bioretention site evaluation and considerations for design

Site Evaluation and Considerations for Design and Review of Bioretention

Jay Dorsey & John MathewsODNR-DSWRApril 16, 2014

Goals for PresentationUnderstanding Why Bioretention Practices

Fail Site Considerations

Right BMP? Site Limitations Site Properties for Design

Giving Bioretention Practices the Best Chance to Function Over the Long Haul

Why Do Bioretention Practices Fail?Undersized Bioretention Cell Based on Overestimate of Infiltration Capacity

Why Do Bioretention Practices Fail?Undersized Bioretention Cell Based on Overestimate of Infiltration Capacity

Sediment Clogging of Geotextile Filter Between Soil and Aggregate Layers

Why Do Bioretention Practices Fail?1. Sediment Clogging of Filter Bed Surface

Clogging of Filter Surface

Source: Bill Hunt, NCSU-BAE

Clogging of Filter Surface

Why Do Bioretention Practices Fail?1. Sediment Clogging of Filter Bed Surface2. Eroding Sideslopes - Unstable Sideslopes

and/or Concentrated Flow

Source: Brad Wardynski, NCSU-BAE

Source: Amy Dutt,Urban Wild

Why Do Bioretention Practices Fail?1. Sediment Clogging of Filter Bed Surface2. Eroding Sideslopes3. Undersized Surface Ponding Volume

Storage Volume


Storage Volume


Severely Undersized (>25%)35%

Results: Storage VolumeNeed to inspect average ponding

depth (not height of outlet structure)


Why Do Bioretention Practices Fail?1. Sediment Clogging of Filter Bed Surface2. Eroding Sideslopes3. Undersized Surface Ponding Volume4. Construction Issues/Lack of Construction

Oversight

Construction Issues/Lack of Construction Oversight

Loss of Exfiltration/Infiltration Capacity smearing or compaction of subgrade soils during

excavation compaction of filter bed soils during construction




Materials – esp. filter sand and planting media

Photo: Geo Growers




Materials – esp. filter sand and planting media Elevations – filter bed surface, overflow




Materials – esp. filter sand and planting media Elevations – filter bed surface, overflow Existing or Hidden Infrastructure




Materials – esp. filter sand and planting media Elevations – filter bed surface, overflow Existing or Hidden Infrastructure Keeping Sediment Out of BRC During

Construction – staging, site drainage and erosion control during construction, site stabilization

Source: Amy Dutt,Urban Wild


Oversight5. Plant Selection and Management

Plant Selection and Management

Poor plant selection based on survivability – extremely droughty, extended ponding, salt

Poor plant selection based on fit for location – aesthetics, safety, maintainability

Inappropriate or inadequate post-construction management

Plant Selection and Management- Resources -

Horticulturalist or Landscape Architect (esp. ones with stormwater background)

Local Rain Garden Alliance (e.g. CincyRain.org)

Rain Garden and Stormwater Plant Guides

Grassed Bioretention

VaDCR

Independence, OH

Orange Village, OH

Landscape Plants vs Grass

Conrad St, Toledo

Landscape Plants vs Grass

Third Federal Bank, North OlmsteadSource: Dan Bogoevski, Ohio EPA

Grassed Bioretention


Oversight5. Plant Selection and Management6. Lack of Maintenance


Oversight5. Plant Selection and Management6. Lack of Maintenance7. Bioretention BMP or Design Poor Fit for

Site

Planning ConsiderationsDrainage Area < 2 Acres Existing Infrastructure Setbacks from Property Lines, Building

Foundations, Wells, Septic Systems

Planning ConsiderationsDrainage Area < 2 Acres Existing Infrastructure Setbacks from Property Lines, Building

Foundations, Wells, Septic Systems

Commitment/Resources to Maintain Practice

Site EvaluationGroundwater Pollution Concerns

Karst or Shallow Sand/Gravel Aquifer Areas

Search on “ODNR groundwater program”

Groundwater Pollution Potential Maps


Karst or Shallow Sand/Gravel Aquifer Areas Shallow Depth to Bedrock Shallow Depth to Water Table

2 ft separation recommended, 1 ft required



2 ft separation recommended, 1 ft required Soil Limitations/Hydrologic Soil Group

(HSG)

Search on “ODNR soils data”

Soil Survey Information

Planning and Design Considerations HSG Shorthand

HSG-A • Shallow aquifer? • Avoid short circuiting from pollutant “hot spots”

HSG-B• Easy to work with• Maintain infiltration capacity of soils• Drainage usually recommended

HSG-C • Oftentimes in optimal landscape position• Maintain infiltration capacity of soils• Drainage required

HSG-D• Must identify limitations and design accordingly• Drainage required



2 ft separation recommended, 1 ft required Soil Infiltration Capacity

P

Qoverflow

ET

S2

F1

P – Precipitation (Rainfall & Snowmelt)

ET – Evaporation & Transpiration

S1 – Temporary Surface Storage

S2 – Temporary Subsurface Storage

S1

F2

Qin

Qin-leak

Qout-leak

Qout

F1 – Infiltration

F2 – Exfiltration

Qin – Runon/Lateral Inflow

Qout - Runoff

Qtile

BMP Hydrology

Infiltration Test for BMP Design?Bore Hole/ Perc Test (v1)?

Ponded RingInfiltrometer Test

3-Dimensional Flow

~1-Dimensional Flow

Single Ring Infiltrometer

Estimating Infiltration Rates for BMPs for Site Planning

Soil Water Characteristics Calculator

Subgrade USDASoil Texture

ClayContent

%

Ksat(in/hr)

Sand < 8 2.8

Loamy Sand < 15 2.0

Sandy Loam < 20 0.80

Loam 7 – 27 0.16

Silt Loam < 27 0.05

Silt < 12 0.05

Sandy Clay Loam 20 – 35 0.07

Clay Loam 27 – 40 0.02

Silty Clay Loam 27 – 40 0.02

Silty Clay 40 – 50 0.01

Sandy Clay 35 – 55 <0.005

Clay > 40 <0.005

Subgrade Kfs Estimates

Pretreatment RealitiesFor the bioretention practice to function:1. The system must remove most sediment

from runoff before it enters the filter bed area The bioretention “system” necessarily includes

pretreatment components2. The runoff must be introduced to the filter

bed area with little or no erosive energy The design must address elevation change

and concentrated flow

Pretreatment Requirements Some form of pretreatment is required

Grass Filter Strip Gravel Verge plus Grass Filter Strip Grass Swale Sediment Forebay


Pretreatment Forebay

Pretreatment

Source: Matt Repasky, ODNR

Grass Filter Strip

Grass Filter Strip and Grass Swale

Sterncrest Road, Orange Village

flow too concentrated, flowpath too short

flow too concentrated, flowpath too short

too steep? add grass filter?

Okay

Much Better Alternative

Good Enough?

Education Center, Zanesville

References ODNR. Rainwater and Land Development Manual. Wardynski and Hunt. 2012. Are Bioretention Cells Being

Installed per Design Standards in North Carolina? A Field Assessment. J. Env. Eng. 138(12): 1210-1217.

Hunt, Davis, and Traver. 2012. Meeting Hydrologic and Water Quality Goals through Targeted BioretentionDesign. J. Env. Eng. 138(6): 698-707.

Brown, Hunt, and Kennedy. 2009. Designing Bioretention with an Internal Water Storage (IWS) Layer. NCSU-CE.

CWP. 2012. West Virginia Stormwater Management and Design Guidance Manual.

Questions:

Jay DorseyWater Resources EngineerODNR, Soil & Water Resources(614) [email protected]

bioretention site evaluation and considerations for design

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