IBS Site Drainage: Senior Design Project IBS Site Drainage: Senior - - PowerPoint PPT Presentation

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IBS Site Drainage: Senior Design Project IBS Site Drainage: Senior - - PowerPoint PPT Presentation

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IBS Site Drainage: Senior Design Project IBS Site Drainage: Senior Design Project Len Wright, Ph.D., PE Len Wright, Ph.D., PE Lecturer, CEAE Lecturer, CEAE Wright.Len@gmail.com Wright.Len@gmail.com September 11, 2008 September 11, 2008

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IBS Site Drainage: Senior Design Project IBS Site Drainage: Senior Design Project

Len Wright, Ph.D., PE Len Wright, Ph.D., PE Lecturer, CEAE Lecturer, CEAE Wright.Len@gmail.com Wright.Len@gmail.com September 11, 2008 September 11, 2008

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OUTLINE OUTLINE

  • Motivation for Stormwater Management

Motivation for Stormwater Management

  • Quantity (both onsite, local, and watershed)

Quantity (both onsite, local, and watershed)

  • Quality (receiving waters)

Quality (receiving waters)

  • City of Boulder Stormwater Standards

City of Boulder Stormwater Standards

  • Suggested analytical methods to quantity

Suggested analytical methods to quantity-

  • based

based design standards design standards

  • LEED standards

LEED standards

  • Suggested analytical methods to meet LEED

Suggested analytical methods to meet LEED requirements requirements

  • State of the practice in sustainable drainage:

State of the practice in sustainable drainage: concepts and examples concepts and examples

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Motivation for Management of Quantity Motivation for Management of Quantity as well as Quality as well as Quality

  • Relief of local flooding drove traditional

Relief of local flooding drove traditional drainage system design. drainage system design.

  • Impervious surfaces combined with

Impervious surfaces combined with conveyance systems increase runoff volumes conveyance systems increase runoff volumes and peak flow rates downstream. and peak flow rates downstream.

  • Downstream flooding concerns drove designs

Downstream flooding concerns drove designs to include detention facilities. to include detention facilities.

  • Awareness of the impacts of NPS pollution to

Awareness of the impacts of NPS pollution to receiving waters. receiving waters.

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“ “Good Drainage Good Drainage” ”

Roadways, Paved Surfaces and Turf Roadways, Paved Surfaces and Turf Used to Collect, Convey and Used to Collect, Convey and Concentrate Runoff Concentrate Runoff

The the objective conventional site The the objective conventional site design is to increase runoff. design is to increase runoff.

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Idealized Impacts of Development Idealized Impacts of Development

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City of Boulder Stormwater Standards City of Boulder Stormwater Standards

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Suggested Analytical Methods to Satisfy Suggested Analytical Methods to Satisfy Flow Rate Requirements Flow Rate Requirements

Rational Method for areas less than 160 acres (page 7-15 Boulder Design Standards).

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Rational Method Rational Method

  • Q = CiA

Q = CiA

  • C is a function of land cover, soils

C is a function of land cover, soils

  • i is the rainfall intensity (inches/hour) for a

i is the rainfall intensity (inches/hour) for a specified time of concentration specified time of concentration

  • A is the total area in acres contributing

A is the total area in acres contributing runoff. runoff.

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City of Boulder IDF Curves City of Boulder IDF Curves

  • Based on UDFCD

Based on UDFCD rainfall analysis rainfall analysis

  • Ordinates are Rainfall

Ordinates are Rainfall Intensities (in/hr) Intensities (in/hr)

  • P. 7
  • P. 7-
  • 17 of Boulder

17 of Boulder’ ’s s Design Standards Design Standards

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City of Boulder Detention Requirements City of Boulder Detention Requirements

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Runoff Volume considerations muddy the waters! For basins under 160 acres, use triangular or trapezoidal Unit hydrograph, or FAA method outlined in UDFCD vol. 2.

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LEED Design Criteria LEED Design Criteria

  • 6.1 Quantity Control: Post development

6.1 Quantity Control: Post development peak *AND* volume must not exceed peak *AND* volume must not exceed predevelopment levels for 1 and 2 year 24 predevelopment levels for 1 and 2 year 24 hour runoff. hour runoff.

  • 6.2 Quality Control: 90% of Average

6.2 Quality Control: 90% of Average Annual Annual RAINFALL RAINFALL (NOT runoff based!). (NOT runoff based!).

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Idealized Urban Runoff Hydrograph Idealized Urban Runoff Hydrograph

TIME DISCHARGE

Post-development hydrograph Post-development with detention Pre-development hydrograph

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Analytical Methods to Satisfy both LEED Analytical Methods to Satisfy both LEED and Boulder and Boulder’ ’s Detention Requirements s Detention Requirements

  • Must estimate pre and post development

Must estimate pre and post development volumes as well as peaks volumes as well as peaks

  • Rational formula is peak flow only.

Rational formula is peak flow only.

  • Simplified hydrograph analysis is required

Simplified hydrograph analysis is required (ie NOT just rational method). (ie NOT just rational method).

