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Best Management Practices

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  1. Best Management Practices • Structural Measures – • Level IB: Advanced Fundamentals • Education and Certification for Persons • Involved in Land Disturbing Activities Issued May 2009

  2. The Manual for Erosion and Sediment Control In Georgia • Referred to as the Manual or Green Book • Chapter 6 of the Manual focuses on the standards and specifications for planning, design and installation of erosion and sediment control measures. Updates to the Manual can be found on GSWCC’s website at under Programs Urban LandsNew Updates to the Manual for Erosion and Sediment Control • Page includes newly approved practices, approved products list and other associated documents.

  3. Best Management Practices Definition Vegetative measures & structural measures Properly designed, installed, & maintained in accordance with specification in the Manual for E&S Control Provide effective erosion prevention & sedimentation control

  4. Check Dam Definition A small temporary barrier constructed across a swale, drainage ditch, or area of concentrated flow Purpose Reduce velocity Filter sediment Stabilize grade Not to be used in a live stream Cd

  5. Check Dam Design Criteria There is no formal design. The following standards shall be used: Drainage area shall not exceed Two (2) acres for stone check dams One (1) acre for hay bales Height - the center of the check dam must be at least 9 inches lower than outer edge. Height should be 2 feet maximum measured to center of check dam. Cd

  6. Check Dam Design Graded 2”-10” How to Compute L: L = Height of Cd / Slope as decimal

  7. Check Dam • Example problem • Independence School – School Road • Slope From Topo = 5% – 13% • Find length between check dams for • 5% • 10% • 13%

  8. Check Dam Solution • L = Height of Cd / Slope as Decimal • L = 2 ft. / 0.05 = 40 ft. • L = Height of Cd / Slope as Decimal • L = 2 ft. / 0.10 = 20 ft. • L = Height of Cd / Slope as Decimal • L = 2 ft. / 0.13 = 15 ft.

  9. Check Dam Example

  10. Channel Stabilization Definition Improving, constructing, or stabilizing an open channel or waterway Purpose Prevent erosion and sediment deposition Provide adequate capacity for flood water, drainage, or other water management practices Ch

  11. Channel Stabilization Design Criteria Typical linings include vegetation, riprap, and concrete Lining selection depends on the velocities within the channel Vegetative lining shall be established using erosion control blankets or matting or sod Ch

  12. Channel Stabilization For Design Velocity 0 - 5 Ft/Sec Vegetation (Ds3, Ds4, Mb) 5 - 10 Ft/Sec Rock Riprap (Appendix C) > 10 Ft/Sec Concrete Grade stabilization structures may be needed to reduce velocities Ch

  13. Channel Stabilization Example

  14. Construction Exit Definition Stone stabilized pad located at any point where traffic will be leaving a construction site to enter a public right-of-way, street, alley, sidewalk or parking area. Purpose To reduce or eliminate the transport of mud from construction area. Co

  15. Construction Exit Design Criteria No formal design. The following standards shall be used: Aggregate size – stone in accordance with National Stone Association R-2 (1.5 to 3.5 inch stone) Pad thickness – gravel pad minimum thickness of 6 inches Pad width – minimum width should equal full width of all points of vehicular egress, but not less than 20 feet wide Pad length – minimum of 50 feet Washing - Wash tires if action of vehicles over gravel does not remove sediment. Divert tire washing to proper area Co

  16. Construction Exit Co

  17. Construction Road Stabilization Definition Travelway constructed as part of the construction plan including access roads, subdivision roads, parking areas, and other on-site vehicle transportation routes Cr

  18. Construction Road Stabilization Design Criteria 6” coarse aggregate applied immediately after grading Geotextile applied for additional stability Grades should be < 10% for slope lengths less than 200 ft Road Widths: 14 ft for one-way traffic 20 ft for two-way traffic 24 ft for trailer traffic Cr

  19. Construction Road Stabilization Geotextile underliner

  20. Stream Channel Diversion Definition A temporary channel constructed to convey flow around a construction site while a permanent structure is being constructed within a streambed. Purpose To protect the stream channel from erosion and allows work “in the dry”. Dc

  21. Stream Channel Diversion Design Criteria Drainage areas < 1 square mile (640 acres) Bottom width shall be a minimum of 6 feet or equal to the bottom width of the existing streambed, whichever is greater Dc

  22. Stream Channel Diversion Design Criteria Side slopes shall be no steeper than 2:1 Table 6-12.1 gives channel linings and acceptable velocities. Note differences from channel stabilization. Dc

  23. Stream Diversion Channel Stream Diversion Channel Linings Lining MaterialAcceptable Velocity Geotextile/ 0 - 2.5 fpspolyethylene film or sod Geotextile alone 2.5 - 9.0 fps Type 1 Riprap & 9.0 - 13.0 fps Geotextile Dc

  24. Stream Channel Diversion

  25. Diversion Definition A ridge of compacted soil, constructed above, across, or below a slope to safely convey runoff to a stable outlet Purpose To reduce the erosion of steep or otherwise highly erodible areas by reducing slope length, intercepting storm runoff and diverting it to a stable outlet at a non-erosive velocity. Di

