CITY OF HOUSTON

FLOODING & DRAINAGE COMMITTEE

PUBLIC WORKS AND ENGINEERING

May 18, 2010

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

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

Bioretention Basin

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.

Porous/Pervious Concrete

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.

Porous/Permeable Pavement Installations

Rice University Campus – sidewalks Rice University Parking Lot –

Combination of porous pavement and BioSwales

Cliff Tuttle Park – Permeable Pavers

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.

Dry Swale

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.

Dry/Bio Swales Installations

Rice University Parking Lot Kendall Library Parking Lot Federal Reserve Bank Building MFAH – Bayou Bend Hermann Park Plaza

Wet Swale

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.

Rain Barrel

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

Hard Roofs/Green RoofsHard 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.

Questions/Answers

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

Cottage Grove Area

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.

Questions/Answers