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Item No. 639

Rock Berm

639.1  Description

This item shall govern the construction of a temporary berm of open graded rock that is installed at the toe of a slope on the perimeter of a developing area.  The purpose of a rock berm is to intercept sediment-laden water from unprotected areas, to retain the sediment and to release the water in sheet flow.  This item shall also govern the removal of the “Rock Berm” and re-vegetation of the area.

639.2  SubmittalsThe submittal requirements for this specification item shall include:

A. Function (stream flow or other) and dimensions of the rock berm

B. Source, type and gradation of rock

C. Re-vegetation program, including:

1.  Identification of the type, source, mixture, Pure Live Seed (PLS) and rate of application of the seeding.

2.    Type of mulch.

3.    Type of tacking agent

.4.    Type and rate of application of fertilizer.

639.3  Design Criteria

A rock berm shall be constructed near the perimeter of a disturbed site within the development area. It is not to be constructed outside the property lines without obtaining an easement or written permission from the affected adjacent property owners.

A detailed design is not required for the installation of a rock berm; however, the following criteria shall be observed: 

Drainage area –  less than 5 acres.

Height             –  18 inches  minimum height, measured vertically from the top of the existing ground at the upslope toe to the top of the berm.

Top width        –  2 feet minimum.

Side slopes     –  2:1 or flatter.

Grade              –  Berms will be built along a contour as near possible to a 0 percent grade.

639.4  Materials

Surplus rock excavated from utility trenches or from other excavations may be used in construction of these berms.  In general, the rocks shall be sound with a minimum of 3 inches in smallest dimension and shall weigh between 10 and 30 pounds each.  Seeding for re-vegetation shall conform to, “Seeding for Erosion Control”.Use only open-graded rock of the size indicated on Standard Detail, with most of the fines removed.

639.5 Construction Methods

All trees, brush, stumps and objectionable material shall be removed and disposed in a manner that will not interfere with the construction of the berm.A trench shall be excavated to a minimum depth of 4 inches below existing grade for placement of the rock as indicated on Standard Detail and the Drawings.  The rocks shall be placed in interlocking layers with close joints starting at the base.  Open joints shall be filled with rock-spalled materials as required to stabilize the berm.The area upstream from the rock berm shall be maintained in a condition, which will allow sediment to be removed following the runoff from a rainfall event. After each rainfall event with an accumulation of 1 inch or more, an inspection of the rock berm will be made by the Contractor and the stone shall be replaced, when the structure ceases to function as intended because of silt accumulation among the rocks, washout, construction traffic damage, etc.When the silt reaches a depth equal to 1/3 the height of the berm or 6 inches, whichever is less, the Contractor will remove the accumulated silt and dispose of it at an approved disposal site in a manner that will not contribute to additional siltation.  The berm will be reshaped as needed during construction. When the site is completely stabilized, the berm will be removed and disposed of in a manner approved by the Engineer or designated representative.The area will be re-vegetated as required by Item, “Seeding for Erosion Control”.

639.6 Measurement

Acceptable work performed and prescribed in this item will be measured by the linear foot along the centerline of top of berm.

639.7  Payment

All work performed by this item will be considered subsidiary to other bid items unless it is included as a separate bid item in the contract documents then all work performed as required herein and measured as provided under “Measurement” will be paid for at the unit bid price.  The bid prices shall include full compensation for furnishing all labor; all materials; all royalty and freight involved; all hauling and delivering; and all tools, equipment and incidentals necessary to complete the work.  Payment will not be made for unauthorized work