Best Management Practices

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Best Management Practices. Structural Measures – Level II: Introduction to Design Education and Certification for Persons Involved in Land Disturbing Activities. Issued May 2009. The Manual for Erosion and Sediment Control In Georgia. Referred to as the Manual or Green Book - PowerPoint PPT Presentation

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  • Best Management Practices

    Structural Measures

    Level II: Introduction to DesignEducation and Certification for Persons Involved in Land Disturbing Activities

    Issued May 2009

  • The Manual for Erosion and Sediment Control In GeorgiaReferred to as the Manual or Green BookChapter 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 GSWCCs website at www.gaswcc.georgia.gov under Programs Urban Lands New Updates to the Manual for Erosion and Sediment Control

    Page includes newly approved practices, approved products list and other associated documents.

  • Best Management PracticesDefinitionVegetative measures & structural measures Properly designed, installed, & maintained in accordance with specification in the Manual for E&S ControlProvide effective erosion prevention & sedimentation control

  • Check DamDefinition A small temporary barrier constructed across a swale, drainage ditch, or area of concentrated flow

    PurposeReduce velocityFilter sedimentStabilize grade

    Not to be used in a live streamCd

  • Check DamDesign Criteria

    There is no formal design. The following standards shall be used:Drainage area shall not exceedTwo (2) acres for stone check damsOne (1) acre for haybales

    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

  • Check DamDesign How to Compute L:L = Height of Cd / Slope as decimal

  • Check DamExample problemIndependence School School RoadSlope From Topo = 5% 13%

    Find length between check dams for5%10%13%

  • Check DamSolutionL = 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.

  • Check DamExample

  • Channel StabilizationDefinitionImproving, constructing, or stabilizing an open channel or waterway

    PurposePrevent erosion and sediment depositionProvide adequate capacity for flood water, drainage, or other water management practicesCh

  • Channel StabilizationDesign CriteriaTypical linings include vegetation, riprap, and concreteLining selection depends on the velocities within the channelVegetative lining shall be established using erosion control blankets or matting or sodCh

  • ChChannel StabilizationFor Design Velocity

    0 - 5 Ft/SecVegetation (Ds3, Ds4, Mb)5 - 10 Ft/SecRock Riprap (Appendix C) > 10 Ft/SecConcrete

    Grade stabilization structures may be needed to reduce velocities

  • Channel StabilizationCh

  • Channel StabilizationExample

  • Construction ExitDefinitionStone 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.

    PurposeTo reduce or eliminate the transport of mud from construction area.Co

  • Construction ExitDesign CriteriaNo 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 areaCo

  • Construction ExitCo

  • Construction Road StabilizationDefinitionTravel way constructed as part of the construction plan including access roads, subdivision roads, parking areas, and other on-site vehicle transportation routes

    Cr

  • Construction Road StabilizationDesign Criteria6 coarse aggregate applied immediately after gradingGeotextile applied for additional stabilityGrades should be < 10% for slope lengths less than 200 ftRoad Widths:14 ft for one-way traffic20 ft for two-way traffic24 ft for trailer trafficCr

  • Construction Road StabilizationGeotextile underliner

  • Stream Channel DiversionDefinition A temporary channel constructed to convey flow around a construction site while a permanent structure is being constructed within a streambed.

    PurposeTo protect the stream channel from erosion and allows work in the dry.Dc

  • Stream Channel DiversionDesign CriteriaDrainage 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 greaterDc

  • Stream Channel DiversionDesign CriteriaSide slopes shall be no steeper than 2:1Table 6-12.1 gives channel linings and acceptable velocities. Note differences from channel stabilization.Dc

  • Stream Diversion ChannelStream Diversion Channel LiningsLining MaterialAcceptable VelocityGeotextile/0 - 2.5 fps polyethylene film or sodGeotextile alone2.5 - 9.0 fpsType 1 Riprap &9.0 - 13.0 fps GeotextileDc

  • Stream Channel Diversion

  • Diversion DefinitionA ridge of compacted soil, constructed above, across, or below a slope to safely convey runoff to a stable outlet

    PurposeTo 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

  • 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 settlementChannel Design Land slope must be taken into considerationDi

  • DiversionSelection of design storm based on type of diversionto be usedTemporary10-yr, 24-hr stormPermanent25 or 50-yr, 24-hr stormDi

  • Diversion

  • Temporary Downdrain StructureDefinitionA temporary structure used to convey concentrated storm water down the face of cut or fill slopes.

    PurposeTo safely conduct storm runoff from one elevation to another without causing slope erosion and allowing the establishment of vegetation on the slope.Dn1

  • Temporary Downdrain StructureDesign CriteriaThere is no formal design. The following standards shall be used:Placement located on undisturbed soil or well compacted fillDiameter provide sufficient capacity required to convey the max runoff expected during the life of the drainSized according to its contributing drainage area* 0.3 Ac = 10 in. * 0.5 Ac. = 12 in. * 1.0 Ac. = 18 in.Dn1

  • Temporary Downdrain StructureCommonly 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 outletDn1

  • Dn1

  • Temporary Downdrain Structure

  • Temporary Downdrain StructurePlacement

  • Permanent Downdrain StructureDefinition A permanent structure used to safely convey surface runoff from the top of the slope to the bottom of the slope.

    PurposeMinimize erosion due to concentrated storm runoff on cut of fill slopesDn2

  • Permanent Downdrain StructureDesign 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

  • Permanent Downdrain Structure

  • Filter RingDefinition A temporary stone barrier constructed at storm drain inlets and pond outlets.

    PurposeReduces 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

  • Filter RingDesign CriteriaThere 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 inches10-15 inches in diameter for pipes with diameters greater than 12 inches

    Height no less than two feet from gradeFr

  • Filter Ring

  • Filter RingExample

  • 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 slopesGabionGa

  • Design Criteria

    Construction plans and drawings should be prepared by professionals familiar with the use of gabionsShould be securely keyed into the foundations and abutment surfaces

    GabionGa

  • GabionExamples

  • Grade Stabilization StructureDefinition Structure used to stabilize the grade in natural or artificial channels

    PurposePrevent the formation or advancement of gullies and reduce erosion and sedimen