construction storm water controls cet-3320 hydrology & hydraulics

Construction Storm Water Construction Storm Water ControlsControls

CET-3320

Hydrology & Hydraulics

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.

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.

Types of Erosion

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.

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

How to Prevent Erosion • Best Way is Using Vegetation on the

Ground

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)

Control Measure Selection Process

1. Identify Problem Area

2. Determine Required Strategy

3. Select Specific Control Measure

Soil Stabilization Measures

- Seeding - Matting

- Sodding -Mulching

- Tree Preservation

- Surface Roughening

Runoff Control Measures

- Check Dams- Slope Drains

- Temporary Dams- Water Bar

Check Dams- Small Rock Dam in

Channel

- Slows Velocity

Temporary Diversion- Directs Runoff from Above Steep

Slopes- Direct Runoff to Sediment Ponds

Slope Drains- Pipe or Chute Placed

on Slope to Convey Surface Runoff Down a Slope Without Causing Erosion

Sediment Control Measures

- Sediment Basin- Sediment Trap/Diversion- Silt Fence- Storm Drain Inlet Protection

Sediment Basin• Temporary Settling Pond

-Slow Release of Runoff

-Allows Sediment to Settle out

-Up to 100 Acres

Sediment Trap/Diversion

Trap:Temporary Settling Pond With Simple Stabilizing Spillway.

Diversion: Detour of Storm Sewer System to Provide an In-Line Sediment Basin.

Silt Fence- Fences Catch Sediment of

Shallow Flow that can’t be Trapped by Other Means.

Storm Drain Inlet Protection- Prevents Sediment

From Entering Storm Sewer System

Some Agencies Have Established Minimum

Standards

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.

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”.

BMP- Permanent Ponds

• Several stages allow water time to slow and pollutants to settle out.

BMP – Open Channels

• Detains first flush allowing settling and groundwater recharge.

BMP- Filter System

• Allows for direct groundwater recharge and filtering of sediments and pollutants.

BMP – Infiltration Trench

• Trenches allow recharge of groundwater and use the ground and media to filter sediment and pollutants.

BMP – Commercially Available Solutions

Manufactured units are available to filter runoff before it leaves the site!

• Filters• Baffles• Separation

Units

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.