1. CITY OF HOUSTON FLOODING & DRAINAGE COMMITTEE PUBLIC WORKS AND ENGINEERING May 18, 2010

2. General Topics  Low Impact Development Techniques (LID)  Cottage Grove Pilot Study Abbreviations  IDM – Infrastructure Design Manual  LID – Low Impact Development  TCEQ – Texas Commission on Environmental Quality  BMP – Best Management Practice

3. Chapter 13 – IDM Stormwater Quality Design  Information for use of Low Impact Development (LID) techniques for stormwater quality/quantity applications  Include: Bioretention, Infiltration Trenches, Porous Pavement, Vegetative Swales, Green Roofs, Hard Roofs, Rain Barrels

4. Bioretention Basin

5.  Using in-situ or new soils, bioretention area to empty within 48 hours.  Accomplished through infiltration, evapotranspiration, and/or a subsurface drainage system.  Mitigating detention volume can be reduced by volume in the bioretention area below maximum design water surface.

6. Porous/Pervious Concrete

7.  Pavement surface may either be soft (grass) or hard (concrete, asphalt)  Underlying permeable layer serves as a storage reservoir for runoff and/or infiltration.  Porous Pavement is applicable for water quality and water quantity control practices.  Limited to lightly traveled surfaces (i.e. parking pads in parking lots, trails and sidewalks).  Porous pavement is not permitted for residential driveways (area of pavement likely to be coated or paved over because of a lack of awareness) commercial areas designed for heavy traffic volume and/or vehicles.

8. Porous/Permeable Pavement Installations  Rice University Campus – sidewalks  Rice University Parking Lot – Combination of porous pavement and BioSwales  Cliff Tuttle Park – Permeable Pavers

9. Infiltration Trenches  Trenches or basins that temporarily detain a design water quality volume while allowing infiltration to occur over a prescribed period of time.  Trenches are applicable for both water quality and water quantity control practices.  Design driven by ability of soils to drain  Subsurface drainage systems are required where the in- situ subsoil rate doesn’t work or project is constructed on fill soils.  Mitigating detention volume can be reduced by the amount of infiltration into the subsoil and the volume of voids within the trench area.

10. Dry Swale

11. Dry Swales  Flow depth should be less than 4 inches for water quality treatment.  Flow velocity should be less than 1 fps for water quality (non-erosive velocities for grass and soils).  Length should yield a 10 minute residence time.  Side slopes should be flatter than 3:1.  Maximum ponding time should be <48 hours.  Mow dry swales as required during growing season to maintain grass heights in the 4 to 6 inch range.

12. Dry/Bio Swales Installations  Rice University Parking Lot  Kendall Library Parking Lot  Federal Reserve Bank Building  MFAH – Bayou Bend  Hermann Park Plaza

13. Wet Swale

14. Wet Swales  Flow depth should be less than 4 inches for water quality treatment.  Flow velocity should be less than 1 fps for water quality (non-erosive velocities for grass and soils).  Length should yield a 10 minute residence time.  Side slopes should be flatter than 3:1.  Maximum ponding time should be < 48 hours.  Wet swales, employing wetland vegetation or other low maintenance ground cover do not require frequent mowing.

15. Rain Barrel

16. Rain Barrels  Gutters and downspouts carry water from the rooftops to rain barrels  Rain barrels should be equipped with a drain spigot.  Overflow outlet must be provided to bypass rain barrel from large rainfall events.  Rain barrel must be designed with removable, child resistant covers and mosquito screening.  Empty rain barrel after each rainfall event.  Rain barrel should be inspected annually  Installations: Hospitality Apartments

17. Hard Roofs/Green Roofs Hard Roofs  Detention volume can be controlled in several ways,  Typically, simple drain ring is placed around roof drains.  Flow into the roof drains is controlled by orifices or slits in the drain ring.  The roof deck must be designed to withstand the live load and be properly waterproofed. Green Roofs  A green roof, in simplest terms, is a vegetated roof.  Installation generally consists of a waterproof membrane installed over a suitably constructed roof deck.

18. Questions/Answers

19. Cottage Grove Pilot Study  Funded by TCEQ Section 319 Grant  Partnered with data collection by UH  Looks at Nonpoint Solution Issues  A true research project  Focus on simple two block area (TBD)  Alternative LID Technologies Effectiveness (Quantity/Quality) Cost of Installation Cost of Maintenance  Competitive Space Requirements in ROW Parking vs. Drainage vs. Mobility

20. Cottage Grove Area

21. How, When, and Why  UH and Rice are currently collecting pre-project data for the neighborhood  Council approved the TCEQ contract on 5/4/2010  Evaluation of capabilities of LID techniques for water quantity/quality  Post construction data to compare to pre-data for effectiveness  Construction in late 2012  Findings may provide options for future Neighborhood Street Reconstruction projects or Developer Sponsored projects.

22. Questions/Answers