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Santa Monica CA Rainwater Harvesting Manual
City of Culver City Rainwater Harvesting Program
Table of Contents
Introduction .....................................................................................1        Before you Begin ...................................................................................9
Background ........................................................................................... 1   Assess Potential Sites ............................................................................9
What is Rainwater Harvesting? .............................................................1               Design .................................................................................................... 9
Who Should Use this Manual? ..............................................................1                Perform a Soils Infiltration Test .............................................................10
Why Harvest Rainwater? ..................................................................2                 Calculate Runoff and Rain Garden Size..................................................10
To Protect Our Bays and Ocean .............................................................2               Direct Water Flow..................................................................................10
To Reduce Energy Demands ..................................................................2               Choose your Plants ................................................................................10
To Practice Water Conservation ............................................................2               Plants for Southern California ...............................................................11
To Recharge Groundwater Supplies.......................................................2                   Build your Garden .................................................................................12

Overview of Rainwater Harvesting ...................................................2                      Other Rainwater Harvesting Options ................................................13
Redirection Options...............................................................................2        Rainwater Harvesting System Maintenance ......................................14
What is a Rain Barrel? ...........................................................................2        Rain Gutters ........................................................................................... 14
What is a Rain Garden? .........................................................................3          Downspouts .......................................................................................... 14
How to Harvest Rainwater on Your Own ...........................................4                          Rain Barrels ........................................................................................... 14
Assess your Site .....................................................................................4    Rain Gardens ......................................................................................... 14
Redirection Criteria Checklist and Safety Considerations ......................4                           Where Can I Get More Information? .................................................15
How to Measure a Slope .......................................................................4            The City of Culver City ...........................................................................15
How to Redirect a Downspout to a Pervious Area .............................5                              Additional Resources .............................................................................15
Before you Begin ...................................................................................5      Glossary of Terms ..................................................................................15
Redirection Procedure ...........................................................................6
How to Redirect a Downspout to a Rain Barrel .................................7
Before you Begin ...................................................................................7
Redirection Procedure ...........................................................................8
How to Build a Rain Garden ..............................................................9



            Rainwater Harvesting Program                                                                                                                                                                                   i
Introduction                                                    impervious surface such as a sidewalk, driveway
                                                                or parking lot.
Background
                                                                Rainwater harvesting is the process of inter-
The City of Culver City Rainwater Harvesting
                                                                cepting rainwater from a roof (or other surface)
Program is designed to help homeowners learn
                                                                and putting it to beneficial use. By implement-
to capture rainwater for beneficial use, and
                                                                ing the harvesting techniques in this guide,
reduce the amount of rainwater flowing from
                                                                homeowners gain an extra water supply while
their roofs into the storm drain system. The
                                                                simultaneously reducing the pressure on our
Program calls for disconnecting downspouts
                                                                limited water supplies.
that discharge to impervious areas and redirect-
ing them to areas where rainwater can perco-                    Who Should Use this Manual?
late into the soil, or collect into rain barrels.               This guidance manual will help homeowners
Due to heavy groundwater usage in Southern                      implement the first steps of harvesting rainwa-
California, approximately 3.2 million-acre feet                 ter. It contains “How-to” information for the
of space are available for groundwater re-                      homeowner interested in disconnecting down-
charge. That is equal to 12,000 Rose Bowls filled               spouts to capture and use rainwater. By follow-
to the top with water. A recent study described                 ing the step-by-step instructions homeowners
soil conditions in most of the Southern Cali-                   can: (1) disconnect existing downspouts; (2)
fornia region as highly permeable, allowing for                 extend downspouts to areas that can infiltrate
rapid infiltration into groundwater basins1. The                rainwater; (3) install a rain barrel; and (4)
rainwater harvesting process described in this                  construct a rain garden or other infiltration
“How-To” Guide will help increase local water                   mechanism. Homeowners looking to imple-
resources by promoting groundwater recharge.                    ment additional rainwater harvesting methods,
                                                                or seeking supplemantal “How-to” or trouble-
What is Rainwater Harvesting?                                   shooting information should refer to Additional
Many residential and commercial properties                      Resources provided in this guide. The program
in the City of Culver City are fitted with down-                website (CCrainwater.ballonawatershed.org)
spouts. When it rains, water runs off roofs,                    will be updated with useful information as well.
through these downspouts and usually onto an
1
  Natural Resource Defense Council Technical Report. A Clear
Blue Future: How Greening California Cities Can Address Water
Resources and Climate Challenges in the 21st Century. August                                                       © 2009 G3LA
2009.
          Rainwater Harvesting Program                                                                                           1
Why Harvest Rainwater?                                         Using rainwater to water plants helps conserve
                                                               dwindling drinking water supplies.
To Protect Our Bays and Ocean
When rainwater flows from a downspout onto                     To Recharge Groundwater Supplies
our sidewalks, driveways and streets, it collects              Approximately 40% of Southern California’s
a variety of pollutants. By capturing rainwater                drinking water comes from groundwater.
that falls on roofs, landowners help reduce the                Harvesting rainwater and allowing it to infiltrate
amount of runoff ultimately reaching the Santa                 into the ground replenishes our groundwater
Monica Bay, and thus aid in improving the qual-                supplies.
ity of our local surface waters.                               Overview of Rainwater Harvesting
To Reduce Energy Demands                                       Redirection Options
The State of California Energy Commission                      The City suggests redirecting stormwater runoff
reported that water-related energy consump-                    from downspouts to either a rain barrel or an
tion in California accounts for nearly 20% of the              on-site pervious area such as a flower bed or
State’s electricity, 30% of its natural gas, and               rain garden as “first-steps” in the rainwater
requires about 88 billion gallons of diesel fuel               harvesting process. There are many more
every year 2. One inch of rain falling on 1,000                features that can be implemented on a residen-
square feet of rooftop produces more than 600                  tial property to capture and utilize rainwater.
gallons of water. If homeowners replaced this                  Please refer to the Sections: Other Rainwater
amount of potable water with captured rain                     Harvesting Options and Additional Resources
water, energy consumption in the State should                  for more rainwater harvesting ideas.
be reduced.
                                                               What is a Rain Barrel?
To Practice Water Conservation                                 Rain barrels store rainwater from roofs for
California has entered an era of increasing                    reuse in landscape irrigation. Rain barrels
water scarcity, coupled with projections of                    are containers typically made of a heavy duty
increased temperatures up to 10 degrees                        plastic and can range in size from the standard
Fahrenheit by the end of this century.2                        55 gallons to more than 80 gallons. Eco-friendly
2
  The State of California Energy Commission. California’s      rain barrels assembled from recycled food bar-
Water-Energy Relationship Final Staff Report. November 2005.   rels or manufactured from recycled plastics are
(http://www.energy.ca.gov/2005publications/CEC-700-2005-
011/CEC-700-2005-011-SF.PDF)                                   available to consumers.

