotes.

Additional Heavy Equipment Work
The area above Site 3 serves as a soil storage area. A large quantity of soil excavated from the Fish Pond was placed in this area creating a steep slope of loose soil with the potential to cause severe damage to Site 3 (Figure 27). Damage would be caused by soil eroding down onto the site and smothering the plants. This area was compacted and recontoured to create a milder slope with less runoff and erosion potential (Figures 28).

Figure 27. Steep ledge of loose soil at the top of Site 3.

Figure 28. Area above Site 3 after recontouring was done.

Site 1 had a similar problem. Soil that had been stored in the parking area above the site had been leveled out, creating a loose, steep ledge directly before the start of Site 1 (Figure 29). This soil also had the potential of eroding onto the site and damaging all or several of the plants. To keep this from occurring, the area of the slope was compacted and recontoured to create a more gentle slope, diminishing possible runoff and erosion damage (Figure 30).

Figure 29. Area of loose soil above Site 1.

Figure 30. Area above Site 1 after recontouring work was finished.

Results

Success Criteria
Success criteria includes both percent survival and growth of transplants. The success criteria to be met was that all sites would have 75% survival of all transplants after one year. Percent survival was taken one year after planting occurred. The survival for each site is seen in Table 2. It can be seen that the survival criteria of 75% was met for all three sites, with Site 1 at 77%, Site 2 at 92.5%, and Site 3, due to overplanting, at 100% (Figures 31, 32, 33, and 34).

Table 2.
Survival Criteria

Growth analysis was conducted at the end of one year. The plant volume (height*width*breadth) of each plant was measured when the seedlings were planted and compared to the plant volume one year later. The results of the plant volume can be seen for Sites 1, 2, and 3 in Table 3, 4, and 5, respectively. Plant volume is presented as both the total amount as well as the average for each species at the given site. The final plant volume is also presented in the same manner. However, the average is taken from the total number of plants initially installed on the site for a given species in order to take into account those plants that did not survive. Species were categorized as having either a linear or exponential growth pattern, depending on the species rate of growth over the one year period.

Table 3 shows the plant volume for Site 1. Mimulus aurantiacus had one hundred percent survival on the site, and had the largest increase in plant volume during the one year period. Encelia californica had the next highest increase, also with one hundred percent survival. Though percent survival for Lotus scoparius was lowest on the site (20%), plant volume still increased. Alternatively, Heteromoles arbutifolia had one hundred percent survival on the site, yet the change in plant volume was the smallest on the site (Figure31).

Table 3.
Site 1 Plant Volume by Species

Figure 31. Site 1 from the top after one year.

Table 4 shows plant volumes for Site 2 by species. Plant volume increased the most for Mimulus aurantiacus in the one year after planting. The lowest increase appeared in Rhus integrifolia. Both species had one hundred percent survival. Lotus scoparius and Malacothamnus fasciculatus were the only two species that did not have 100 percent survival, each with sixty percent survival. Both species still increased in plant volume, with Lotus scoparius having a larger increase in plant volume than Malacothamnus fasciculatus. Figure 32 shows Site 2 one year after planting.

Table 4.
Site 2 Plant Volume by Species

Figure 32. Site 2 after 1 year.

Table 5 displays the change in plant volume over one year for Site 3. Nassella pulchra had greater than ninety-six percent survival, and had the greatest increase in plant volume on the site. Rhus integrifolia had one hundred percent survival, but had the smallest amount of increase in plant volume on the site. Lotus scoparius had a survival rate slightly greater than twenty-six percent, however the plant volume still increased on the site (Figures 33 and 34).

Table 5.
Site 3 Plant Volume by Species

Figure 33 and 34. Site 3 one year after planting.

Of the three sites, Site 3 had the greatest total increase in plant volume, followed by Site 2 and then Site 1. Mimulus auranticus had one of the largest increases in plant volume on all three sites, followed by Nassella pulchra. Lotus scoparius had the poorest survival on all three sites, however, plant volume continued to increase for this species on all sites.

Discussion
Site 3 had a higher percent survival than Site 1 and 2. This high percent survival led Site 3 to have the largest total plant volume increase between the three sites. While the plant volume of individual plants may increase more on the other sites, the greater loss of plants on these sites leads to an overall reduction in plant volume.

Species were categorized as having either a linear or an exponential growth pattern. Plants that had linear growth patterns are the more woody plants such as Rhus integrifolia and Malasma laurina. These plants tend to grow slowly but at a constant rate over time. In this first year of growth, the species with a linear growth pattern increased at a lower rate than those species with exponential growth patterns.

Species with exponential growth patterns are species that initially grow very rapidly. These plants tend to be grass-like such as Nassella pulchra and Sisyrinchium bellum, or species that die back slightly during the dry season, then grow and spread rapidly during the rainy season such as Encelia californica and Mimulus aurantiacus. Lotus scoparius also exhibits an exponential growth pattern, however this is not reflected in the results due to the high amount of loss of this species.

