More often than not erosion control and habitat restoration go hand and hand. Especially when the habitat restoration takes place along an almost vertical bluff face with erosion gullies, and deeply incised barrancas. Until the native vegetation becomes established it must be protected. Unprotected, the bluffs would continue to erode and the vegetation, new and old, could end up at the bottom of those cliffs.

There is a seven acre site located in Newport Beach, California that has a long history of human intrusion, (with their often off-the-leash pets), via trails over the bluff face and rodent invasions, burrowing on slopes and uplands. The adjacent, non-irrigated, grasslands are relatively flat, but do slope toward the bluffs, and create numerous "hidden" watersheds.

When the County of Orange, Harbors, Beaches, Parks Department, took control of the land, a restoration project was launched. The goal of the project was to achieve a native habitat restoration by first minimizing human impact and then maximizing erosion control to allow the native vegetation to become re-established.

Site Conditions

The site recently underwent a successful habitat restoration project to restore native coastal sage scrub habitat to bluffs and barrancas.

The bluffs are covered with remnant patches of native vegetation consisting of Coastal Sage Scrub species, and mostly exotic, invasive weed species, i.e., mustard and tumbleweed, castor bean, tree tobacco and introduced European annual grasses. In addition, steep, barren slopes, gullies, and ravines characterize the site. The gullies and ravines are the result of human misuse and natural causes. These gullies and ravines, natural or man-made, continue to contribute to the ongoing erosion of the bluff face.

Erosion of the site is the result of three factors: man-made, natural and burrowing rodents. Man-made erosion resulted from the creation of numerous trails crisscrossing the face of the bluff. Creation of these trails for purposes of walking, jogging, climbing or mountain biking, naturally eliminated the existing native vegetation, and carved deep incisions into the bluff face, contributing to the naturally occurring erosion.

Natural erosion is the result of several “hidden” watersheds. Water flowing off the adjacent grassland concentrated in certain areas, such as the man-made trails. The trails, devoid of vegetation from continual human use, acted as channels and allowed the water to pick up velocity. The increase in velocity consequently increased the scouring effect of the water, further contributing to the overall erosion. Ground squirrels riddle the uplands and steep slopes, burrowing tunnels that catch water and result in upland sinks and slope washouts creating deep incisions in the bluff faces.

The signage at the Nature Preserve includes the upper Newport Bay Nature Preserve Monument sign.

It quickly became evident that in order to restore the Coastal Sage Scrub (CSS) Habitat along the bluff, erosion control and eliminating or reducing the effect of the contributing erosion factors would be of paramount importance. Erosion control then became a major factor in the habitat restoration program. As so often happens with restoration projects tied to a grant, funds and time to complete the project were limited.

There were various alternative solutions that were considered for the project, such as re-engineering the slope and turning it into a massive grading project. However, due to the funding and timing constraints, not to mention the major environmental impacts of such a solution, the idea of re-engineering of the slope was rejected.

It was decided to proceed with a minimum impact solution: a habitat restoration well-suited to the existing slope conditions, focusing on the elimination of unauthorized trail use, management of exotic and invasive weeds and rodents, re-vegetating with native plant material, and of course, erosion control measures to reduce and eliminate erosion to help reestablish the native plant material.

The Design Solution

One of the erosion control solutions for the project was the use of "smile" or chevron ditching and gravel bagging. The ditching was designed to catch and slow water movement and simultaneously collect loose sediment creating an inviting environment for plant growth. Gravel bagging works well in high water velocity situations, in that the weight of the bag resists displacement by the rushing water.

In order to restore the area, a team of professionals in charge of the project came up with design solutions that would have minimum environmental impact. The following erosion control prescriptions were applied to the project with successful results:

1) Steep trail beds and gullies - "smile" or chevron ditching and gravel bagging. The ditching was designed to catch and slow water movement and simultaneously collect loose sediment creating an inviting environment for plant growth. Gravel bagging works well in high water velocity situations, in that the weight of the bag resists displacement by the rushing water (and irate trail users). It also traps sediments, but allows the water to flow through, reducing its velocity in the process. The trapped sediment usually contains organic materials, which makes for a great seedbed. The gravel bags were also easy to carry and hand place in the small, close and steep confines of the trail beds. Bags were placed close together to prevent water from picking up speed between the bags. It was also important to ensure that the bags, or any other device, such as silt fencing or straw bales/wattles are properly keyed into the slope to prevent water from passing unimpeded under the erosion control device.

Part of the restoration process included the installation of straw wattles secured with wood stakes. After track walking the slopes, straw wattling is then applied. Straw wattling are tubes of rice straw held together with plastic netting. The wattles are about 25 feet long and weigh about 30 pounds, and are relatively quick and easy to install. Straw wattling is a very effective tool in the fight against erosion by slowing, spreading and filtering runoff which can prevent erosion from starting.