          Rainwater Harvesting Program                                                                              2
Key components of a rain barrel include the         • Rain barrels must be accessible for periodic
following:                                            cleaning.
• A screen to keep debris and mosquitoes out        Information on where to purchase a rain bar-
• A spigot                                          rel and rain barrel pricing can be found on the
• An overflow                                       City’s website at:
• A connector for linking multiple rain barrels     CCrainwater.ballonawatershed.org
  (if desired).
                                                    What is a Rain Garden?
Rain barrels are typically placed below down-
spouts and must meet the following require-         Homeowners can maximize both environmen-
ments:                                              tal and economic benefits by installing a rain
                                                    garden in place of a grassy or impervious area.
• Rain barrels should not allow UV light pen-
                                                    A rain garden is a shallow depression that cap-
  etration in order to prevent algae growth;
                                                    tures rainwater and allows it to soak into the
• Rain barrels must be covered and any open-
                                                    ground. Plants help to filter harmful pollutants
  ings must be screened to prevent mosquito
                                                    in the the rainwater as it moves through the soil
  breeding; and
                                                    layer. A rain garden is most often planted with
                        Downspout                   native species creating a natural ecosystem on
                                                    properties where birds, butterflies, and benefi-        Swale
                                         Overflow
                               Screen    Valve      cial insects thrive. Rain gardens also capture
                                                    sediments carried by rainwater, preventing
                                                    them from clogging the stormdrains.
    Barrel



    Spigot

                          Multi-barrel
                          Connector
                                                                                                        A swale directs water from the downspout to
                                                                                                        the rain garden. Many swales use rocks that
A typical rain barrel set up                                                                            create a dry creek bed look.
         Rainwater Harvesting Program                                                                                                                 3
How to Harvest Rainwater                            As a guideline, locate downspouts:
on Your Own                                         • At least 3 feet away from public sidewalks;
                                                    • At least 5 feet away from property lines;
Assess Your Site                                    • At least 5 feet away from house foundations                   300 ft2
Preparing a site sketch will help to determine        and crawl spaces, assuring at least a 2% slope
downspouts to disconnect. Begin by drawing            away from the home;
an outline of the home from a bird’s eye view.      • At least 6 feet away from basement walls.
Walk the perimeter and mark the location of                                                                 Downspouts
all downspouts on your sketch. Note which           How to measure a slope:
downspouts are connected to rain gutters;           Tie a level string to two stakes pounded into the
these downspouts are candidates for discon-         ground. Make certain that the string attached
nection. Draw in roof lines, and estimate the       to the uphill stake is at ground level. Measure     Figure 1: Example sketch of site
square footage of the roof area (Figure 1).         the distance between the stakes. This is consid-
                                                    ered the width. Measure the distance from the        Example of Roof Area Calculation:
Redirection Criteria Checklist and Safety           string on the downhill stake to the ground. This                          Lr = 25 ft   Lt = 10 ft
Considerations                                      is the height. Make certain that the height and
It is suggested that the following list of condi-   width are the same units. Divide the height by         Wr, Wt = 10 ft
tions are met in order to safely redirect a down-   the width to get the slope. Multiply this by 100
spout from a roof to a pervious area without        to obtain the percent slope. (Figure 2)                Roof Area = (Lr x Wr) + 1/2(Lt x Wt) =
damaging building foundations, or flooding a                                                                 250 (square feet) + 50 (square feet) =
basement or neighboring properties.                                                                          300 (square feet)
As a guideline, direct downspouts:
                                                                                                                          Height ÷ Width = Y
• To gently sloped areas (preferably 10% slopes      Example of Slope Calculation:                       Downhill          Y x 100= % slope             Uphill
  or less – See How to measure a slope);                                                                  Stake                                         Stake
• To areas sloping away from buildings;                Height = 6 inches = 0.5 feet                                           Width 10’
• To rain gardens (See How to Build a Rain             Width = 10 feet                                                          String
  Garden);
                                                       0.5 feet ÷10 feet= 0.05
• Never above septic tanks;                                                                                    Height 6”
• Never to areas that experience ponding;              0.05 ×100 = 5% Slope
• Never to fill areas.
                                                                                                        Figure 2: How to measure a slope
        Rainwater Harvesting Program                                                                                                                             4
How to Redirect a Downspout to a Pervious Area
Before you Begin
Prepare all of the tools and materials that you need. It is best to use                              Hacksaw          Tin snips
durable, gutter-grade materials, such as ABS Schedule 40 plastic options.                                                                     Drill
                                                                              Bracket
Other materials such as corrugated black plastic, PVC pipe, or dryer hose
can be used but tend to be less durable. Consult a home and garden
specialist when purchasing materials for further assistance. See the list
below and Figure 3 for tools and materials you will need. Be sure to                                                                   Screw driver
                                                                                                 Needle-nose        Tape measure
wear safety glasses.                                                           Elbow                pliers