Two species, Nassella pulchra and Mimulus aurantiacus, experienced the largest increases in plant volume over the one year period. This is to be expected as both of these species exhibit an exponential growth pattern. Additionally, many of the plants of these species were small when they were initially installed on the sites. This can be seen in the initial plant volume of Mimulus aurantiacus being around 1m3 for all three sites, and less than 1m3 for Nassella pulchra for Sites 2 and 3. These plants were also fairly young; approximately one year old. Very young and small plants of these species tend to grow a great deal during their first few years of life. Due to the small size and young age which these species were planted, a large increase in plant volume is not unexpected.

The Mimulus aurantiacus grew very large considering its small initial size in the one year time frame. This may be due to the initial potting soil which the seedling were grown. This species, as well as Nassella pulchra and Lotus scoparius, were grown in Vermiculite, while the other species were grown in Perlite. Vermiculite may encourage the roots to grow out of the planting mix faster after they are installed, however further studies are necessary to determine if this is true.

While Lotus scoparius did not see a great increase in plant volume, it also had rather poor survival, ranging from 20% to 60%, depending on the site. With such low survival rates, a total increase in plant volume of the species shows that the plants that did survive had a fairly large increase in plant volume. This species was also fairly small when planted and was initially started in potting soil made with Vermiculite. Lotus scoparius is a short lived perennial, so die off from this species is not unexpected. However, it also tends to reseed itself fairly well, and in the upcoming years it would not be unusual to see several seedlings of this species appearing on the sites.

There is also the possibility that some soil dredged up from the bottom of the Fish Pond was accidentally used on the sites. Discussions with JoEllen Kassebaum, Botanist for the Station, show that this soil has been known to allow plants to grow at an increased rate over normal conditions.

Management Implications
During the duration of the project weed control was accomplished as necessary. Due to the widely spaced rain patterns throughout November 2002 to April 2003, weeding was done on several different occasions. While this may have greatly reduced the seed bank of the weeds on the sites, it may be beneficial to continue weed control in the upcoming winter and spring months. Several native annuals and seedlings have appeared on the site, it would be beneficial to have any weed control done by someone familiar with native plants.

A few areas aadjacent to the three sites have the potential for erosion damage. Below Site 2, along the road that runs parallel to the Fish Pond, two areas of the hill have been dug back, creating a steep slope where minor erosion damage has already been caused by runoff (Figures 35 and 36). If retaining walls were built in these areas the potential erosion damage could be eliminated. Another possibility would be to use straw wattles across the top edge and at regular intervals down the slope to decrease the velocity of the water running down the slope.

Figure 35. Erosion below Site 2, near the junction of the two roads.

Figure 36. Erosion below Site 2, at the easternmost edge of the site.

At the base of Site 3 a section of the slope was not covered with jute netting because a retaining wall was scheduled to be built in this area (Figure 37). Because the area had no jute netting covering it, minor erosion from runoff has occured. This erosion damage could potentially increase if left as is. A retaining wall in this area would eliminate possible future erosion damage. An alternative plan would be to cover the small section of slope with jute netting and seed or plant with native plants.

Figure 37. Erosion damage at the base of Site 3.

On Site 3, one section of jute netting did not overlap and gaps appeared between the two pieces of jute netting. These gaps ended where the staples held the two pieces of jute together, as seen in Figure 38. Future jute netting should be overlapped more to avoid such gaps and the potential erosion problems associated with them.

Figure 38. Jute gapping on Site 3.

Many of the plants on the drip lines were installed with deep pipes. Due to the slow rate at which the water was released from the emitter and the high amount of clay in the soil it was found that drip lines and deep pipe were more of a hindrance than a benefit. The primary reason was that constant coyote damage on the site continued to alter the length of the line and made it increasingly difficult to line up the drip line into the deep pipe.

It is uncertain whether the drip lines that were sprayed with Ropel led to a decrease in damage caused by the coyotes. No data was taken prior to the spraying of the lines on how much damage was done, primarily because there had been no plan to use Ropel until coyote damage continued even after water was drained from the drip lines after use. Also, damage was much higher on certain occasions than on others, and the greater damage was interspersed with periods of lighter damage. Further study of this product would be useful to determine if it will greatly reduce coyote damage to drip lines. It may also be useful to apply the Ropel immediately after installation of the drip lines, as this may deter the coyotes from chewing on the drip lines immediately and eliminate the majority of damage to the lines.

Site 3 had several Lotus scoparius, Mimulus and Salvia species seedlings as well as several different native annuals growing along the top portion of the slope. When construction was done on the site, a portion of the soil supporting native plants along the top edge of the slope was cut back in order to reduce the slope of the site. This soil was then spread across the hillside, and the seed bank included in the soil was spread as well. Proper weather conditions allowed the seeds to germinate, grow and thrive. Some of these recruits also benefited from watering of nearby plants installed on the site. The growth of these recruits shows how beneficial it is to utilize the topsoil from an area populated by native species that needs to be removed.

Over the next several years the plants on these three sites around the Fish Pond should grow larger and fill in the sites. Hemizonia and other native annuals will help deter foot traffic through these locations during the spring and into the summer months. This will reduce or eliminate the amount of erosion and damage to the sites. Future weed control and erosion control in the areas mentioned will assist the sites to prosper.