2) Steep bare slopes – slope tracking and contour straw wattling. Slope tracking is a process of running a dozer up and down accessible slope faces. The dozer tracks break the soil surface and in the process create depressions and ridges, mirroring the track in the soil, parallel to the slope face. Where feasible, this is a great technique for scarifying and prepping the soil prior to seeding. These depressions slow water down, collect and hold water creating a good place for seed to germinate. After track walking the slopes, straw wattling is then applied. Straw wattling are tubes of rice straw held together with plastic netting. The wattles are about 25 feet long and weigh about 30 pounds, and are relatively quick and easy to install. Rice straw wattles are preferred, as they do not break down as quickly as other straws, and will last through a typical three to five year plant establishment period.

Another straw wattle advantage is the fact that, unlike silt fencing for instance, the straw wattles can be left in place to eventually decompose. Straw wattling is a very effective tool in the fight against erosion by slowing, spreading and filtering runoff. This prevents erosion from starting. The captured sediment on the uphill side of the wattle makes an ideal seed bed, and often times the quickest and best seed germination and growth occurs here. However, the wattles, as well as any other erosion control method and/or product, must be installed correctly, and per any installation detail provided by the manufacturer. If the wattles are not properly keyed into the slope, if the ends of the wattles are not butted up tight against each other, or if they are not adequately secured with stakes, failure, i.e., erosion will occur. Another very important installation consideration is that the wattling must be installed on the contour. If it is not, flows will become channeled and concentrated along the wattle, and will eventually find a spot to jump over the wattle and cause erosion on the wattle’s downhill side.

Also, hydroseeding was installed in a two-step process for the habitat restoration. The first step included water, seed, mycorrhizal inoculum, and a minimum of BFM. Step two included water and BFM.

3) Eroded bluff face - the least accessible areas of the site, was hydroseeded with CSS seed, and then covered with Bonded Fiber Matrix (BFM). Hydroseeding with BFM limited any physical disturbance of the erosion prone bluff face. Gravel bags or straw wattling could not have been placed in these sensitive locations. Unlike even erosion control blankets, the BFM molds itself to any soil shape, ensuring good soil contact. With other erosion control methods, soil contact can become lost, resulting in the formation of rills in the soil, the first sign of erosion. Once BFM is applied to the soil, it dries to create a high-strength, porous and erosion resistant blanket.

4) Existing drainage inlet - water was actually bypassing an existing drainage inlet, causing erosion further down the slope. The area within the vicinity of the inlet was recontoured and swaled, with a small dozer, to direct run-off water directly towards the inlet. Straw wattling was actually used here to direct the run-off towards the inlet, and by creating a berm, to help contain the water around the inlet.

5) Hidden watersheds - The adjacent grassland slopes gently toward the bluff face. Close observation revealed low spots, or areas where water collected and concentrated, typically at the head of one of the numerous trails heading down the bluff. Gravel bags were placed along the slope hinge points to help slow the flow of water in these areas of concentration.

Planting Prescriptions

Cactus pad were planted among the erosion control devices to discourage the human use of the trails.

Plant materials used at the site were also a large part of the restoration. For trail beds and gullies, cactus pads were planted among the erosion control devices, and along the bluff top, to discourage the human use of the trails. The cactus pads themselves, planted the right way, acted as an erosion control device. Coastal Sage Scrub (CSS) species were hydroseeded, which included California sage, Artemsia sp., southern sun cup Camissonia sp., monkey flower, Diplacus sp., California bush flower, Encelia sp., goldenbush, Ericameria sp., buckwheat Eriogonum sp., cudweed, Gnaphalium sp., coastal goldenbush, Isocoma sp., goldfields, Lasthenia sp., deerweed, Lotus sp., lupine, Lupine sp., purple needlegrass, Nassella sp., owls clover, Orthocarpus sp., Phacelia, and sage. Salvia sp.. These native plants exhibit good erosion control qualities. Hydroseeding was applied in both directions, parallel and perpendicular to the slope, to ensure that the BFM coverage was thorough.

Erosion control techniques used on the slopes straw wattles on contours of steep slope face and shallow slope toe. Slope tracking is a process of running a dozer up and down accessible slope faces. The dozer tracks break the soil surface and in the process create depressions and ridges, mirroring the track in the soil, parallel to the slope face. Where feasible, this is a great technique for scarifying and prepping the soil prior to seeding. These depressions slow water down, collect and hold water creating a good place for seed to germinate.

With the combination of erosion control prescriptions and planting methods, the habitat restoration project at Newport Beach proved to be a challenging and ultimately rewarding experience for everyone involved. The County’s Harbors, Beaches and Parks Department staff employed several “low tech” approaches and techniques, which respected the existing topography and site features, versus the use of high impact grading and engineering, resulting in a successful habitat restoration project.