South OC Interim Hydromod Tool Training

South Orange County Interim Hydromodification Control BMP H dromodification Sizing Tool Training g g

Lisa Austin [email protected] Judd Goodman [email protected] November 17, 20101

1. Introduction

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What is geomorphology?Geomorphology = the scientific study of landforms and thep processes that shape them p

Fluvial = of, relating to, or occurring in a river or stream Geomorphic Impact = Changes in landforms and theprocesses that shape them. Often caused by land use change.

Restoration vs. Hydromodification Managementprevent a future geomorphic impact

fix an existing geomorphic impact

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Why care about hydromodification?Example of geomorphic impact:flow flow flow flow

140140-ft 300300-ft

PrePre-DevelopmentImagesfromGoogleEarth

PostPost-Development4

How is hydromodification managed?Flow Duration Control 101

Di ischarge

PostPost-Urban PrePre-Urban Qc Time

State of the practice for hydromodification control is p y flow duration matching. matching.

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How is hydromodification managed?Flow Duration Control 1011010-year

10% of 2-year 2-y

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How is hydromodification managed?Flow Duration Control 101On Site Regional In-Stream

Non-Structural

Minimize impervious areas

Prioritize low-infiltrating soils for development and high infiltrating soils for recharge and flow management

Riparian buffers Design for sediment passthrough from open spaces

Structural

Distributed BMPs providing volume and/or fl d/ flow reduction d ti through one or more of the following mechanisms: Infiltration Evapotranspiration Rainwater harvesting Biotreatment w/outlet control

Regional detention / infiltration R i l d t ti i filt ti basins (designed for flow duration control, or for detention and volume reduction through alternatives such as storage and use or discharge to nonsusceptible water bodies)

Grade control structures Drop structures Bed and bank reinforcement

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How is hydromodification managed?Flow Duration Control 101Route post-project runoff through flow duration control facilities to mimic pre-development hydrology.

LID : Bioretention

Regional: Detention Basin

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Development Project ProjectionsMunicipality QUESTIONS 1. What types of new development and redevelopment projects are anticipated which may need to use the interim hydromodification sizing tool? Mission Viejo Laguna Niguel Dana Point Lake Forest San Juan Capistrano

Commercial

High Density Residential

Small Redevelopment

Residential, Commercial, Sports Park, & Playgrounds

Redevelopment

2. What is the range of project sizes that are j t i th t anticipated in the next year or so?

0.5 to 10 3 0 5 t 10.3 acres

2 acres

< 1 to 2.3 acres

60 to < 800 t acres

1 to < 50 acres

3. What two types of structural BMPs would be most useful to have a design tool for?

Underground Detention Vault & Bioretention

Bioretention

Under-ground Detention Vault & Bioretention

Detention Pond, Detention Vault, Detention Pipe, & Bioretention

Detention Vault, , Detention Pipe, Bioretention, Detention Domes, & Combined Bioretention and Vault lt

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Bioretention Facility

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Underground Vault ProductsCONTECH CMP Systems CONTECH CON/SPAN CONTECH CON/STORM

CUDO Water St W t Storage System S t

StormTech Chambers

StormTrap Detention

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Explanation of the Interim Hydromodification Criteria (IHC)

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Applicability ScreeningIF the project discharges storm water runoff into: th j t di h t t ff i t a. underground storm drains that discharge directly to bays or the ocean, OR b. conveyance channels whose bed and banks are concrete lined all the way from the point of discharge to ocean waters, enclosed bays, estuaries, di h t t l db t i or water storage reservoirs and lakes THEN, the interim hydromodification criteria do not apply. IF NOT, THEN proceed to Interim Hydromodification Criteria

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Interim Hydromodification Criteria (IHC)The project shall implement the following criteria by comparing the pre-development (naturally occurring) preand post-project flow rates and durations using a postcontinuous simulation hydrologic model: For flow rates between 0.1Q2 and Q5: postpost-project flows shall not exceed pre-development pre( (naturally occurring) p y g) peak flows. For flow rates between Q5 and Q10: 10: postpost-project peak flows may exceed prepredevelopment (naturally occurring) flows by up to 10% for a 1-year frequency interval 1interval.14

