Opportunities for Vegetation on Levees and Berms

As mentioned earlier, many levees along the major streams are large enough to accommodate vegetation under the proposed revised vegetation guidelines.

Unrevetted Levees

Most unrevetted levees that have two-lane surfaced roads on the crown exceed the 30-ft. width requirement at freeboard that is proposed in the revised vegetation guide for retention of vegetation. Also, the waterward slope of the basic levee under the proposed revision has been changed from 3:1 horizontal to vertical, to 2:1 horizonal to vertical. This change increases the area at the waterward base of the levee where roots are allowed. This would provide for considerably more trees and shrubs near the waterward toe of the levee.

Unrevetted Berms

The proposed vegetation guide provides that where a berm exceeds 10 ft. in width, vegetation is allowed with no requirement for species, spacing, height, or pruning unless special conditions require some restriction.

Low Rock Revetment

In the case of the Steamboat Slough bank protection work, the CE constructed a 10-ft. berm just above the normal low water level and placed rock on the face of the berm. This is an example of innovative design of a levee to provide a condition where vegetation can be allowed. This design is consistent with the criteria for vegetation on berms established in the proposed revised vegetation guide. It should be recognized that this special construction feature increased the cost of providing flood control. In this case the CE and the State provided the funds to pay the extra capital costs. The local maintaining agency will be responsible for maintenance.

Low rock was also placed by the CE in several reaches of the Sacramento River downstream from Sacramento as early as 1940. In many locations vegetation has grown in and above the rock. Normal deterioration of the rock has resulted in some areas and repairs are needed, but very few problems have been attributed to the vegetation. The rock has reduced erosion and has not been significantly displaced in 40 yrs., indicating that low rock has been successful under these flow and soil conditions.