  26. Diversion Design Criteria Location determined by outlet conditions, topography, land use, soil type, length of slope, seep planes, and the development layout A diversion consists of two components: Ridge Design – have stable side slopes, no steeper than 2:1 and minimum width of 4 ft at the design water elevation after settlement. Design shall allow 10% for settlement Channel Design – Land slope must be taken into consideration Di

  27. Di Diversion Selection of design storm based on type of diversion to be used • Temporary 10-yr, 24-hr storm • Permanent 25 or 50-yr, 24-hr storm

  28. Temporary Downdrain Structure Definition A temporary structure used to convey concentrated storm water down the face of cut or fill slopes. Purpose To safely conduct storm runoff from one elevation to another without causing slope erosion and allowing the establishment of vegetation on the slope. Dn1

  29. Temporary Downdrain Structure Design Criteria There is no formal design. The following standards shall be used: Placement – located on undisturbed soil or well compacted fill Diameter – provide sufficient capacity required to convey the max runoff expected during the life of the drain Sized according to its contributing drainage area * 0.3 Ac = 10 in. * 0.5 Ac. = 12 in. * 1.0 Ac. = 18 in. Dn1

  30. Temporary Downdrain Structure Commonly used in conjunction with Diversions (Di) Removed once the permanent storm water disposal system is installed and functioning Storm drain outlet protection (St), shall be placed at the downdrain outlet Dn1

  31. Temporary Downdrain Structure Placement Diversion Anchored every 10 ft Outlet protection and lined channel

  32. Permanent Downdrain Structure Definition A permanent structure used to safely convey surface runoff from the top of the slope to the bottom of the slope. Purpose Minimize erosion due to concentrated storm runoff on cut of fill slopes Dn2

  33. Permanent Downdrain Structure Design Criteria May be constructed of concrete, pipe, pre-fabricated sectional conduit or other adequate materials Should be designed by professionals familiar with these structures All structures shall satisfy GDOT Standards and Specs Shall safely convey the 25-yr, 24-hr storm Outlets must be stabilized Dn2

  34. Permanent Downdrain Structure

  35. Filter Ring Definition A temporary stone barrier constructed at storm drain inlets and pond outlets. Purpose Reduces flow velocities, preventing the failure of other sediment control devices. Prevents sediment from leaving the site or entering drainage systems, prior to permanent stabilization. Fr

  36. Filter Ring Design Criteria There is no formal design. The following standards shall be used: Location- Shall surround all sides of the structure receiving runoff and should be placed no less than 4 ft. from the structure. When placed in front of a retrofit it should be placed no less than 8-10 ft. from the retrofit Stone Size – Constructed of stone no smaller than 3-5 inches in diameter for inlets with diameters less than 12 inches 10-15 inches in diameter for pipes with diameters greater than 12 inches Height – no less than two feet from grade Fr

  37. Filter Ring

  38. Filter Ring Example

  39. Definition Gabions are large, multi-celled, welded wire or rectangular wire mesh boxes, used in channel revetments, retaining walls, abutments, check dams, etc. Purpose Used to stabilize steep or highly erosive slopes Ga Gabion

  40. Design Criteria Construction plans and drawings should be prepared by professionals familiar with the use of gabions Should be securely “keyed” into the foundations and abutment surfaces Ga Gabion

  41. Gabion Examples

  42. Grade Stabilization Structure Definition Structure used to stabilize the grade in natural or artificial channels Purpose Prevent the formation or advancement of gullies and reduce erosion and sediment pollution Gr

  43. Grade Stabilization Structure Design Criteria Structures – designed in accordance withsound engineering practices – can be constructed of concrete, rock, masonry, steel, aluminum, treated wood Types - straight drop, drop inlet, box inlet, chute spillway Capacity – Conditions of adjacent areas is considered when determining the storm frequency Residences/commercial 100-yr, 24-hr& recreation buildings Recreation & 25-yr, 24-hrlandscape areas Agricultural Land 25-yr, 24-hr Gr

  44. Grade Stabilization Example

  45. Level Spreader Definition A storm flow outlet device constructed at zero grade across the slope whereby concentrated runoff may be discharged onto stabilized ground and converted to sheet flow. Purpose To dissipate storm flow energy at the outlet by converting storm runoff into sheet flow and to discharge it onto areas stabilized by existing vegetation without causing erosion. Lv

  46. Lv Level Spreader Design Criteria • Length – Determined by 10-yr, 24-hr storm • Width – Minimum 6 feet

  47. Rock Filter Dam Definition A temporary stone filter dam installed across small streams or drainageways Purpose Capture and filter sediment for removal when working in a stream or water body. Reduce velocity of water. *The use of a rock filter dam in a stream is considered fill by the U.S. Army Corps of Engineers and is not allowed in their permit. Rd

  48. Rock Filter Dam Design Criteria There is no formal design. The following standards shall be used: Drainage area - shall not exceed 50 acres Height –should not be higher than the channel banks -center should be at least 6 inches lower than outer edge Slide slopes – shall be 2:1 or flatter Location – as close to the source of sediment as possible Stone size - determined by design criteria for Riprap Rd

  49. Rock Filter Dam Figure 6-18.1

  50. Retaining Wall Definition A wall constructed of concrete masonry, reinforced concrete cribbing, treated timbers, steel pilings, gabions, stone drywall, rock riprap, etc Purpose Used to stabilize cut or fill slopes where stable slopes are not attainable without the use of wall. Design Criteria Requires design specific to the site Re