Objective of the Sizing Tool

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Sizing Tool ObjectiveTo allow project proponents to easily determine the necessary BMP storage volume and footprint area for flow duration control per the South Orange County IHC. South OC Copermittee Project Proponent Consultant

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2. BMPs Modeled

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BMPs and Conditions ModeledBioretention A/B soils assumes infiltration C/D soils assume underdrain w/ low flow orifice il d d i /l fl ifi Underground Vault A/B soils assumes infiltration C/D soils assumes low flow orifice Fixed BMP depth & adjusted footprint area until IHC p j p is met.

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Bioretention

Slotted Underdrain only for C/D Soils19

Bioretention

C/D Soils only20

Underground Vault

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Underground Vault

C/D Soils only22

3. Sizing Tool Inputs

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InputsINPUTS

BMP Type Catchment 85th Percentile Catchment Soil Type Imperviousness (Bioretention Area Storm Depth ID (A/B or C/D) (%) or Vault) (acres) (inches)

Catchment ID is a label that helps to organize different drainage areas within a Priority Development Project.The user can choose any naming convention they wish for the Catchment ID.

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InputsINPUTS


BMP Type must be entered as either Bioretention or Vault.These are the only BMP types which have been modeled to meet the IHC at this time.

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InputsINPUTS


Soil Type must be entered as A/B if the catchment is a Type A or B soil or C/D if the C/D catchment is a Type C or D soil.Site specific study to determine Hydrologic Soil Group is preferred. Hydrologic Soil Group for a site can be found at http://websoilsurvey.nrcs.usda.gov/app/websoilsurvey.aspx26

Soil TypeHydrologic H d l i Soil Group A B C D Proportion of South P ti f S th OC 3% 13% 37% 47%

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InputsINPUTS


Catchment Area is the acreage tributary to the BMP being sized sized.For Bioretention, the catchment area must include the area of the BMP itself. it lf This is not the case for the Underground Vault because precipitation does not land directly on it it.28

InputsINPUTS


Imperviousness is the cumulative proportion of impervious surface area in the project catchment.All impervious cover is assumed to be directly connected to the storm drain system. This includes, but is not limited to, rooftops, asphalt pavement, and concrete surfaces. For bioretention, the BMP footprint area should be assumed to be impervious impervious.

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InputsINPUTS


85th Percentile Storm Depth is used to compute the LID Capture Volume per the Orange County Drainage Area Management Plan Technical Guidance Document.

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85th Percentile Storm Depth

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4. Sizing Tool Outputs

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OutputsOUTPUTS O S BMP Footprint Area (square feet) BMP Capture Volume (cubic feet) Total Hydromod Capture Orifice Diameter BMP Volume Volume > LID Capture (inches) (cubic feet) Volume?

BMP Footprint Area is the area, in square feet, of the BMP at the overflow weir crest crest.

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BMP Footprint Area

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OutputsOUTPUTS O S BMP Footprint Area (square feet) BMP Capture Volume (cubic feet) Total Hydromod Capture Orifice Diameter BMP Volume Volume > LID Capture (inches) (cubic feet) Volume?

BMP Capture Volume is the storage capacity, in cubic feet, of the BMP below the overflow weir crest. crest

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BMP Capture VolumeIncludes storage capacity in it i media

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OutputsOUTPUTS BMP Footprint Area (square feet) BMP Capture Volume (cubic feet) Total Hydromod Capture Orifice Diameter O ifi Di t BMP Volume Volume > LID Capture (inches) (cubic feet) Volume?

Total BMP Volume is the storage capacity, in cubic feet, below the suggested freeboard , gg elevation.

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Total BMP VolumeIncludes storage capacity in media

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Orifice Diameter is the size of the low flow control opening, in inches. p gThe diameter is rounded to the nearest 1/32nd inch, so that standard drill bits can be used to create the orifice.

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The last output provides a yes or no answer to the question, Is the Hydromodification Capture Volume greater than the LID Capture Volume?If the answer is yes, then the hydromodification BMP sizing outputs yes are appropriate. If the answer is no then the LID Capture Volume should be used in place of the Hydromodification BMP Capture Volume.

