CITY OF HOUSTON

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 – IDMStormwater 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. Bioretention Basin 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. Porous/Pervious Concrete • 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