                                                                               Downspout
                                                                               extension
              Tools:                   Materials:
                                                                                                                     Sheet metal       Safety glasses
              • Hacksaw                • Downspout                                      Splash                         screws
              • Tin snips                extension                                      guard
              • Drill                  • Sheet metal screws
              • Needle-nose pliers     • Elbow                               Figure 3: Materials and tools for redirecting the downspout
                or crimpers            • Bracket
              • Tape measure           • Splash guard                                       Gutter
              • Screwdriver or nut
                driver
              • Safety glasses


                                                                                                               Downspout
Select downspouts to disconnect that are connected to a rain gutter
(Figure 4). Some homes in the City of Culver City are not fitted with rain
gutters. If a home does not have rain gutters along the perimeter of the
                                                                                Extension
roof, homeowners might consider installing them. This guidance manual
does not provide information on how to install rain gutters because
these tasks involve roof seals and require professional expertise.
                                                                             Figure 4: Rain gutter and downspout
        Rainwater Harvesting Program                                                                                                                    5
Redirection Procedure
                                              Redirecting a downspout to a pervious area is a
                                              simple procedure.
                                              Step 1: Mark approximately 12 inches from the
                                              ground to the downspout. This height should
                                              work for up to a 6 foot extension. Cut the
                                              downspout higher for longer extensions.
                                        12”   Step 2: Using a hacksaw, cut the downspout                No basement
                                              at the mark. Remove the cut piece. You may                extension 2’
                                              need tin snips to smooth the material.
                                              Step 3: Attach the elbow over downspout. If                        Basement
                                                                                                                 extension 6’
                                              the elbow does not fit over the downspout,
                                              use crimpers or needle-nose pliers to crimp the
Steps 1-2                                     ends of the cut downspout and slide it inside        Step 4
                                              the elbow. Attach the elbow to the downspout
                                              with screws; it might help to pre-drill holes. For
                                              additional stability, consider securing the elbow
                                              to the building with a bracket.
                                              Step 4: Measure and cut the downspout exten-
                                              sion to the desired length. Attach the extension
                                              to the elbow by slipping the extension over the
                                              end of the elbow.
                                              Step 5: Use screws to attach the extension
                                              to the elbow; it might help to pre-drill holes.
                                              For additional stability consider resting the
                                              extension on a support like a cinder block. To
                                              prevent erosion, place a splash guard at the end
                                              of the downspout or direct the extension to a
Step 3                                        swale.                                               Step 5

         Rainwater Harvesting Program                                                                                           6
How to Redirect a Downspout to a Rain Barrel
                               Before you Begin
                               Make a list of the tools and materials needed. The installation of a rain
                               barrel requires materials for the downspout disconnection, and materi-
                               als to build a platform that the barrel can sit on, such as wood or cinder
                               blocks. Homeowners may also need an additional strap to secure the
                               barrel. Be sure to wear safety glasses.


                                        Tools:                     Materials:
                                        •   Hacksaw                • Downspout
                                        •   Tin snips                extension
                                        •   Drill                  • Sheet metal screws
                                        •   Needle-nose pliers     • Elbow
                                            or crimpers            • Bracket
                                        •   Tape measure           • Splash guard
                                        •   Screwdriver or nut     • Wood/cinder blocks
                                            driver                 • Securing strap
                                        •   Level
                                        •   Safety glasses



                               You can transfer water from the rain barrel to a garden by filling a water-
                               ing can, connecting a garden hose, or installing a manual drip irrigation
                               system. Water pressure at the rain barrel spigot will depend on the level
                               of the water in the rain barrel. The higher the water level, the greater
                               the amount of pressure. You can also improve flow through a hose at-
                               tached at the rain barrel spigot by elevating the barrel.