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LID vs. Hydromod Capture Volume

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5. Sizing Chart / Nomograph

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Footprint Area

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Capture Volume

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Total Volume

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BREAK

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6. Example Calculation

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Catchment Delineation

= Catchments

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1

2

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InputsINPUTS BMP Type Catchment 85th Percentile Catchment Soil Type Imperviousness (Bioretention Area Storm Depth ID (A/B or C/D) (%) or Vault) ) ( (acres) ) ( (inches) ) 1 Bioretention C/D 2 65 1.05

1

Vault

C/D

2

65

1.05

Let s Lets try the Spreadsheet Tool

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OutputsOUTPUTS Total Orifice Hydromod Capture BMP Footprint BMP Capture Volume BMP Volume Diameter Volume > LID Capture Area (square feet) ( bi feet) ( bi feet) (i h ) ( f ) (cubic f ) (cubic f ) (inches) Volume? l ?

Bioretention

4,462

10,088

12,472

1 5/16

YES

Vault

2,044 2 044

14,308 14 308

16,352 16 352

1 9/32

YES

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7. Alternative Configurations

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BMP Modification Criteria1. The footprint area at the bottom of the BMP shall be h f t i t t th b tt f th h ll b equal to or greater than the bottom footprint calculated using the sizing tool. g gOUTPUTS BMP Footprint BMP Capture Total Orifice Hydromod Capture adjust to Area Volume BMP Volume Diameter Volume > LID Capture get bottom (square feet) (cubic feet) (cubic feet) (inches) Volume?

footprint Bioretention4,462 10,088 12,472 1 5/16 YES

Vault

2,044

14,308

16,352

1 9/32

YES

vertical walls52

Bioretention Bottom Footprint AreaExample:If footprint @ weir crest = 50 x 100, Then, Then width @ bottom = 50 2(1.5*3) = 41 Length @ bottom = 100 2(1.5*3) = 91 Bottom Footprint Area = 41 91 41 x 91 = 3,731 sq ft

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BMP Modification Criteria2. h 2 The BMP Capture Volume stored below the C t l t db l th overflow weir crest shall be equal to or greater than the capture volume calculated using the sizing p g g tool.OUTPUTS BMP Footprint BMP Capture Total Orifice Hydromod Capture Area Volume BMP Volume Diameter Volume > LID Capture (square feet) (cubic feet) (cubic feet) (inches) Volume?

4,462

10,088

12,472

1 5/16

YES

2,044

14,308

16,352

1 9/32

YES

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BMP Modification Criteria3. h 3 The available freeboard height and storage above il bl f b d h i ht d t b the overflow weir crest can be modified as long as the peak design discharge, can be p p y p g g , properly conveyed. Qpeak : Based on OC Local Drainage Manual and Hydrology Manual OR local permitting authority. e.g. Q = 0.90 (I-Fm) A 0 90 (I F Hydraulics: Use weir equation or other appropriate method. e.g. Q = 3.33 L H1.5 Q = 3.33 (L - 0.2H) H1.5 [suppressed] [contracted]55

Vault Modification ExampleIf the design depth is reduced from 7 feet to 4 feet, then the feet footprint area must increase to maintain the BMP Capture Volume. For this case the footprint must increase by at least 7/4 ( (1.75) times assuming the walls are vertical. Increasing the design ) g g g depth from 7 feet in order to reduce the footprint, however, is not an allowable modification.

decrease depth from 7 to 4 increase footprint area by 7/4 times

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8. Design Guidance

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Technical Guidance SourcesCASQA New Development and Redevelopment Handbook http://www.cabmphandbooks.com/development.asp Orange County DRAFT Technical Guidance Document for Project Water Quality Management (WQMPs) Los Angeles County Dept. of Public Works LID Manual http://dpw.lacounty.gov/wmd/dsp_LowImpactDevelopment.cfm Ventura County Technical Guidance Manual for Stormwater Quality Control Measures http://www.vcstormwater.org/technicalguidancemanual.html

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9. Wrap Up

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Documents

South OC Interim Hydromod Tool Training