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STANDARD AND SPECIFICATIONS FOR PAVED FLUME Flipbook PDF
August 2005 Page 5B.33 New York Standards and Specifications For Erosion and Sediment Control STANDARD AND SPECIFICATION
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STANDARD AND SPECIFICATIONS FOR PAVED FLUME Anchor Lugs – Space anchor lugs a minimum of 10 feet on centers for the length of the flume. They will extend the width of the flume, extend 1 foot into subsoil, be a minimum of 6 inches thick, and be reinforced with #3 reinforcing bars placed on a 6-inch grid. Concrete – Minimum strength of design mix shall be 3000 psi. Concrete thickness shall be a minimum of 6 inches reinforced with #3 reinforcing bars. Mix shall be dense, durable, stiff enough to stay in place on steep slopes, and sufficiently plastic for consolidation. Concrete mix should include an air-entraining admixture to resist freeze-thaw cycles. Cross Section – Flumes shall have minimum depth of 1 foot with 1.5:1 side slopes. Bottom widths shall be based on maximum flow capacity. Chutes will be maintained in a straight alignment because of supercritical flow velocities.
Definition A small concrete-lined channel to convey water on a relatively steep slope.
Purpose To convey concentrated runoff safely down the face of a cut or fill slope without causing erosion.
Condition Where Practice Applies Where concentrated storm runoff must be conveyed down a cut or fill slope as part of a permanent erosion control system. Paved flumes serve as stable outlets for diversions, drainage channels, or natural drainageways, that are located above relatively steep slopes. Paved flumes should be used on slopes of 1:5 to 1 or flatter.
Design Criteria
Inlet Section – Design the inlet to the following minimum dimensions: side walls 2 feet high, length 6 feet, width equal to the flume channel bottom, and side slopes the same as the flume channel side slopes. Outlet Section – Outlets must be protected from erosion. Usually an energy dissipater is used to reduce the high chute velocities to lower non-erosive velocities. Rock riprap should be placed at the end of the dissipater to spread flow evenly to the receiving channel. See Figure 5B.17 on page 5B.35 for examples of outlet structures.
Capacity – Minimum capacity should be the 10-year frequency storm. Freeboard or enough bypass capacity should be provided to safeguard the structure from peak flows expected for the life of the structure. Slope – The slope should not be steeper than 1.5:1 (67%). Cutoff Walls – Install cutoff walls at the beginning and end of paved flumes. The cutoff should extend a minimum of 18 inches into the soil and across the full width of the flume and be 6 inches thick. Cutoff walls should be reinforced with #3 reinforcing bars (3/8”) placed on a 6-inch grid in the center of the wall.
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Drainage filters – Use a drainage filter with all paved flumes to prevent piping and reduce uplift pressures. Size of the filter material will be dependent on the soil material the flume is located in.
Invert – Precast concrete sections may be used in lieu of cast in place concrete. The sections should be designed at the joint to be overlapped to prevent displacement between sections. Joint sealing compound should be used to prevent migration of soil through a joint. Cutoff walls and anchor lugs should be cast in the appropriate sections to accommodate the design criteria. Small Flumes – Where the drainage area is 10 acres or less, the design dimensions for concrete flumes may be selected from those shown in the table on the following page:
Page 5B.33
New York Standards and Specifications For Erosion and Sediment Control
Drainage Area (Acres) 5
10
Min Bottom Width
4
8
Min Inlet Depth (ft)
2
2
Min Channel Depth (ft)
1.3
1.3
Max Channel Slope
1.5:1
1.5:1
Max Side Slope
1.5:1
1.5:1
3. Where drainage filters are placed under the structure, the concrete will not be poured on the filter. A plastic liner, a minimum of 4 mils thick, will be placed to prevent contamination of filter layer. 4. Place concrete for the flume to the thickness shown on the plans and finish according to details. Protect freshly poured concrete from extreme temperatures (hot or cold) and ensure proper curing. 5. Form, reinforce, and pour together cutoff walls, anchor lugs and channel linings. Provide traverse joints to control cracking at 20-foot intervals. Joints can be formed by using a 1/8 inch thick removable template or by sawing to a minimum depth of 1 inch. Flumes longer than 50 feet shall have preformed expansion joints installed.
See Figure 5B.18 on page 5B.36 for details.
Construction Specifications 1. The subgrade shall be constructed to the lines and grades shown on the plans. Remove all unsuitable material and replace them if necessary with compacted stable fill materials. Shape subgrade to uniform surface. Where concrete is poured directly on subsoil, maintain it in a moist condition. 2. On fill slopes, the soil adjacent to the chute, for a minimum of 5 feet, must be well compacted.
New York Standards and Specifications For Erosion and Sediment Control
6. Immediately after construction, all disturbed areas will be final graded and seeded.
Maintenance Inspect flumes after each rainfall until all areas adjoining the flume are permanently stabilized. Repair all damage immediately. Inspect outlet and rock riprap to assure presence and stability. Any missing components should be immediately replaced.
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Figure 5B.17 Examples of Outlet Structures
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Page 5B.35
New York Standards and Specifications For Erosion and Sediment Control
Figure 5B.18 Paved Flume
New York Standards and Specifications For Erosion and Sediment Control
Page 5B.36
August 2005