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Trapezoidal Synthetic Unit Hydrograph Trapezoidal Synthetic Unit Hydrograph

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where: tc = time of concentration. Q = Flow at time t, in cfs. Qp = Peak flow. r = falling limb coefficient sd = storm duration

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UDFCD Methods Suggested by City of UDFCD Methods Suggested by City of Boulder: FAA Method Boulder: FAA Method

  • UDFCD.org

UDFCD.org “ “Downloads Downloads” ” “ “Technical Technical Downloads Downloads” ”

  • FAA

FAA

  • Rainfall analysis

Rainfall analysis

  • UDFCD

UDFCD

  • NOAA IDF maps

NOAA IDF maps

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Analytic Methods for Estimating Storm Analytic Methods for Estimating Storm Volumes Volumes

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1. 1.

Use NOAA Atlas 2 Volume 3 maps as input to Use NOAA Atlas 2 Volume 3 maps as input to “ “UD UD-

  • Rainzone.xls

Rainzone.xls” ”

2. 2.

Use UDFCD Use UDFCD “ “UD UD-

  • Rainzone.xls

Rainzone.xls” ” to estimate the 1 to estimate the 1 hour rainfall depth for the designed frequency. hour rainfall depth for the designed frequency.

3. 3.

Use the 1 hour precipitation values as input to the Use the 1 hour precipitation values as input to the UDFCD UDFCD “ “UD UD-

  • Detention

Detention” ” spreadsheet to estimate spreadsheet to estimate the storage volume and release rate the storage volume and release rate requirements. requirements.

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NOAA Atlas 2, Volume 3 (Colorado) from NOAA Atlas 2, Volume 3 (Colorado) from http://hdsc.nws.noaa.gov http://hdsc.nws.noaa.gov

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Output of the FAA UDFCD Spreadsheet Output of the FAA UDFCD Spreadsheet Analysis Analysis

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LEED Points: Water Efficiency LEED Points: Water Efficiency

  • Credit 1.1, Water Efficient landscaping

Credit 1.1, Water Efficient landscaping -

  • 1

1 point point

  • Credit 1.2, Water Efficient Landscaping

Credit 1.2, Water Efficient Landscaping -

  • 1

1 point point

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Sustainable Drainage Design Low Sustainable Drainage Design Low-

  • Impact Development (LID)

Impact Development (LID)

  • Traditional urban drainage designs are based on

Traditional urban drainage designs are based on large, rare events, with return frequencies from 2 large, rare events, with return frequencies from 2 to 100 years. These are termed major (10 to 100 years. These are termed major (10-

  • 100 yr)

100 yr) and minor (2 and minor (2-

  • 10yr) events.

10yr) events.

  • 95% of rain events have a return period less than

95% of rain events have a return period less than 2 years for Denver, CO. This is reflected in the 2 years for Denver, CO. This is reflected in the LEED Water Quality requirement 6.2 to LEED Water Quality requirement 6.2 to “ “capture capture and treat and treat” ” 90% of the average annual rainfall. 90% of the average annual rainfall.

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Sustainable Drainage Concepts Sustainable Drainage Concepts – – A Sea A Sea

  • f Acronyms!
  • f Acronyms!
  • BMP :

BMP : “ “Best Best” ” Management Practices. Management Practices.

  • SUDS: UK term,

SUDS: UK term, “ “Sustainable Urban Sustainable Urban Drainage Systems Drainage Systems” ”. .

  • LID: Low Impact Development. Over

LID: Low Impact Development. Over-

  • arching design philosophy to minimize the

arching design philosophy to minimize the hydrologic impact of development. hydrologic impact of development.

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Conventional Pipe and Pond Centralized Control

“ “Efficiency Efficiency” ”

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Distributed Small-scale Controls

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Curb Street Storm Drain High Rate Biofilter Side Walk Tree Inlet Tree Box Filter

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Existing Ground 2’ 2” Mulch Drain Pipe

Filtration System Filtration System Bioretention in a Box

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Lot Detail Lot Detail

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Side View of Bioretention Area Side View of Bioretention Area

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Environmental Center of the Rockies, Environmental Center of the Rockies, Boulder Colorado Boulder Colorado

  • One of 25 demonstration projects funded by

One of 25 demonstration projects funded by the National Geographic Society, The the National Geographic Society, The Conservation Fund, and the USGS Conservation Fund, and the USGS

  • Designed by Bill Wenk and Joan Woodward

Designed by Bill Wenk and Joan Woodward

  • Studied by Wright Water Engineers and the

Studied by Wright Water Engineers and the University of Colorado University of Colorado

  • Designed to contain the 3 yr runoff event

Designed to contain the 3 yr runoff event

  • nsite
  • nsite
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Site Scale Experience Site Scale Experience

  • Use of water on

Use of water on-

  • site

site has real value has real value

  • Micro climate is an

Micro climate is an essential component essential component

  • Hardscape storage

Hardscape storage was expensive was expensive

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