Rainwater Harvesting Program                                                                                7
Redirection Procedure
                                                         Redirecting a downspout to a rain barrel is a
                                                         relatively simple procedure.
                                       Elbow
                                                         Step 1: Decide where to locate a rain barrel.
                                                         The best place is either directly under or a few
                                                         feet from the disconnected downspout. By
                                                         attaching a hose to the spigot, a homeowner                    Measure
  Securing                                               can transport water from the barrel to another
  strap
                                                         area of the yard.
                                                         Step 2: Estimate how high the barrel will rest
                                                         under the downspout. Be sure to include the
                                                         height of the cinder blocks or platform for the
  Wood / cinder
  blocks                                                 barrel. Mark where the downspout will be cut.
                                                         Make sure to make your cut just high enough        Steps 1-3
                                                         above the rain barrel to accommodate attach-
                                                         ing an elbow.
      Hacksaw              Tin snips             Drill   Step 3: Cut the downspout with a hacksaw
                                                         so that the elbow will be inserted just above
                                                         the rain barrel inlet. You may need tin snips to
                                                         smooth the material.
   Needle-nose pliers                  Tape measure
                                                         Step 4: Assemble the rain barrel platform.
                                                         Make sure it is level.
   Sheet metal screws                   Screwdriver
                                                         Step 5: Attach the elbow over the downspout
                                                         with a screw. Secure the downspout to the
                                                         house with the bracket.
         Level                         Safety glasses    Step 6: Place the barrel beneath the elbow,
                                                         making certain that the barrel overflow valve is
Figure 5: Materials and tools needed for                 positioned in an appropriate location and away
installing a rain barrel                                 from the home. Secure the barrel to the house      Steps 4-6
                                                         with a strap.
        Rainwater Harvesting Program                                                                                              8
How to Build a Rain Garden                             Assess Potential Rain Garden Sites
                                                       Locate rain gardens where they can intercept
Before you Begin                                       and collect roof runoff. Potential rain garden
Design and build a rain garden before discon-          sites are down slope of a downspout, or adja-
necting a downspout. Helpful video instruc-            cent to an impervious surface. The following
tions for installing a rain garden are available by    factors must be considered when siting a rain
Metro Blooms at www.metroblooms.org. The               garden:
construction of a rain garden will potentially
                                                       • Build a rain garden in a relatively flat area.
result in the redistribution of soil on a property.
                                                       • Build a rain garden in a naturally low lying
As a consequence, underground utilities are a
                                                         area with good drainage.
concern. Before digging, call 1-800-227-2600 to
                                                       • Remove grass or paved surfaces to create
acquire the location of potential underground
                                                         space for a rain garden.
utilities. If a project does require the redistribu-
                                                       • Do not site rain gardens underneath the
tion of soil it may be possible to contour the
                                                         canopy of existing trees.
dirt into berms or terraces designed to slow                                                                        © 2009 Central Ohio Rain Garden Initiative
                                                       • Do not site rain gardens above septic
the flow of water. Additionally, the formation
                                                         systems.
of shallow depressions on the upflow side of                                                                A rain garden in bloom
                                                       • Do not site a rain garden where potential
the berms may trap water altogether allowing
                                                         overflow will run onto neighboring
the opportunity for it to infiltrate into the soil.                                                         1. Perform a simple soils infiltration test to
                                                         properties.
Constructing a rain garden may be an issue if                                                                  calculate the drainage rate of the potential
you live on a designated landslide or hillside         As a guideline, site the edge of a rain garden:         rain garden site.
area. Visit the Navigate LA website for a hillside     • At least 3 feet away from public sidewalks;        2. Calculate the rainfall that will run off the
area map or the Zone Information and Map Ac-           • At least 5 feet away from property lines;             portion of the roof that will be directed to
cess System (Z1 MAS) websites for area maps.           • At least 5 feet away from house foundations,          the rain garden.
Permits are not required for typical residential         assuring at least a 2% slope away from the         3. Use the example calculations to estimate the
landscaping projects. If you plan on making              home.                                                 size of your rain garden.
major landscaping modifications such as mov-
                                                       Design                                               The rain garden sizing methodology is helpful
ing more than 50 cubic yards of soil or altering                                                            for maximizing the volume of runoff captured
                                                       Size your garden: It is easy to size a rain garden
1 acre or more, contact the Culver City Building                                                            from a typical storm event. However, rain gar-
                                                       to capture a common 3/4” storm event.
and Safety Department at (310) 253-5780 for                                                                 dens smaller than the calculated size, or with
                                                       There are three key elements which are dis-
further assistance.                                                                                         slow infiltration, can also make a difference.
                                                       cussed in depth on the next page:

