American River Levees

Tree roots can provide some protection from erosion at low flows, but under higher conditions they may be a liability. For example, at high flows water may rise into the canopy of many trees within the parkway. When high velocities push against the canopy of trees the resulting forces can pull the entire tree out of the ground leaving a hole, accelerating erosion, and potentially compromising the levee. Additionally, high velocities around tree trunks may cause turbulence downstream which creates erosion. For these reasons trees are restricted from some areas near the levees.

But these are not the reasons why trees are being removed in our current work areas. The trees are being removed because in most cases rock protection cannot be properly installed around existing vegetation therefore it must be removed within the construction footprint (see question above).After construction the area will be replanted with native trees, shrubs, and grasses to gain the erosion and habitat benefits that they afford.

Unfortunately, wildlife is often displaced as a result of vegetation removal in advance of construction activities. However, these activities are timed to occur during the fall and early winter, typically the non-breeding season, when the level of impact/displacement to wildlife would be minimal. The wildlife that inhabited these areas are expected to move to adjacent habitats upstream and downstream of the construction footprint. This displacement is expected to be temporary until construction and habitat restoration activities have completed.

To mitigate the impacts to wildlife that occur as a result of habitat removal, two to three times the amount of habitat will be replaced and protected in perpetuity per the opinions of the resource agencies. This mitigation approach significantly increases the amount of habitat available to wildlife and is a way of helping to offset the temporal impacts to wildlife. The habitat mitigation provided onsite will typically completely replace the impacted habitat and depending on the bank protection design may increase the amount of available habitat compared to the original impact. The remaining habitat mitigation must be fulfilled at an “offsite” location in as close proximity to the impact site as feasible.

The vegetation establishes relatively quickly with intensive maintenance in the first 3-5 years, and it will not be long before wildlife can reclaim the area. The bank protection sites implemented during the late 90’s and early 2000’s have demonstrated that successful habitat is achievable.

Advanced computer modeling is used to determine how the river will behave and where erosion is likely to occur under high water conditions. These models are studied to determine the best location to place protective features and control erosion which could threaten the levees. Sometimes the best place to put protective rock features is not on the levee but along the riverbank near the water’s edge.

Haul trucks and other construction equipment need to use or cross portions of recreational trails located within the American River Parkway to move materials to the construction and mitigation sites. In areas where construction equipment is required to only cross an existing trail, flaggers would be present to direct traffic. Where larger portions of a trail are impacted or required for construction access, the trail would be temporarily rerouted away from the construction area. Any required detours would be developed in consultation with the City of Sacramento and Sacramento County Regional Parks.  Signage would be posted at the affected locations a minimum of 14-days in advance.

The on-site mitigation goal is to ensure that plantings associated with the revegetation of the levee provide a robust habitat for native species and are fully compatible with the surrounding environment. The erosion protection improvements will include the construction of a planting bench along the waterside toe of the levee to support on-site mitigation that includes trees and shrubs. The tree mix will include Boxelder, White Alder, Oregon Ash, Sycamore, Cottonwood, Oaks, and Willows. Complementing the tree plantings will be a variety of native shrub species that include mugwort, button bush, wild rose, sandbar willow and wild grape, as well as groundcovers that extend further up the slope of the waterside levee.

On-site mitigation typically can survive elevated flows however if elevated flows cause damage and plantings need to be replaced during the establishment period, the project partners will replace them. (Continue reading FAQs for more information regarding on-site mitigation, and visit the ARCF 2016 Mitigation web page.)

Elderberry plants, which provide habitat for the protected Valley Elderberry Longhorn Beetle, are being relocated and transplanted to off-site mitigation sites. In addition, the project is planting approximately 55 acres of new Elderberry habitat within the parkway.

The offsite mitigation sites include Rio Americano East and West, Rossmoor East and West, Glenn Hall/Paradise Beach, and the American River Mitigation Site as shown on the map below. Additional mitigation information can be found at the ARCF 2016 Mitigation web page.

The mitigation site plantings will include a broad variety of native trees and bushes which vary by site. The tree species will include a mixture of Sycamore, Cottonwood, Valley Oak, Interior Live Oak. Bush and plant species will include, among others, Coyote Brush, Western Redbud, Rose, Coffeeberry, Elderberry, Clematis, Western Goldenrod, Evening Primrose, Mugwort, Rose, Yarrow, Deergrass, and Creeping Wildrye.

The erosion protection sites include instream woody material that is tied down at the riverbank. It is intended to stay in place and provide habitat for juvenile fish migrating downstream. As the planted vegetation grows the instream woody materials will degrade through natural processes and their function will be provided by the new mature, live vegetation.

Typically, site preparation begins between October – May with trimming and/or removal of vegetation located with the construction footprint. Bank protection construction usually occurs between May and November, outside of flood season. On-site planting typically follows in the spring and summer following the completion of the riverbank construction. In general, work hours are Monday through Saturday from 7:00 a.m. to 6:00 p.m. for locations within the city of Sacramento and Monday through Friday from 6:00 a.m. to 8:00 p.m. and Saturday from 7:00 a.m. to 8:00 p.m. in the unincorporated areas of the county.

Neighborhoods located near project areas will be notified of specific work hours, haul routes, ingress and egress points, staging areas, detours, lane closures (if any), and affected recreational facilities(including bike paths) prior to the commencement of construction activities.

The construction roadway through Glenn Hall Park will remain until completion of the work near I-80 bridge. The construction roadway through the park is now being used by Caltrans and their contractor, Granite construction. When C3A beings work in the spring of 2024, GHP will be used to egress from the work site at I-80 bridge.

In order to revegetate the sites and restore their natural beauty, topsoil must be protected from runoff erosion until grasses and other vegetation can take root. This is done with erosion control fabric and fiber rolls which are held in place by stakes. The protective devices were designed for the current rain and high water conditions, and they are doing a good job protecting the site. The fabric, fiber rolls and stakes are all biodegradable and will last long enough for vegetation to establish before deteriorating. (The green stakes may appear to be plastic, but they are biodegradable and will degrade into water, C0₂ and compost.).

The recently completed projects sites will be fully revegetated in subsequent “greening” contracts. Revegetation of the levee slope and riverbank typically occurs in the springtime, following completion of the erosion protection construction. The on-site mitigation and plant establishment is monitored and maintained as needed by the project sponsors for 3 to 5 years.

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