NC DOT by dffhrtcv3

VIEWS: 5 PAGES: 54

									Best Management
Practices (BMPs)
               Temporary Silt Fence
1605.01   •Reduces water flow and retains sediment on-site
          •Overlap splice joints 18 inches
                                    •Optional outlet using
                                  Special Sediment Control
                                   Fence (Max width=6 ft)
                                  •Shift outlet to low point
                                             3-6 ft
1605.01
          Temporary Silt Fence
             Special Sediment Control
                       Fence
1606.01

          • Reduces water flow and retains
            sediment
          • Used where flows and sediment loads
            will be too great for silt fence


                                      Often used
                                        by ESAs!
1606.01
           Special Sediment Control Fence
          • Not to be placed in areas determined to
            be wetlands without proper permits




                                  Fold in 4 ft. wire mesh
                                  (24 gauge--1/4-in. opening)
1622.01
            Temporary Slope Drain with
                 Earthen Berm
          • Carries concentrated runoff down a cut or fill
            slope without causing erosion
          • 12 in diameter flexible pipe
          • Sediment storage must be provided at top of
            slope near inlet or at outlet if slope drain
            discharges directly offsite w/o basin or trap
1622.01
          Temporary Slope Drain w/ Earthen Berm
1622.01
          Temporary Slope Drain w/ Earthen Berm
1622.01
          Temporary Slope Drain w/ Earthen Berm
1622.01
           Temporary Slope Drain with
                Earthen Berm
          • Anchor stakes placed on 10’ max. spacing
1622.01
             Temporary Slope Drain
          • Proper Installation—Inlet Protection
               Temporary Slope Drain
1622.01



          • Proper Installation—Outlet Protection
          Temporary Silt Basin – Type B
1630.02
          • Collects sediment flowing through a
            drainage way
          • Used with rock silt checks to slow flow
1630.02   Temporary Silt Basin – Type B




          Interior sideslopes 1.5:1 or flatter
              Temporary Rock Silt Check-
1633.01                Type A
          • Small dam with weir
            outlet
          • Constructed of Class B
            Stone and Sediment
            Control Stone
          • Usage
             – Outlet of slope drain
             – In ditches and channels
             – Can lead off-site
          • Naturally formed storage
            area traps sediment
Temporary Rock Silt Check-Type A
Polyacrylamide (PAM) for Turbidity Control

• Water soluble synthetic polymer of acrylamide
• Forms: dry powder, solution, emulsion, logs
 Suspended
 Silt & Clay


               PAM   No PAM

Add (PAM)




Flocs Form,
   Settle
       Keys to Making PAM
          Work for You
• Match PAM to your soil or suspended
  sediment and water chemistry.
• Reduce sediment load prior to PAM
  treatment.
• Keep the PAM logs moist.
• Create high flow onto PAM.
• Create high mixing (turbulence) after
  PAM.
• Allow for settling post-treatment.
Rock Check Type A with PAM




  •Coir or Excelsior matting may be used
  •Place matting on the sediment control stone
     Reapply PAM after rainfall of ½ in




3 ½ oz PAM
       Wattles with PAM
• Potential substitute for Rock Silt Checks
• Selected checks will be replaced as shown on
  plans or directed by Engineer
• Selected usage on Trout Waters and other ESAs
• Involve application of Polymer to aid in
  turbidity reduction of project runoff
        Typical Installation Materials




Metal sod staples
   and mallet

                             Erosion control blanket
                             (unless ditch is already
                                  lined with it)



24” long wooden     Wattle
     stakes
             Installation Guide


                    Is there a gap at
                      the upturned
                       edge of the
                         wattle?
  Weave wire                            Fill gaps with
staples through                         excess fabric
mesh at an angle
 to the wattle-
space every 1 ft.
             4 oz. (1/2 cup) PAM




Sprinkle 2 oz.
of PAM 705 on
the weir
                     Between here…           and here
(lower, center
                                     1 oz.
portion) and 1
oz. on both                          2 oz.
sides of the
weir where
water is going                       1 oz.

to flow over.
             Temporary Rock Sediment
1634.02           Dam – Type B
          • Small dam with weir
            outlet and built-in
            sediment basin

          • Constructed of Class
            B Stone and
            sediment control
            stone
 °
 °
 °° °°
       °
       °   Rock Pipe Inlet Sediment Trap
   °°°
1635.01            –Type A & B
       • Prevents sediment from entering pipe structure
       • Receives water from more than one direction
 °
 °     °
       °
 °° °°
           Rock Pipe Inlet Sediment Trap
   °°°
1635.01

                      –Type A




                       Class B
 °
 °     °
       °
 °° °°
   °°°
1635.02    Rock Pipe Inlet Sediment Trap
                      –Type B




                         Class A

                So it can be located within 30 ft of travel lane!
 ° °°° °
A°
 ° °
            Rock Inlet Sediment Trap –
 ° °°° °
 ° °   °
 1632.01            Type A & B
           • Stone dam built around a drop inlet
           • Slows flow creating a pool for settling of
             sediment
 ° °°° °
A°
 ° °
 ° °°° °
 ° °   °   Rock Inlet Sediment Trap – Type A
 1632.01