        Rainwater Harvesting Program                                                                                                                             9
Remember, you should always incorporate              Calculate Runoff and Rain Garden Size               Direct water flow
an overflow in your rain garden such that any        Step 4: Estimate the total roof area (RA) that      A splash guard, followed by a grassed channel
excess water, from larger storm events, will         will drain to your potential rain garden. Note      or swale, directs water from the end of a down-
flow into another infiltration area, or to the       that rooftop runoff from multiple downspouts        spout extension to the rain garden site (Page
storm drain system and away from the home’s          can be used to support one rain garden.             3). Make sure that the swale is lined with an
foundation or neighboring property.                  [RA = ___ (square feet)]                            impermeable material, such as a geotextile, if it
                                                                                                         located in the vicinity of buildings. To prevent
Perform a Soils Infiltration Test                    Step 5: Multiply the roof area by a factor of
                                                     0.65 to determine the volume of rooftop runoff      erosion and create a dry creek bed look, add
The following is a list of tools and materials you
                                                     that will flow to your rain garden.                 different sized river rocks to the swale. When
will need to conduct a soils test:
                                                     [V = RA x 0.65 = ___ (gallons)]                     the rain garden is filled with water and begins
• Measuring tape                                                                                         to overflow, direct excess water flows away
• Garden spade                                       Step 6: Plug the numbers into the equation          from buildings and neighboring properties.
• Empty gallon container                             below to determine the required size of the rain
• A watch                                            garden. If the calculated rain garden size is too   Choose your plants
Step 1: Dig a square hole two feet deep and          big for the property, improve drainage by the       There are a variety of plants that can be used
one foot wide in the deepest section of the          tilling method and recalculate the rain garden      in a rain garden. Diversity in plant selection
potential rain garden. This size works best for      size. Smaller gardens can be installed with an      will add an aesthetic quality to your garden.
the equation provided in this “How-To” Guide.        overflow. [(hours) x (gallons) x 0.008 = _____      Consider native and drought tolerant species
                                                     square footage area of rain garden]                 that adjust well to seasonal rainfall patterns,
Step 2: Fill the hole with water and let it drain                                                        and require minimal supplemental irrigation. If
completely. Fill the hole again with 5 gallons of                                                        a rain barrel is installed, the captured water can
water and monitor how fast the water drains.                                                             be used for watering plants.
Record how many hours it takes to drain the
hole. [T = ____ (hours)]                                                                                 There are several resources available for the
                                                      Example:                                           selection of rain garden plants native to South-
Step 3: Consider digging more holes in the po-                                                           ern California. Native plant nursery profession-
tential rain garden site to determine if drainage     Optimal Area of Rain Garden:                       als or garden clubs can provide assistance. The
is uniform. If drainage is too slow to measure,       T x V x 0.008 = 26 (square feet)                   Rancho Santa Ana Botanic Gardens provides
improve the drainage by tilling in a mixture of                                                          native plant palette lists and offers native plant
                                                      Where,
two-thirds sandy loam topsoil and one-third                                                              gardening workshops. Please visit their web-
                                                      T = 10 (hours)
compost to a depth of 18 inches.                                                                         site at www.rsabg.org . Other groups include
                                                      RA = 500 (square feet)
                                                      V = RA x 0.65 = 325 (gallons)                      the Water Conservation Garden at Cuyamaca
                                                                                                         College, the California Native Plant Society, The
        Rainwater Harvesting Program                                                                                                                     10
Garden Spot (bewaterwise), the Surfrider Foundation Ocean Friendly                                             where with brilliant orange flowers. Attracts
Gardens, and the Green Garden Group (G3). See the Additional Resourc-                                          butterflies and birds.
es section for more information.                                                                               Deer Grass – Grass. Likes full sun and dry to
Avoid using invasive plant species in your rain garden. Lists of invasive                                      semi-dry soil. Mixes well with wildflowers.
species can be found at the California Invasive Plant Council, Southern                                        Source of nesting materials for birds.
California region website: www.cal-ipc.org . Some trees are protected                     © 2009 Ken Gillard
                                                                                                               Coyote Bush – Shrub. Likes full sun and dry
by the City and require a special permit for removal. These include: all             California Poppy
                                                                                                               soils. Hardy and fast growing. Attracts birds
native Oak species, Black Walnut, California Bay, and California Syca-                                         and butterflies.
more. Contact the Culver City Department of Public Works , at (310)
253-5600 for more information.                                                                                 Elegant Clarkia – Wildflower. Likes sun and dry
                                                                                                               to semi-dry soils. Easy to grow and long-lasting
Plants for Southern California                                                                                 showy flowers in pink, red or purple. Attracts
A few of the many plants available to you are described below. Photog-                                         hummingbirds and butterflies.
                                                                                          © 2009 Ken Gillard
raphy is courtesy of Michael Charters at www.calflora.net
                                                                                     Deer Grass                Purple Needle Grass – Grass. Likes sun to
                                                                                                               partial sun and semi-dry soils. Hardy and showy
                                                                                                               with purple seed heads. Attracts songbirds.

                                Bush Anemone – Shrub. Likes full sun and well                                  Rose Sage –Shrub. Likes sun to partial sun and
                                drained soil. Does best with minimum care.                                     dry soil. Compact and scented with rose and
                                Produces white flowers with yellow center in                                   blue colored flowers. Attracts hummingbirds,
                                the spring. Attracts butterflies and birds.                                    songbirds, butterflies, bees and lizards.
                                                                                          © 2009 Ken Gillard
     © 2009 Ken Gillard
                                California Buckwheat – Groundcover. Likes sun                                  White Sage – Shrub. Likes sun to partial sun and
                                                                                     Rose Sage
                                to partial sun and dry to semi-dry soils. Hardy                                dry soils. Flower stalks are long and arching
Bush Anemone
                                and shrubby with tiny pink and white flowers.                                  with white flowers. Attracts butterflies, bees,
                                Attracts butterflies, bees and birds.                                          birds, lizards and nectar-loving insects.

