Bioretention / Rain Garden Design & Development in Hawaii

Presented By:Lauren C. Roth Venu

808-781-7583lauren@rothecological.com

www.rothecologicaldesign.com

Picture by: The Daily Kos

SITE ASSESSMENT•What type of Project (New, Redevelopment, or Retrofit)?•Greenfield or Brownfield?•What are the current drainage patterns?•What are the potential pollutants of concern?•Are there “sensitive” ecosystems on or downstream of the property?•How will the development or redevelopment impact the predevelopment conditions (new development)•Slopes steep? How vegetated? With what type of vegetation? •Water Balance-How much water could be collected and is there a cost-benefit for storage to (re)use.•For Retrofits- What landscapes are in place that could be converted to an ecological LID best management practice?•What are the rainfall patterns?•What are the types of soils?•Other?

When ‘recharge’ is not possible

Soil infiltration rate less than 0.5 inches/hourSoil infiltration rate greater than 3

inches/hourKnown man-made plumes or contaminated

soilsPotential for concentrated

pollutant/chemical spillsLess than

3 ft. to high ground water table 50 ft. to groundwater drinking well 35 ft. to septic system20 ft. to building foundation10 ft. to property line100 ft to down-gradient building foundationSlide by: City and County of Honolulu

Land Use Impacts: ex. Agriculture

Plant & Substrate SelectionSoil & Plant Mixes:•What are the pollutants of concern?•What is the natural drainage of the site? •Storage capacity•Biochar & mycelium•Native Plants•Plants with good root structure•Phyto/bioremediation

Rainfall Variance

USGS

DBEDT

NOAA (PFDS)

Is the 1’’ 24hr storm event = to the 90th-95th percentile event?Managing Quality: 85th and 95th Percentile, 24-hour; and 100-yr, 2-hour storms (Source: City and County of Honolulu

• Kaneohe 0.78” 1.81” 5.56”• Kailua 0.80” 2.01” 5.95”• Hawaii Kai 0.92” 2.00” 4.61”• Manoa 0.70” 1.42” 5.91”• Punchbowl 0.70” 1.48” 5.29”• Ewa 1.19” 2.33” 4.67”• Waianae 1.25” 2.50” 4.29”• Wahiawa 0.80” 1.64” 5.68”

Water Quality Volume

• P= Rainfall event (90-95 percentile)• Rv = Runoff Coefficient • A = the Contributing

Area

• Qa = Runoff Volume (inches)A

WQQ Va

Stormwater: Quantity

20yr storm is now every 3-5yrs!

Education & Outreach

Navigating through permitting!

Source: “Stormwater Management the Natural Way: Guide to Low Impact Design and Development”

Case Study 1: Kalepolepo Beach Park/Maui NOAA Whale Sanctuary, Kihei, Maui

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Case Study 2 (Retrofit):Windward Mall, Kaneohe, Oahu

Pre-existing Conditions

Drainage Area & Design Storm Volume

(3) Bioretention Systems

Grading

Connecting to existing storm sewer

Engineered Soil & Stone Spillways

Planting

Construction (close to) pau