1. Bioretention / Rain Garden Design & Development in Hawaii
Presented By:
Lauren C. Roth Venu

2. Picture by: The Daily Kos

3. 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?

6. When ‘recharge’ is not possible
Soil infiltration rate less than 0.5 inches/hour
Soil infiltration rate greater than 3 inches/hour
Known man-made plumes or contaminated soils
Potential for concentrated pollutant/chemical spills
Less than
3 ft. to high ground water table
50 ft. to groundwater drinking well
35 ft. to septic system
20 ft. to building foundation
10 ft. to property line
100 ft to down-gradient building foundation
Slide by: City and County of Honolulu

7. Land Use Impacts: ex. Agriculture

8. Plant & Substrate Selection
Soil & 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

9. Rainfall Variance
DBEDT
USGS
NOAA (PFDS)

10. Is the 1’’ 24hr storm event = to the 90th-95th percentile event
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” ” 5.56”
Kailua ” 2.01” 5.95”
Hawaii Kai 0.92” 2.00” 4.61”
Manoa ” 1.42” 5.91”
Punchbowl 0.70” 1.48” 5.29”
Ewa ” 2.33” 4.67”
Waianae 1.25” 2.50” 4.29”
Wahiawa 0.80” 1.64” 5.68”

12. Water Quality Volume P= Rainfall event (90-95 percentile)
Rv = Runoff Coefficient
A = the Contributing Area
Qa = Runoff Volume (inches)

14. Stormwater: Quantity
20yr storm is now every 3-5yrs!

15. Education & Outreach

16. Navigating through permitting!
Source: “Stormwater Management the Natural Way: Guide to Low Impact Design and Development”

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

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

19. Pre-existing Conditions

20. Drainage Area & Design Storm Volume

21. (3) Bioretention Systems

22. Grading

23. Connecting to existing storm sewer

24. Engineered Soil & Stone Spillways

25. Planting

26. Construction (close to) pau