Best Management Practices
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Best Management Practices
Level IA: FundamentalsEducation 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 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
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.
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
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 Road StabilizationDefinitionTravel way constructed as part of the construction plan including access roads, subdivision roads, parking areas, and other on-site vehicle transportation routes
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 velocityDi
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
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
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
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
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
Construction plans and drawings should be prepared by professionals familiar with the use of gabionsShould be securely keyed into the foundations and abutment surfaces
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 sediment pollution
Grade Stabilization StructureDesign CriteriaStructures designed in accordance with sound engineering practices can be constructed of concrete, rock, masonry, steel, aluminum, treated woodTypes - straight drop, drop inlet, box inlet, chute spillwayCapacity Conditions of adjacent areas is considered when determining the storm frequencyResidences/c