Natural Water System - Drainage and Harvesting

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What is It?

Water cycle.jpg

This is fundamentally about our stewardship of the water in the natural water system, which is vital to our sustainability. Today, by code, the rain that falls on the Green Garage building and site is required to be retained on the site or placed in the storm drains. These storm drains run into our rivers and lakes, bypassing the natural cleaning system of the wetlands and percolation into aquifers. By all accounts, this is destroying our lakes and rivers. A recent study showed it will take $2 billion to clean up the Great Lakes and the EPA has cited urban runoff, with its associated pollutants, as one of the top contributors to the decline in the health of our lakes.

This is about harvesting the water we need for plants and trees and returning the remainder to the water table cleaned for future generations. This requires an integrated drainage system to carry rain water off the building, storing some of it for future use and directing the remainder of it to drainage fields where it can be cleaned and absorbed into the soil, and eventually the water table. So the elements of this are:

  • Water conservation ... reducing our demand for water
  • Green garden roof ... growing plants and food on the roof.
  • Roof drainage system ... how to get the rainwater off the roof.
  • Ground drainage system and percolation the water that falls on the ground and is redirected from the roof will be returned to the water table.
  • Rain water storage (rain barrels, cisterns)...the rain water that is stored for use to water plants or flush toilets.

Also known as: rain water harvesting, storm water management

Why is it Important?

  • Strengthens our understanding and relationship with water.
  • Helps restore the planet's natural water system and improves the quality of water for future generations.
  • Reduces the usage and associated costs of water from the public water system.
  • Creates One Earth Patterns for water that others can use.

When to Use It?

  • Virtually every built environment has a relationship with water that warrants special care.
  • The more roof or impermeable surfaces you have, the more important this pattern becomes.
  • Use water conservation methods first to reduce your demand for water
  • Storing water should only be used if there is a clear proportionate demand for the stored water.

Green Garage Use of Natural Water System - Drainage and Harvesting

Sustainability Goals

  • Return 100% of the rainfall to the ground water table.
  • Capable of handling the volume of water generated by up to a 10 year storm event.
  • Clean the rain water before it re-enters the aquifer.
  • Harvest rain water adequate to meet the watering needs of plants and trees on the Green Garage site.
  • Develop connections between people and the natural water cycle.
  • Use zero city supplied water for outside purposes.


  • Determine how much rain falls in our area and what the storm water drainage requirements are for Detroit
    • 10 Year Daily = approx 3.0" of rain per day in Detroit.
    • 25 Year Daily = approx 3.7" of rain per day in Detroit (see reference site here)
    • 100 Year Daily = approx 4.7" of rain per day in Detroit. (see reference site here)
    • 100 Year Hourly = 2.48" of rain per hour in Detroit. (per Michigan Dept of Transportation)
  • Learn how the water flows on the current site and building.
    • Create a water map showing how the water currently flows.
  • Minimize the Demand for Water
    • Grow native plants and trees that clean the rain water and minimize the water demand.
  • Harvested Water Strategy
    • Harvest water for the plants in reused barrels and storage tanks.
    • Store the harvested water close to where it will be used.
    • Begin with a moderate amount of water stored and increase as the need arises.
  • Percolation Field
    • Create percolation fields in the parking lot and front of the building where the demand for water is highest due to the sun and plants.
  • Building drainage
    • Move as much to the front as possible...this is where the sun is.
    • Leave the storm drainage as a backup capacity, especially in the truck well.
  • Overflow
    • Every retention and storage area will have an overflow into the public storm drains.
    • The overflow will be placed before the storage and retention areas.

Conceptual Design

Overall Design
Green Garage - Natural Water System: Drainage and Harvesting

The overall natural water system design is driven by the rain fall requirement. We set the rainfall requirement at 3 inches per day or 1 inch per hour. This is very close to the 15 year requirements, (which needs confirmation...this is harder to do than we thought.)

Taking this requirement and our strategy (above) we developed the overall water drainage and harvesting design shown. change storm drain to storm drain on image (spelling)

Our current calculations indicate that we will put some rain water into the public storm drain only once every 15 years. Our calculations are available in this google spreadsheet...Water Analysis.