                                California Lilac “Concha” - Shrub. Fragrant with                               Woolly Blue Curls – Shrub. Likes sun to partial
                                bright blue flowers. Likes semi-dry soil, grows to                             sun and dry soils. Native to Santa Monica
                                be 6-8’ tall. Attracts hummingbirds.                                           Mountains and requires no water in the sum-
                                                                                                               mer. Blue and pink woolly flowers bloom in
     © 2009 Ken Gillard         California Poppy – Annual Wildflower. Likes full          © 2009 Ken Gillard   the spring and fall. Attracts hummingbirds and
California Buckwheat
                                sun and dry to semi-dry soils. Thrives every-        Woolly Blue Curls         butterflies.
         Rainwater Harvesting Program                                                                                                                          11
Build a Garden
                                        Use the following steps as a guide for building a
                                        rain garden:
                                        Step 1: Outline the rain garden area with string
                                        and stakes.
                                        Step 2: If the soil is too hard to dig, moisten it
                                        with a garden hose. Allow the water to seep in
                                        overnight. Dig up existing grass and plants. Set
                                        aside any native plants that can be used in the
                                        garden.
                                        Step 3: Dig the rain garden 18 inches deep.
                                        Frame the rain garden with the sides sloped
Steps 1-2                               to about 20%. To minimize the risk of erosion,
                                        consider lining the side slopes with stones or
                                        plant vegetation. If the rain garden is on a
                                        slight slope, add a berm on the downhill slope       Step 4
                                        to hold in rainwater.
                                        Step 4: Plant the rain garden. Use a variety of
                                        species. After planting, add compost to provide
                                        nutrients to the plants. Compost or soil amend-
                                        ments can be purchased at most garden supply
                                        stores. The City of Los Angeles offers free
                                        compost at the Griffith Park Composting Facil-
                                        ity. Call (323) 913-4166 for further information.




Step 3

         Rainwater Harvesting Program                                                                 12
Other Rainwater Harvesting Options
                               In addition to rain barrels and rain gardens,         infiltrate runoff. Terraced infiltration basins can
                               additional rainwater harvesting features can          be formed on sloped properties.
                               be installed at a residential property. Visit local
                                                                                     Impervious walkways and driveways can be
                               demonstration gardens, take a workshop, and
                                                                                     removed and replaced with permeable paving
                               review references provided in the Additional
                                                                                     such as “pavers”. Pavers are brick-like materials
                               Resources section of this “How-To” Guide to
                                                                                     that are manufactured in a variety of shapes.
                               gather ideas. Consider consulting a contractor
                                                                                     Pavers fit together like tiles and are set with
                               or a landscape designer to address site specific
                                                                                     small gaps between them creating grooves for
                               needs. Some noteworthy rainwater harvesting
                                                                                     water to infiltrate the soil below. Other materi-
                               applications include installation of dry wells
                                                                                     als such as broken pieces of recycled concrete
                               (also known as French drains) or infiltration
                                                                                     can also be used. Paved walkways can also be
                               basins, and replacing paved surfaces with
                                                                                     removed and replaced with gravel or mulch.
                               permeable paving.
                                                                                     Regardless which option you choose, the
                               A dry well is a trench or basin completely filled
                                                                                     primary goal of any rainwater harvesting strat-
                               with coarse media, such as angular gravel, to
                                                                                     egy is to redirect water into the ground or a
                               create a porous layer for infiltrating runoff. Dry
                                                                                     holding tank before it reaches the storm drains.
                               wells are suitable for foot-traffic, and are typi-
                                                                                     Imagine a property as a “mini-watershed”, the
                               cally placed between a driveway or patio and a
                                                                                     principal objective is to completely eliminate
                               vegetated area, where runoff from the paved
                                                                                     runoff from leaving the property boundaries.
                               surfaces is used to soak deep into the roots of
                                                                                     These strategies and ideas will assist in recharg-
                               adjacent plants. Dry wells are not suitable for
                                                                                     ing the groundwater in a drought ridden state
                               areas that would generate sediment or silt-
                                                                                     and filtering harmful pollutants from the water-
                               laden runoff.
                                                                                     ways.
                               A rain garden is a type of infiltration basin.
                               There are several additional infiltration basin
                               designs that can accommodate existing con-
                               tours and vegetation on your property. For
                               instance depressions extending beyond the
                               canopy of a tree can be created to catch and

