tdot roadway design division - tn.gov...microsoft powerpoint - module 4.pptx author: ewoodson...
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© Arcadis 2017
TDOT Roadway Design Division
Module 4:
Outfalls
© Arcadis 2017
Outfalls - Definition• Stormwater runoff, snow melt runoff, and surface runoff and drainage• Stormwater must be in a discernable/discrete/confined conveyance
– pipes and culverts– ditches and channels– curb and gutter– catch basins or curb inlets (outfall or sub-outfall)
• May include the discharge of– sediment filter bags– dewatering structures
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• Leaves the project:– ROW– Project termini– Easement (i.e. temporary construction or permanent drainage)
• Directly enters TDEC jurisdictional features (streams, springs, wetlands and sinkholes) – Does not include ephemeral streams
Outfalls - Locations
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Outfall Examples
ENHANCED ROCK CHECK DAMS
EXISTING DRAINAGE SWALE
ROWClearing and Grubbing
Natural drainage features need to be protected
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DIVERSIONS
SEDIMENT TRAP
EXISTING DRAINAGE SWALE
Outfall Examples
Intermediate Grading
Natural drainage features need to be protected
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Outfall Examples
Final Stabilization
Rip rap channel to stream. ROW
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Outfall Examples
Multiple culverts discharging into a wet weather conveyance
ROW
TWO SEPARATE DISCHARGES
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Outfall Examples
Multiple discharges entering stream.
TWO SEPARATE DISCHARGES TO A STREAM
ROW
STORM DRAINAGE SYSTEM
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Outfall Examples
Natural drainage swales or toe ditches that discharge to streams
ROW
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ROW
Outfall Examples
Relocated stream channel discharging to another stream
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Outfall Examples
Pipe/culvert/ditch discharging at ROW or easement before entering offsite stream
ROW OR EASEMENT
STREAM
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Outfall Examples
Discharge from a sediment filter bag
STREAM
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Outfall Examples
Low area discharge in silt fence from sediment filter bag
ROW OR EASEMENT
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Sub-Outfalls - Definition• A sub-division of a main outfall to accomplish the
following:‒ To reduce the drainage area (eliminate need for
sediment basins and/or traps)‒ To account for drainage in a closed storm system
that is collected in area drains or curb inlets• Closed drainage system directly discharges to a
jurisdictional feature or outfall within the project
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Closed Drainage System Inlets - Last Place to Capture Sediment
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Outfall or Sub-Outfall?• Identify the Outfall(s)
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Outfall or Sub-Outfall?• Identify the Outfall(s)
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Outfall or Sub-Outfall?• Identify the Outfall(s)
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Outfall or Sub-Outfall?• Identify the Outfall(s)
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Outfall or Sub-Outfall?• Identify the Outfall(s)
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PROJECT TERMINI
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Sub-Outfall Examples
EPSC Stage 2 of curb inlets
SUB-OUTFALLS
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Sub-Outfall Examples
EPSC Stage 3 of curb inlets SUB-OUTFALLS
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Sub-Outfall Examples
Curb inlet with no inlet protection
SUB-OUTFALL
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Sub-Outfall Examples
Area drain/catch basin protection
SUB-OUTFALL
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Sub-Outfall Examples
Stormwater manholesSUB-OUTFALL
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Sub-Outfall Examples
Stage 2/3 EPSC
Area drain during construction
SUB-OUTFALL
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Sub-Outfall Examples
Stage 3 EPSC
Area drain after construction
SUB-OUTFALL
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Outfalls• Outfalls may change in the EPSC
stages– Existing– Intermediate– Final
• Roadway designer to provide for each EPSC stage:– Outfalls– Respective drainage area– Average slope of drainage area
(Percent slopes)
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Outfall Location(s) - Present (existing) Conditions – Stage 1 EPSC
NATURAL DRAINAGE FEATURE
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PROPOSED SPECIAL & TOE DITCHES
NATURAL DRAINAGE FEATURE FILLED IN
Outfall Location(s) – Proposed Conditions – Stage 2 EPSC
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OUT-#10
Outfall Location(s) – Proposed Conditions – Stage 2 EPSC
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• Toe Ditch or Special Ditch– Formed where fill meets existing
ground– Becomes a “v-ditch”– Steep slope– Concentrated flow– High velocities– Protection needed
• During construction • Post construction
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Outfall Locations
Present (existing)Conditions
Stage 1 EPSC
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Outfall Locations
Proposed Conditions
Stage 2/3 EPSC
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Outfall Locations
Proposed Conditions
Stage 2/3 EPSC
OUT-#13
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Outfall Locations – Stage 1 EPSC (Clearing & Grubbing)
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Outfall Locations – Stage 2 EPSC (Intermediate - Mass Grading)
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Outfall Locations – Stage 3 EPSC (Final Grading)
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Outfall Locations – Stage 1/2
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