Texas; Innovative Stormwater Controls - Austin Energy

1. Watershed Protection
and Development
Review Department
Environmental Criteria Manual
Updates:
Innovative Stormwater
Controls
Michael Kelly, P.E.
John Gleason, Landscape Architect

2. ECM 1.6.7 Innovative Water Quality
Controls
• Vegetative Filter Strips (VFS)/ VFS –
Disconnection of Imp. Cover
• Biofiltration
• Rainwater Harvesting
• Porous Pavement for Pedestrian Use
• Rain Gardens

3. On-site Stormwater Treatment
Sedimentation/Filtration: standard water quality treatment pond

4. Vegetated Filter Strip/Disconnected
Impervious Cover

5. Vegetative Filter Strips

6. Vegetated Filter Strip Credit/
Disconnected Impervious Cover
1. Same as existing vegetated filter
strip, except allow for smaller
sizing to receive proportionately
reduced credit.
2. Directs water over vegetated area.
3. Requires adequate soil quality &
depth, slope, hydraulic loading
rate.

7. Vegetative Filter
Strips
(acres of VFS per acre
of impervious cover)
Contributing Sand Filtration
Area Imp. Cvr. SOS Equivalency
15% 0.28 NA
25% .45 .40
50% 1.04 .91
75% 1.84 1.61
100% 2.85 2.49

8. Vegetative Filter Strip Design
Allowable in the BSZ
May be natural or engineered
Size: Requires relatively large land
area
Maintain sheet flow
Do not exceed max.
velocities/hydraulic loading rates
Width: as wide as the contributing drainage area
Pavement
Level spreader creates sheet flow
Min. 25’
Length
Vegetated Filter Strip

9. Vegetative Filter Strip Design
Min. 3”
drop
Primary pollutant removal mechanism
Pavement is infiltration
6” min. soil depth
Water depth may not exceed the
height of vegetation
Bunchgrass: min. ht. 18”
Turf: min. ht. 3”

10. Biofiltration
Old Dominion Freight (near Lake Walter Long)

11. Biofiltration
1. Same design procedures as
sedimentation/filtration.
2. Key differences:
1. Addition of organic material into
sand medium.
2. Plants provide key functional
component to remove additional
dissolved nutrients and enhance
aesthetics

12. Biofiltration: Vegetated Flow
Spreader vs. Gabion

13. Diagram of Biofiltration Pond
Cross-Section – Conceptual Design
Sedimentation Filtration Outlet
Inlet
Splitter
Box Separator Element
Outlet Pipe
Filtration Media
Filter Fabric
Vegetation
Gravel
Flood spillway

14. Biofiltration – Landscape Design
• Plants must tolerate wide variations in moisture
• Total Plants: Surface area (s.f.) of pond bottom
x 0.1
• Sedimentation basin: Min. 20% of total plants
• Trees are allowed
• Filtration basin: Min. 50% of total plants
• Min. 20% tall herbaceous
• No more than 30% medium herbaceous
• No trees are allowed

15. Biofiltration Plants - Grasses

16. Biofiltration at TechRidge

17. Rainwater Harvesting
HEB Brodie Lane

18. Rainwater Harvesting: Option A
Captured Runoff discharged to a VFS for infiltration (<72 hr)

19. Rainwater Harvesting
1. Captures runoff to be used for other
beneficial purposes.
2. Capture volume can be sized to meet
watershed specific requirements (e.g.
Urban vs. SOS); requires adequate
infiltration or irrigation field for
ultimate disposal of stormwater
3. May be upsized to provide water
conservation function.

20. Rainwater Harvesting: Option A
Captured Runoff discharged to a VFS for infiltration (<72 hr)

21. Rainwater Harvesting:
Option A

22. Rainwater Harvesting: Option B
Captured Runoff Used to Irrigate Vegetated Area
• Max. 72 hr. drawdown time
• Use retentio/irrigation criteria (ECM 1.6.7A)
• Allowable in the Barton Springs Zone
Conveyance system

23. Rainwater Harvesting: Option B
Captured Runoff Used to Irrigate Vegetated Area
Tank
Sprinkler system (per retention/irrigation criteria)

24. Porous Pavement for Pedestrian Use
Pervious Concrete Permeable Pavers

25. Porous Pavement
1. Retains & infiltrates water underneath
pavement used for pedestrian use
only.
2. Criteria will allow for Impervious Cover
(IC) credit.

26. Porous Pavement
Possibilities include:
• porous concrete
• reinforced turf
• gravel

27. Rain Gardens

28. Rain Gardens
• Filtration or Infiltration system for small
(<1 acre) drainage areas
• Allows for dispersed, small-scale treatment
systems integrated into site landscaping

29. Rain Garden Info: Grow Green

30. Rain Gardens
Plan
Plan View
Section
Section

31. Contact Information
Michael Kelly, P.E. John Gleason
(512) 974-6591 (512) 974-3543
mike.kelly@ci.austin.tx.us john.gleason@ci.austin.tx.us
Environmental Resource Management
Watershed Protection and Development Review Department
505 Barton Springs Road
Austin, Texas 78704