construction storm water controls cet-3320 hydrology & hydraulics
TRANSCRIPT
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Construction Storm Water Construction Storm Water ControlsControls
CET-3320
Hydrology & Hydraulics
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EPA Phase 2 Clean Water ActRegulations Require:
• Construction Sites 1 Acre or Larger
• Must not be Allowed to Erode Freely
• Measures Must be Taken to Prevent Erosion & Sediment from Leaving Construction Sites.
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Erosion: Removal & Loss of soil by the
Action of Water (and ice, gravity, & wind)
Sedimentation: Settling Out of Soil Particles
Which are Transported by Water.
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Types of Erosion
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What Must Be Done?
The Owner must:
• Submit a Notice of Intent (NOI) for Construction Activities
• Have Erosion & Sediment Control (E&SC) Plans Developed.
• Must Have a Written Storm Water Pollution Prevention Plan (SWPPP)
• Must Ensure that the Controls are Put in Place and Maintained.
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What Goes in the SWPPP?• Site Information
- Type of Improvements
- Construction Activity Descriptions
- Existing Site Conditions
- Disturbed Area & Weighted C’s
• Description of all Construction E & SC Methods
• Description of Permanent E & SC Methods
• Description of E & SC Maintenance
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How to Prevent Erosion • Best Way is Using Vegetation on the
Ground
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Construction Planning & Controls
Goals
- Disturb as Little as Possible
- Cover (with vegetation) Anything Disturbed for Long Term. (Stabilization)
- Slow Water Down (Runoff Control)
- Catch Anything that does Erode Before it Gets Away. (Sediment Control)
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Control Measure Selection Process
1. Identify Problem Area
2. Determine Required Strategy
3. Select Specific Control Measure
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Soil Stabilization Measures
- Seeding - Matting
- Sodding -Mulching
- Tree Preservation
- Surface Roughening
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Runoff Control Measures
- Check Dams- Slope Drains
- Temporary Dams- Water Bar
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Check Dams- Small Rock Dam in
Channel
- Slows Velocity
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Temporary Diversion- Directs Runoff from Above Steep
Slopes- Direct Runoff to Sediment Ponds
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Slope Drains- Pipe or Chute Placed
on Slope to Convey Surface Runoff Down a Slope Without Causing Erosion
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Sediment Control Measures
- Sediment Basin- Sediment Trap/Diversion- Silt Fence- Storm Drain Inlet Protection
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Sediment Basin• Temporary Settling Pond
-Slow Release of Runoff
-Allows Sediment to Settle out
-Up to 100 Acres
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Sediment Trap/Diversion
Trap:Temporary Settling Pond With Simple Stabilizing Spillway.
Diversion: Detour of Storm Sewer System to Provide an In-Line Sediment Basin.
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Silt Fence- Fences Catch Sediment of
Shallow Flow that can’t be Trapped by Other Means.
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Storm Drain Inlet Protection- Prevents Sediment
From Entering Storm Sewer System
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Some Agencies Have Established Minimum
Standards
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Maintenance
• Measures must be Inspected– Every 7 days– Within 24 hours of a 0.5” rainfall
• Measures must be cleaned out at specific levels and repaired if damaged.
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Watershed Management
• Local agencies are also charged with the management of watersheds within their districts.
• The use of permanent pollutions prevention controls are now being designed into new sites and retrofit into existing ones.
• These Best Management Practices (BMP’s) are required prior to plan approval.
• Usually required to hold a “First Flush” of polluted storm water for “treatment”.
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BMP- Permanent Ponds
• Several stages allow water time to slow and pollutants to settle out.
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BMP – Open Channels
• Detains first flush allowing settling and groundwater recharge.
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BMP- Filter System
• Allows for direct groundwater recharge and filtering of sediments and pollutants.
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BMP – Infiltration Trench
• Trenches allow recharge of groundwater and use the ground and media to filter sediment and pollutants.
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BMP – Commercially Available Solutions
Manufactured units are available to filter runoff before it leaves the site!
• Filters• Baffles• Separation
Units
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Erosion & Sediment Control Protects the Environment
• Keeps Valuable Topsoil in Place
• Keeps Natural Watercourses Free Flowing and Clean
• Keeps pollutants from destroying ecologies and habitats in watersheds.