Rainfall Requirements Estimation
  • 10 Year Storm Requirements

Detroit Monthly Precipitation (includes snowfall)

  • (Note that over a period of 57 years, 99.9% of the daily rainfall amounts have been less than 3").
Detroit Daily Precipitation - 1948 - 2005 US Climatology Historical Network

Detroit Monthly Precipitation Average Monthly
1.91" 	1.88" 	2.52" 	3.05" 	3.05" 	3.55" 	3.16" 	3.10" 	3.27" 	2.23" 	2.66" 	2.51"
TOTAL 32.89"
Detroit Monthly Precipitation Actual 2007
3.02" 	0.82" 	3.09" 	2.68" 	2.56" 	3.10" 	2.10" 	6.61" 	1.44" 	2.00" 	1.77" 	3.48"
TOTAL 32.67"
Detroit Monthly Precipitation Actual 2006
3.24" 	2.71" 	3.21" 	2.71" 	4.6" 	3.95" 	4.38" 	2.05" 	1.73" 	4.11" 	2.9" 	3.65"
TOTAL 39.24
Detroit Monthly Precipitation Actual 2005
3.40" 	3.02" 	0.74"	1.66" 	1.85" 	1.95" 	5.38" 	1.33"	1.63" 	0.13" 	4.70" 	2.52" 	
TOTAL 33.58"
Detroit Monthly Precipitation Actual 2004
1.43" 	0.63" 	3.29"	0.69" 	8.46" 	2.86" 	2.85" 	4.52" 	0.65" 	2.08" 	3.21" 	2.91" 	
TOTAL 28.31"
Detroit Average Monthly Snowfall
11.9" 	9.3" 	7.0" 	1.7" 	Trace 	0" 	0" 	0" 	0" 	0.3" 	2.7" 	11.1"

  • Climatic Sources

NOAA's National Weather Service Weather Forecast Office

Storm Water Flow Maps
Area Natural Rainwater Flow on July 12, 2008

Roof Drainage

All roof drainage is currently designed to go into the storm drains. Over the years the drains have stopped up and the owners at the time resorted to putting gutters on the building. These gutters have since seen their day and most have large holes.

Our new water plan, (see diagram), is to divide the roof into sections to have the water go to where it can be stored, used or placed into the drainage fields for the plants around to use.

Retention/ Drainage Fields

We are using a retention/drainage field in the front yard area, parking area and backyard area to retain water and allow it to infiltrate into the water table. These areas will be planted with native species that like the water and have properties to clean the water before it enters the water table. The soil will be designed with courses that provide adequate drainage capacity. Our current design is for the following courses:

  • The Parking Area and Front area courses would be:
    • Brick / Crushed stone (3.5")
    • Crushed stone bedding (2")
    • Crushed stone open-grade (4")
    • <<Any drainage pipe 12" and 4" would be laid here>>
    • Natural Stone open grade (16")
    • (Optional) geo-tech fabric
  • The Backyard courses would be:
    • Grass + Topsoil / Crushed stone (3.5")
    • Crushed stone open-grade (4")
    • <<Any 12" or 4" drainage pipe would be laid at this level>>
    • Natural Stone open grade (16")
    • (Optional) geo-tech fabric
Absorbtion Rates / Perc Tests

We are doing a percolation test on the site to determine the absorption rate of the soil. The results will be posted here when they are available. Our research indicates that the absorption rate of clay seems to vary a little depending on the source.

Clay Infiltration rates of:

Other Soil Type Infiltration Rates:

  • Sand: 1.5 - 6.0 inches/hour
  • Silt: 1/2 inch/hour

We did our most complete perc test on Friday, June 26th. Here's a video describing the process.

We performed a water absorption test in the backyard on June 22, 2009 to determine what type of soil we currently have. The following procedure is from the University of Wisconsin – Madison Arboretum site:

Perform the following infiltration test at each location selected.

  1. Dig a hole 6 inches deep by 6 inches in diameter.
  2. Fill hole with water and let stand for one hour.
  3. Refill hole with water. Measure depth of water with a ruler.
  4. Let stand 1 hour. Then measure the depth again.
  5. Use the following chart to determine soil types based on the rate at which water soaks into the soils.

