Passive Water Harvesting at the Blue Moon Garden
What is “Passive”
Rainwater Harvesting?
Why Harvest Rainwater?
Passive rainwater harvesting is the practice of redirecting
the natural flow of rainwater off impervious surfaces such
as rooftops and paving into swales and basins where it
can infiltrate into the ground for use by landscape plants.
It does not require any “active” elements such as storage
tanks or pumps.
As the population increases so does the demand for
fresh drinking water. Utilizing rainwater or other nontreated water sources for landscape irrigation can help
reduce this demand. Collecting and using rainwater on
site has many benefits: it reduces potential for flooding
and erosion, and replenishes local groundwater
reserves. Rainwater is also free of salts that are dissolved
in groundwater. Using rainwater for irrigation flushes
accumulated salts down and out of the plant’s root
zone which encourages better root development and
drought tolerance.
The Blue Moon Garden has been designed to take
advantage of the existing topography, which slopes
southeast to northwest. Micro-basins have been designed
to capture rainwater that flows across the site. In addition,
the roof of the shed and half of the ramada roof have
been designed to drain into micro-basins.
Mulch
The dry air in Tucson has the capacity to evaporate
seven times the annual rainfall we receive. Mulches
improve the efficiency of water harvesting by reducing
evaporation from soils.
Mulches can be organic or inorganic. Organic mulches
include wood chips, bark, or other vegetative material.
Plant litter such as seeds, leaves, flowers, and branches
that fall off of plants will replenish the inorganic mulch
over time if it is allowed to accumulate. Inorganic mulch is
decorative rock or rip rap that has had the fine grained
material, which can inhibit infiltration, screened out.
At the Blue Moon Garden, inorganic mulches are used
in the micro-basins.
Curb Cuts or Curb-less Paving
The parking lot at the Blue Moon Garden does not have
a continuous curb. This allows the water that flows across
the site to move into the planting areas.
Xeriscaping
Xeriscape is the practice of using native and drought
tolerant plant species in the landscape. Rainwater
harvesting and xeriscape go hand in hand in reducing
the use of potable irrigation water in the landscape.
Native plants require less water, are better adapted to
our seasonal rains, and provide shelter and food for
native animals. Care should be taken in selecting and
locating plants for use in conjunction with micro-basins.
Some species are more tolerant of having “wet feet”
than others. At the Blue Moon Garden, the native plants
were selected to attract native species such as bees,
butterflies, moths, and hummingbirds that will help to
pollinate the vegetable and fruits gardens.
Micro-Basin
Passive rainwater harvesting is relatively inexpensive and
easy to maintain and is a good choice for sites that have
adequate space for basins and swales.
Micro-Basins
Xeriscape Area
Micro-basins are depressed areas in the landscape that
temporarily store rainwater collected from impervious
surfaces. Commonly, micro-basins are positioned so
water flows directly into them from roofs, sidewalks, or
patios. Water can also be directed into micro-basins
through swales or french drains that carry the water to the
basin from somewhere else on the site. Micro-basins are
typically lined with mulch and designed to allow water to
percolate into the soil within a day.
Micro-basins at the Blue Moon Garden are located
in the parking lot, along the front walk, and next to the
ramada. Larger basins collect storm water flowing across
the site to supplement the irrigation of the fruit trees and
the native plant garden on the east side of the site.
Active Water Harvesting at the Blue Moon Garden
What is “Active”
Rainwater Harvesting?
Why Harvest Rainwater?
As the population increases so does the demand for fresh
drinking water. Utilizing rainwater or other non-treated
water sources for landscape irrigation can help reduce
this demand. Collecting and using rainwater on site has
many benfits: it reduces potential for flooding and erosion,
and replenishes local groundwater reserves. Rainwater
is also free of salts that are dissolved in groundwater.
Using rainwater for irrigation flushes accumulated salts
down and out of the plant’s root zone which encourages
better root development and drought tolerance.
Monitoring
Tucson House
Cistern
Blue Moon
Garden Cistern
Tucson House Cistern
Collection Area
for Rainwater
As our water resources become scarce, it will be
increasingly important to innovate ways to conserve
water. Several monitoring devices have been
incorporated in the design of the system at the Blue
Moon Garden to provide information about the true
costs of harvested rain and condensate water.
The Tucson House is the seventeen story building
located to the north of the garden. The active rainwater
harvesting system at the Tucson House is collecting
rainwater from an approximately 6,000 square foot
area on the roof into an existing 15,000 steel tank from
when the Tucson House was utilizing well water. Based on
Tucson’s average rainfall of 12”, this system can collect
an average of 45,000 gallons of water per year.
Irrigated by
Rainwater
A separate electrical meter has been included to
monitor the electricity usage and cost. This meter will track
the electrical use of the following: rainwater harvesting
pumps, irrigation brain boxes, and the irrigation controller.
A pump will send the water to the cistern at the garden
via an underground pipe. A set of devices called “brain
boxes” monitor the water level in each of the cisterns
and turn the pump on and off as needed to replenish
the water in the cistern at the garden.
Flow meter sensors track the water usage from the cisterns
and the potable water supply. The flow sensors track
water usage like a potable water meter, but also work in
conjunction with the irrigation controller to shut down the
irrigation system when there is an abnormal flow,
i.e., a break in the irrigation line.
6,000sf Roof
Ramada
300sf Roof
“Brain Box”
“Smart” Irrigation
Condensate
“Brain Box”
The irrigation controller at the Blue Moon Garden is a
“smart” controller, which offers efficient watering modes,
flow management, and weather sensing. The irrigation
controller will “learn” the normal flow and provide alerts
of low or high flow scenarios and shut down in a rain
event.
Soil moisture sensors have been located in the community
garden beds, citrus grove, and a passive rainwater
harvesting basin. The soil moisture sensors will prevent the
irrigation controller from activating if there is adequate
water present at the root zone of the plants, such as
after a rain event.
Active rainwater harvesting involves collecting rainwater
off of rooftops into a container such as a cistern or
barrel so that it can be used as needed to irrigate
the landscape. Cisterns are designed to prevent light
or mosquitoes from entering and causing health issues.
Active rainwater harvesting is a good choice for sites
where there is not enough space for basins or when it is
preferable to store the water for future use.
Float
Float
2,000 Gallons
15,000 Gallons
Pump
Pump
A by-product of air conditioning is water that condenses
within the unit. Historically at the Tucson House (and most
buildings), this water drained into the sewer system where
it is essentially thrown away. Condensate water differs
from rainwater in that it creates a constant low flow of
water. This is significant for two reasons: one, over time
this little flow can accumulate into a significant amount
of water, and two, this water is produced during the
warm months when the air conditioning units are running
and the irrigation water demand is at its highest.
Blue Moon Garden Cistern
To Landscape
for Irrigation
Garden Cistern
Tucson House Condensate
Water Harvesting
Tucson House Cistern
Half of the roof area of the garden ramada will flow
into the cistern by the ramada. This system can collect
approximately 2,000 gallons of water per year based on
an average of 12” of rain. This system will tie directly into
the drip irrigation system and will provide supplemental
water to the native landscape areas and citrus grove.