                              Class B Stone
 ° °°° °
B°
 ° °
 ° °°° °
 ° °   °   Rock Inlet Sediment Trap – Type B
 1632.02




                                              Class A Stone




                So it can be located within 30 ft of travel lane!
 ° °°° °
C° °
 ° °
            Rock Inlet Sediment Trap –
 ° °°° °
 ° °
 1632.03              Type C
           • Small protective structure around an
             inlet that receives light to moderate flow
           • Slows flow creating a pool for settling of
             sediment
           • Can be located
             within 30 ft of
             travel lane
 ° °°° °
C° °
 ° °
 ° °°° °
 ° °
 1632.03   Rock Inlet Sediment Trap – Type C
        Summary-Rock Inlet
          Sediment Traps
                Type A        Type B         Type C
                  ° °°° °
                 A°
                                ° °°° °        ° °°° °
                  ° °
                  ° °°° °       ° °
                               B°
                                ° °°° °        ° °
                                              C°
                                               ° °°° °
                  ° °   °
                  1632.01
                                ° °   °
                                1632.02
                                               ° °   °
                                               1632.03
Structure                                    Hardware
Material          Class B       Class A     cloth/T-post
Sediment
control stone      Yes           Yes            Yes
Dist. from
travel lane       >30 ft.       <30 ft.       <30 ft.
Min. volume     3600 ft3/ac   3600 ft3/ac   3600 ft3/ac
   Surface Outlet (Skimmer)
• Skimmer is a dewatering device
• Primary dewatering during a storm event occurs
  over the emergency spillway.
• Opening in ‘C’ points towards the dam
Skimmer Basin with Baffle
          Emergency Spillway
•Line with Type 4 filter fabric for drainage
•Overlap seams 18 inches
•Secure edges in 5” deep trench and compact
•Secure fabric with 6” metal staples; 3 ft spacing
•Size weir length (width) per plan
•Significant rain should activate emergency spillway




                                              Weir Length (Width)
Skimmer Basin with Baffle
                           Skimmer
•Minimum barrel diameter = 4 inches
•Ensure orifice/plug are sized per plan
   -Example: 3-inch skimmer orifice
   with 2.5-inch plug
   -Contractor must insert “knock out
   plug” with 2.5 inch hole drilled in it
   into the 3 inch orifice


Orifice

                                            Knock out plug
     Porous Baffle Spacing




• Baffles required in silt basins and all other
  temporary rock sediment dams:
   – If basin length ≤ 10 feet; 1 baffle
   – If basin length between 10 -20 feet; 2 baffles
   – If basin length > 20 feet; 3 baffles
                        Riser Basin
1630.01
          • Serves large drainage areas with concentrated
            flows where other BMPs are inadequate
          • Riser pipe with skimmer drains the basin
          • Stabilized overflow spillway for excess runoff
1630.01   Riser Basin
1630.01                  Riser Basin




     •    Must have overflow spillway
     •    Top of riser is below bottom of spillway
     •    Attach skimmer 1 ft off bottom of riser
     •    Stabilize discharge outfall
     •    Anti-flotation materials required at base of riser
Infiltration Basin w/ Baffles
• Rectangular basin (L:W ratio of 3:1-5:1)
• 1-3 coir baffles, equally spaced
• Requires porous sandy soils
• Drainage area < 10ac
• Outlet devices
   – Infiltration
   – Weir (emergency spillway)
• Dug into ground or built above ground
Guidelines for Infiltration Basins
• Must be in Coastal Plain according to
  Major Soil Regions of NC Map in the Land
  Quality Design Manual
                  Scour Hole
• Riprap depressions located at outlet of pipe
• Designed to dissipate energy and promote diffuse flow
• Outfall area must be installed per the plans—some show
  depression, others show flat
         Level Spreader
                   Consist of a trough with a level
                   non-erosive lip

                   Purpose: provides a non-erosive
                   outlet for concentrated runoff by
                   diffusing the water
                   uniformly across a stable slope


Water Quality Benefits:
  •increases stormwater infiltration
   •mitigate downstream erosion and ponding
   •reduce the water velocity, which allows larger
   particles to settle
Maintenance for All Devices
Clean out sediment at ½ design capacity
Do Not Change These EC Items:
1. Riser Basin incl. Skimmer Basin (fmr. Type A Silt Basin) –
  (Roadside Environmental Unit (REU) will Consult
  Hydraulics Unit.)
2. Temp. Rock Sediment Dams, Type A
3. Temporary Rock Sediment Dam, Type B – Located At
  Stream Crossings or Drainage Turnouts.
4. Temporary Rock Silt Check—Type A
5. Culvert Construction Sequence – (Consult with Resident
  1st; REU Will Consult Hydraulics Unit if necessary.)
6. Stream Channel Changes – Temporary or Permanent
  (Resident Engineer and REU will Consult Hydraulics Unit
  and PDEA.)
To order NCDOT Specifications and Std. Drawings:
www.ncdot.gov/business/order/puborder

								
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