The results of the test were:

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Storage / Usage

Our current water harvesting plan calls for the following storage tanks:

  • 500 gallon tank on the side of the building near the truck well at 12 feet high. It will act as the water supply for the front of the building. The pressure will be approximately 20 psi (normal city water supply is in the 40 - 60psi range)
  • 2,000 gallon tank underground in the backyard near the alley (SE corner.) This would be used as a water source for the backyard plantings, the green alley plants, water to flush toilets and a community rainwater well.
  • Ten 55 gallon rain barrels. Most would be placed on the roof where the water would be needed most to water plants (e.g. flowering and food). Some rain barrels in the backyard near the compost bin for cleaning and watering plants.

We found little publicly available information about the water requirements of native plants exposed to natural watering. We feel the main plants needing water are on the roof garden and the alley. Our most current work is this:

  • Garden Beds Water Needs
    • Assumptions:
      • Native plants in the wild don't need to be watered. Then they can survive on on average of 3" a month in Michigan May - Sept.
      • Front Bed and front of Annex: because of the extreme heat island in the front of the buildings those areas will need 4" of rain per month.
      • The roof gardens will need 3" of water applied to the roots per month.
      • If we store the equivalent of one week's need: 1" for the front and parking area and .75" for the alley and .5" backyard (obtained either from rain or gray water) the following shows the rain barrel need.
    • 1 Week's Water Needs by Garden Area:
      • Front Bed: Area: 254 sq ft, Gals needed(1")= 159, Rain Barrels (55 gal): 3
      • Parking Lot: Area: 892 sq ft, Gals needed(1")= 555, Rain Barrels (55 gal): 10
      • Alley: Area: 744 sq ft, Gals needed(.75")= 349, Rain Barrels (55 gal): 6
      • Backyard: Area: 721 sq ft, Gals needed(.5")= 225, Rain Barrels (55 gal): 4
      • Roof Gardens: Area: 300sf, gals needed (2") = 375, Rain Barrels (55 gal): 6
    • If we can supplement the rainwater with a steady supply source, i.e. gray water, the storage size need could be reduced. (a half week supply or a couple day supply)
    • Further Considerations:
      • Green Garage soil absorption rates
      • insulation around cement to decrease island heat effect?
Water Distribution

We are currently planning to move the harvested water around the site to the point of use without any power. The specific plans are:

  • Front / Parking Area / Wall Gardens - will use a hose attached to the elevated tank on the side of the front building. We estimate that there will be 20 psi of pressure available from the tank.
  • Back yard / Alley - will be from the large tank (2,000 gal) underground in the south end of the back yard. It will be pumped up with a hand pump into buckets or hoses into the gardens.
  • Garden Workshop / Garden Roof - the water will come from faucets connected to the rain barrels. It will go into buckets / watering cans that will be carried to where it's needed.

As indicated in our strategy, there will be overflow connections to the public storm drain system at each downspout. They will connect into our existing storm drains, in either the building or in the truck well. This means that if the storage and drainage fields can not handle the amount of rain, the overflow will go into the storm drains.

Supporting science:

Proposed Materials / Suppliers

  • Look at suppliers of flexible drainage pipes in Earth Tubes Proposed Materials / Suppliers.
  • Narrow water tank supplier in Austin Tx. Blue Scope Water.

Development Story

The Natural Water System - Drainage and Harvesting - Development Story page contains many images and videos documenting the process used at the Green Garage to design, build and operate our ?? system.

Related Internal Links

  • Help people find other related Green Garage pages that may help them. Keep it tight.


To Do's


  • Evaporated Sprayer System for passive cooling of the roof
    • Autocool Roof System ... indicates a 50 - 70F reduction in roof temp saving 20 - 30% cooling load.
    • Cool Roof Article excellent stats...including "On average, the roof accounts for 35% to 40% of a building's total heat load." This article reinforces the findings above.
    • It could be PV operated because it would be hottest on a sunny day.
    • Solar Shield product
  • Micro-irrigation
  • Hydroponics Gardening
  • In strategy, clarify rainfall amounts - I didn't understand the numbers. Thought you meant we get 3 inches of rain every day. (Peggy)
  • On water flow chart, change stromdrain to storm drain (Peggy)
  • Add data for second soil absorption test (Peggy)
  • In garden bed water needs, I questions your numbers about parking lot needs. Number seems high. Remember, most of parking lot area will be brick and gravel. (Peggy)

Peggy edited this page :)