Rainwater Harvesting Program                                                                                                         13
Rainwater Harvesting System Maintenance
                               Perform the following activities to maintain
                               your rainwater harvesting system:
                               Rain Gutters
                               • Clean gutters at least twice a year, and more    • Check and clear downspout elbows, rain
                                 often if you have overhanging trees.               barrel screening, and overflow to prevent
                               • Make sure gutters are pitched to direct water      clogging.
                                 to downspouts.                                   • Repair any leaks and holes.
                               • Repair leaks and holes.                          • Make sure the rain barrel remains securely
                               • Look for low spots or sagging areas along the      screened to prevent mosquito entry.
                                 gutter line, and repair with spikes or place     • Inspect overflow area to make sure that
                                 new hangers as needed.                             water will continue to drain away from
                               Downspouts                                           structures and does not flow onto pavement,
                               • Check and clear elbows or bends in down-           sidewalks or neighboring properties.
                                 spouts to prevent clogging.                      Rain Gardens (or other landscaping)
                               • Repair any leaks and holes.                      • Irrigate deeply once a week during dry
                               • Each elbow or section of the downspout             months to encourage root growth and keep
                                 should funnel into the one below it. All parts     plants strong, especially while plants are
                                 should be securely fastened together with          getting established.
                                 sheet metal screws.                              • Maintain the garden regularly.
                               Rain Barrels                                       • Inspect your garden after a heavy rain.
                               • Make sure all parts are securely fastened          Remove sediment and debris, watch for ero-
                                 together and the rain barrel is securely           sion, and replace plants as needed.
                                 fastened to the building.                        • If a plant isn’t surviving in one area, try mov-
                               • Clean out the rain barrel and check for leaks      ing it to another.
                                 at least once a year.




Rainwater Harvesting Program                                                                                                      14
Where Can I Get More Information?
Help can be acquired from several sources. Start with the City of
Culver City Rainwater Harvesting Program. Explore other resources
including local organizations that provide help and information about
rain gardens and the use of native plants.
The City of Culver City                                                 Glossary of Terms
The City of Culver City Rainwater Harvesting Pilot Program
                                                                        Berm – A mound of earth used to retain water, such as along the down-
CCrainwater.ballonawatershed.org
                                                                        slope side of a rain garden
rainwater@santamonicabay.org
                                                                        Downspout – Pipe that directs stormwater runoff from the roof of a
Culver City Department of Public Works, Environmental Programs          house to the ground.
http://www.culvercity.org/Government/PublicWorks/Environmental-
Programs.aspx                                                           Impervious – Not allowing water to penetrate. Examples of impervious
                                                                        surfaces include paved driveways, walkways, or roofs.
Additional Resources
                                                                        Pervious – Allowing water to penetrate. Examples of pervious surfaces
California Invasive Plant Council                                       include flower beds and rain gardens.
http://www.cal-ipc.org/
                                                                        Rain Garden -A planted depression that allows rainwater runoff from
Native Plant Nurseries and Local Botanic Gardens                        impervious urban areas like roofs, driveways, walkways and compacted
http://lasmmcnps.org/nativenurseries.html                               lawn areas to be absorbed into the earth.
Green Garden Group (G3)                                                 Rain gutter – Captures and redirects stormwater runoff from the roof to
http://www.greengardensgroup.com/                                       a downspout. (Figure 3)
Metro Blooms (Rain garden installation video and information)           Runoff – Water that does not soak into the ground and flows over
http://metroblooms.org/index.php                                        impervious areas or areas already saturated with water. In the City of
The Surfrider Foundation Ocean Friendly Gardens                         Culver City runoff from storm events flows into the ocean without being
http://www.surfrider.org/ofg.asp                                        treated.
TreePeople                                                              Swale – A shallow ditch, usually lined with river cobble or vegetation to
http://www.treepeople.org/                                              prevent erosion, which conveys runoff to a certain location, such as a
        Rainwater Harvesting Program                                                                                                            15
Santa Monica CA Rainwater Harvesting Manual

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Santa Monica CA Rainwater Harvesting Manual

