This document discusses reasons why bioretention practices fail and considerations for proper site evaluation and design. The top reasons for failure are sediment clogging, undersized cells due to overestimated infiltration, eroding sideslopes, and undersized ponding volumes. Other major causes are construction issues, poor plant selection and maintenance, and lack of pre-treatment. Proper site evaluation considers soil type, depth to bedrock/water table, and drainage area. Pretreatment is required to remove sediment before it reaches the bioretention cell.

1. Site Evaluation and
Considerations for Design
and Review of Bioretention
Jay Dorsey & John Mathews
ODNR-DSWR
April 16, 2014

2. Goals for Presentation
 Understanding 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

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

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

5. Why Do Bioretention Practices Fail?
Undersized Bioretention Cell Based on
Overestimate of Infiltration Capacity
Sediment Clogging of Geotextile Filter
Between Soil and Aggregate Layers

6. Why Do Bioretention Practices Fail?
Undersized Bioretention Cell Based on
Overestimate of Infiltration Capacity
Sediment Clogging of Geotextile Filter
Between Soil and Aggregate Layers

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

8. Clogging of Filter Surface

9. Source: Bill Hunt, NCSU-BAE
Clogging of Filter Surface

10. Source: Bill Hunt, NCSU-BAE

11. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes - Unstable Sideslopes
and/or Concentrated Flow

12. Source: Brad Wardynski, NCSU-BAE
Source: Amy Dutt,
Urban Wild

13. Source: Brad Wardynski, NCSU-BAE

15. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes
3. Undersized Surface Ponding Volume

16. Storage Volume
Source: Brad Wardynski, NCSU-BAE

17. Storage Volume
Source: Brad Wardynski, NCSU-BAE
Severely Undersized (>25%)
35%

18. Results: Storage Volume
Need to inspect average ponding
depth (not height of outlet structure)
Source: Brad Wardynski, NCSU-BAE

20. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes
3. Undersized Surface Ponding Volume
4. Construction Issues/Lack of Construction
Oversight

21. 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

26. 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

29. Photo: Geo Growers

34. 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
 Elevations – filter bed surface, overflow

36. 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
 Elevations – filter bed surface, overflow
 Existing or Hidden Infrastructure

38. 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
 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

41. Source: Amy Dutt,
Urban Wild

42. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes
3. Undersized Surface Ponding Volume
4. Construction Issues/Lack of Construction
Oversight
5. Plant Selection and Management

43. 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

44. 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

45. Grassed
Bioretention
VaDCR
Independence, OH
Orange Village, OH

46. Landscape Plants vs Grass
Conrad St, Toledo

47. Landscape Plants vs Grass

48. Landscape Plants vs Grass

49. Third Federal Bank, North Olmstead
Source: Dan Bogoevski, Ohio EPA
Grassed Bioretention

50. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes
3. Undersized Surface Ponding Volume
4. Construction Issues/Lack of Construction
Oversight
5. Plant Selection and Management
6. Lack of Maintenance

51. Why Do Bioretention Practices Fail?
1. Sediment Clogging of Filter Bed Surface
2. Eroding Sideslopes
3. Undersized Surface Ponding Volume
4. Construction Issues/Lack of Construction
Oversight
5. Plant Selection and Management
6. Lack of Maintenance
7. Bioretention BMP or Design Poor Fit for
Site

53. Planning Considerations
 Drainage Area < 2 Acres
 Existing Infrastructure
 Setbacks from Property Lines, Building
Foundations, Wells, Septic Systems

54. Planning Considerations
 Drainage Area < 2 Acres
 Existing Infrastructure
 Setbacks from Property Lines, Building
Foundations, Wells, Septic Systems
 Commitment/Resources to Maintain Practice

55. Site Evaluation
 Groundwater Pollution Concerns
 Karst or Shallow Sand/Gravel Aquifer Areas

56. Search on “ODNR groundwater program”
Groundwater Pollution Potential Maps

57. Site Evaluation
 Groundwater Pollution Concerns
 Karst or Shallow Sand/Gravel Aquifer Areas
 Shallow Depth to Bedrock
 Shallow Depth to Water Table
 2 ft separation recommended, 1 ft required

58. Site Evaluation
 Groundwater Pollution Concerns
 Karst or Shallow Sand/Gravel Aquifer Areas
 Shallow Depth to Bedrock
 Shallow Depth to Water Table
 2 ft separation recommended, 1 ft required
 Soil Limitations/Hydrologic Soil Group
(HSG)

59. Search on “ODNR soils data”
Soil Survey Information

60. 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

61. Site Evaluation
 Groundwater Pollution Concerns
 Karst or Shallow Sand/Gravel Aquifer Areas
 Shallow Depth to Bedrock
 Shallow Depth to Water Table
 2 ft separation recommended, 1 ft required
 Soil Infiltration Capacity

62. 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

63. Infiltration Test for BMP Design?
Bore Hole/
Perc Test (v1)?
Ponded Ring
Infiltrometer Test
3-Dimensional
Flow
~1-Dimensional
Flow

64. Single Ring Infiltrometer

65. Single Ring Infiltrometer

66. Estimating Infiltration Rates for
BMPs for Site Planning

67. Soil Water Characteristics Calculator

68. Subgrade USDA
Soil Texture
Clay
Content
%
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

71. Pretreatment Realities
For 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 components
2. 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

72. Pretreatment Requirements
 Some form of pretreatment is required
 Grass Filter Strip
 Gravel Verge plus Grass Filter Strip
 Grass Swale
 Sediment Forebay

73. Source: Brad Wardynski, NCSU-BAE
Pretreatment Forebay

74. Pretreatment

75. Source: Bill Hunt, NCSU-BAE

76. Source: Matt Repasky, ODNR
Grass Filter Strip

77. Grass Filter Strip and Grass Swale
Sterncrest Road, Orange Village

78. flow too concentrated,
flowpath too short

79. flow too concentrated,
flowpath too short
too steep?
add grass filter?

80. Okay

81. Okay
Much Better
Alternative

82. Good
Enough?

84. Education Center, Zanesville

85. 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 Bioretention
Design. 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.

86. Questions:
Jay Dorsey
Water Resources Engineer
ODNR, Soil & Water Resources
(614) 265-6647
jay.dorsey@dnr.state.oh.us