Introduction To The Highway Runoff Manual by moti

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									Introduction To The
Highway Runoff Manual
This introduction focus on:
    • An overview of the Highway Runoff Manual.
    • The definition of Minimum Requirements
    • What is a TDA?
    • BMP (Best Management Practices) selection
       process.
    • More on Runoff Treatment and Flow Control
    • BMP’s covered in StormSHED 3G
Highway Runoff Manual
Chapter 1                        Chapter 4
 Background                      Hydrologic analysis methods


Chapter 2                        Chapter 5
 Planning and design             Permanent BMP selection
  integration into the project    BMP design criteria
  development process.
                                 Chapter 6
Chapter 3                         Construction BMP selection
 Minimum requirements &          ESC, SPCC BMPs
  Applicability                   BMP design criteria
                                  Monitoring guidance
What is a Minimum Requirement

   There are 9 minimum requirements that apply
    when planning and designing a stormwater
    management facility.
   Which MR applies to a project is dependant
    several parameters including: the amount of
    impervious surface added, the presence of
    wetlands, watershed plans, thresholds and
    exceptions.
Activies Exempt From ALL
Minimum Requirements

– Typically Maintenance & Preservation Activities:
 Patching
 Resurfacing without expanding coverage area
 Shoulder grading
 Crack sealing
 Re-shaping/re-grading drainage systems
 Vegetation maintenance
Minimum Requirements 1-4

1 - Stormwater Planning - To demonstrate how water quality
   will be maintained both during project construction and in the
   final developed conditions.
2 - Construction Stormwater Pollution Prevention - To
   ensure that construction projects do not impairwater quality by
   allowing sediment to discharge from the site or allowing spills
   of pollutants.
3 - Source Control – Prevent pollutants from contacting and
   mixing with stormwater. Source control is more cost-effective
   than treatment.
4 - Preservation of Natural Drainage - Preserve natural
   drainage systems to the fullest extent and to prevent erosion.
Activities Subject only to
Minimum Requirement 2


– Repairing roadway base or subgrade
– Some underground utility projects
– Some roadways replacements/removals
 Minimum Requirements 5-9
5 - Runoff Treatment - To reduce pollutant loads and
   concentrations in stormwater.
6 - Flow Control - Prevent increases in the stream channel
   erosion rates; mitigate impacts of prior development and flow
   modifications.
7 - Wetland Protection - To ensure that wetlands receive the
   same level of protection as any other water of the state
8 - Basin/Watershed Planning - To promote the development of
   watershed based resource plans as a means to develop and
   implement comprehensive water resource protection measures
9 - Operations and Maintenance - To achieve appropriate
   preventative maintenance and perform checks to ensure that
   stormwater control facilities are adequately maintained and
   properly operated
Figure 3.1
Figure 3.2
Figure 3.3
What is a TDA?

Threshold Discharge Area - An onsite area
  draining to a single natural discharge location
  or multiple natural discharge locations that
  combine within ¼ mile downstream.

Same a basin, but the area is separated by the
  discharge locations.
Threshold Discharge Area
Figure 4-2a
Threshold Discharge Area
Figure 4-2b
TDA Delineation

Why do we need TDAs?
- consistency in determining flows
- determine Minimum Requirements
- identify outfalls
Best Management Practice (BMP)
Selection

•   Stormwater BMP’s are the physical, structural,
    and managerial practices that when used
    singly or in combination, prevent or reduce the
    detrimental impacts of stormwater, such as the
    pollution of water, degradation of channels,
    damage to structures, and flooding.
Three Distinct Functions of BMP’s

   Source control: Prevents or reduces the
    introduction of pollutants to stormwater
    (Mostly Construction).
   Flow control: Offsets and attenuates the
    increased rate of discharge caused by
    impervious surfaces
   Runoff treatment: Intercepts and reduces the
    physical, chemical, and biological pollutant
    loads generated primarily from highway use
Minimum Requirement 5 –
Runoff Treatment

Unless an exemption applies (see section 3-3.5
of the HRM), any project that adds 5,000
square feet or more of new Polutant Generating
Impervious Surface (PGIS) in a TDA must
provide runoff treatment of stormwater runoff.
The intent is to reduce pollutant loads and
concentrations in stormwater runoff.
Types of Runoff Treatment
Table 3-1

1.   Basic Treatment
2.   Enhanced Treatment
3.   Oil Control*
4.   Phosphorus Control
     Based on: through ADT, ADT at an intersection, and/or if area is
     designated for phosphorus control.

Note EWA oil control requirements and have changed.
Runoff Treatment Criteria
Table 3-4
Runoff
Treatment

Selection
Process
Figure 5-3.2
Minimum Requirement 6
– Flow Control

Unless an exemption applies (see section 3-3.6
of the HRM), any project that adds 5,000
square feet or more of net-new impervious
surfaces in a TDA must provide flow control of
stormwater runoff. The intent is to prevent
cumulative future impacts from increased
stormwater runoff volumes and flow rates on
streams and off WSDOT ROW.
Flow Control Criteria
 Flow
 Control

Selection
Process
Figure 5.3.1
Types of BMP’s Covered in
StormSHED 3G Intermediate Class

Biofiltration – basic runoff treatment
Vegetative Filter Strip – basic runoff treatment
Natural Dispersion – basic and enhanced runoff
  treatment and flow control
Detention Pond – flow control
Infiltration Pond – flow control and (if infiltration
  is within designated parameters) runoff
  treatment.
Bioinfiltration Pond – basic, enhanced, and oil
  runoff treatment and flow control

								
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