  • 2. City of Culver City Rainwater Harvesting Program Table of Contents Introduction .....................................................................................1 Before you Begin ...................................................................................9 Background ........................................................................................... 1 Assess Potential Sites ............................................................................9 What is Rainwater Harvesting? .............................................................1 Design .................................................................................................... 9 Who Should Use this Manual? ..............................................................1 Perform a Soils Infiltration Test .............................................................10 Why Harvest Rainwater? ..................................................................2 Calculate Runoff and Rain Garden Size..................................................10 To Protect Our Bays and Ocean .............................................................2 Direct Water Flow..................................................................................10 To Reduce Energy Demands ..................................................................2 Choose your Plants ................................................................................10 To Practice Water Conservation ............................................................2 Plants for Southern California ...............................................................11 To Recharge Groundwater Supplies.......................................................2 Build your Garden .................................................................................12 Overview of Rainwater Harvesting ...................................................2 Other Rainwater Harvesting Options ................................................13 Redirection Options...............................................................................2 Rainwater Harvesting System Maintenance ......................................14 What is a Rain Barrel? ...........................................................................2 Rain Gutters ........................................................................................... 14 What is a Rain Garden? .........................................................................3 Downspouts .......................................................................................... 14 How to Harvest Rainwater on Your Own ...........................................4 Rain Barrels ........................................................................................... 14 Assess your Site .....................................................................................4 Rain Gardens ......................................................................................... 14 Redirection Criteria Checklist and Safety Considerations ......................4 Where Can I Get More Information? .................................................15 How to Measure a Slope .......................................................................4 The City of Culver City ...........................................................................15 How to Redirect a Downspout to a Pervious Area .............................5 Additional Resources .............................................................................15 Before you Begin ...................................................................................5 Glossary of Terms ..................................................................................15 Redirection Procedure ...........................................................................6 How to Redirect a Downspout to a Rain Barrel .................................7 Before you Begin ...................................................................................7 Redirection Procedure ...........................................................................8 How to Build a Rain Garden ..............................................................9 Rainwater Harvesting Program i
  • 3. Introduction impervious surface such as a sidewalk, driveway or parking lot. Background Rainwater harvesting is the process of inter- The City of Culver City Rainwater Harvesting cepting rainwater from a roof (or other surface) Program is designed to help homeowners learn and putting it to beneficial use. By implement- to capture rainwater for beneficial use, and ing the harvesting techniques in this guide, reduce the amount of rainwater flowing from homeowners gain an extra water supply while their roofs into the storm drain system. The simultaneously reducing the pressure on our Program calls for disconnecting downspouts limited water supplies. that discharge to impervious areas and redirect- ing them to areas where rainwater can perco- Who Should Use this Manual? late into the soil, or collect into rain barrels. This guidance manual will help homeowners Due to heavy groundwater usage in Southern implement the first steps of harvesting rainwa- California, approximately 3.2 million-acre feet ter. It contains “How-to” information for the of space are available for groundwater re- homeowner interested in disconnecting down- charge. That is equal to 12,000 Rose Bowls filled spouts to capture and use rainwater. By follow- to the top with water. A recent study described ing the step-by-step instructions homeowners soil conditions in most of the Southern Cali- can: (1) disconnect existing downspouts; (2) fornia region as highly permeable, allowing for extend downspouts to areas that can infiltrate rapid infiltration into groundwater basins1. The rainwater; (3) install a rain barrel; and (4) rainwater harvesting process described in this construct a rain garden or other infiltration “How-To” Guide will help increase local water mechanism. Homeowners looking to imple- resources by promoting groundwater recharge. ment additional rainwater harvesting methods, or seeking supplemantal “How-to” or trouble- What is Rainwater Harvesting? shooting information should refer to Additional Many residential and commercial properties Resources provided in this guide. The program in the City of Culver City are fitted with down- website (CCrainwater.ballonawatershed.org) spouts. When it rains, water runs off roofs, will be updated with useful information as well. through these downspouts and usually onto an 1 Natural Resource Defense Council Technical Report. A Clear Blue Future: How Greening California Cities Can Address Water Resources and Climate Challenges in the 21st Century. August © 2009 G3LA 2009. Rainwater Harvesting Program 1
  • 4. Why Harvest Rainwater? Using rainwater to water plants helps conserve dwindling drinking water supplies. To Protect Our Bays and Ocean When rainwater flows from a downspout onto To Recharge Groundwater Supplies our sidewalks, driveways and streets, it collects Approximately 40% of Southern California’s a variety of pollutants. By capturing rainwater drinking water comes from groundwater. that falls on roofs, landowners help reduce the Harvesting rainwater and allowing it to infiltrate amount of runoff ultimately reaching the Santa into the ground replenishes our groundwater Monica Bay, and thus aid in improving the qual- supplies. ity of our local surface waters. Overview of Rainwater Harvesting To Reduce Energy Demands Redirection Options The State of California Energy Commission The City suggests redirecting stormwater runoff reported that water-related energy consump- from downspouts to either a rain barrel or an tion in California accounts for nearly 20% of the on-site pervious area such as a flower bed or State’s electricity, 30% of its natural gas, and rain garden as “first-steps” in the rainwater requires about 88 billion gallons of diesel fuel harvesting process. There are many more every year 2. One inch of rain falling on 1,000 features that can be implemented on a residen- square feet of rooftop produces more than 600 tial property to capture and utilize rainwater. gallons of water. If homeowners replaced this Please refer to the Sections: Other Rainwater amount of potable water with captured rain Harvesting Options and Additional Resources water, energy consumption in the State should for more rainwater harvesting ideas. be reduced. What is a Rain Barrel? To Practice Water Conservation Rain barrels store rainwater from roofs for California has entered an era of increasing reuse in landscape irrigation. Rain barrels water scarcity, coupled with projections of are containers typically made of a heavy duty increased temperatures up to 10 degrees plastic and can range in size from the standard Fahrenheit by the end of this century.2 55 gallons to more than 80 gallons. Eco-friendly 2 The State of California Energy Commission. California’s rain barrels assembled from recycled food bar- Water-Energy Relationship Final Staff Report. November 2005. rels or manufactured from recycled plastics are (http://www.energy.ca.gov/2005publications/CEC-700-2005- 011/CEC-700-2005-011-SF.PDF) available to consumers. Rainwater Harvesting Program 2
  • 5. Key components of a rain barrel include the • Rain barrels must be accessible for periodic following: cleaning. • A screen to keep debris and mosquitoes out Information on where to purchase a rain bar- • A spigot rel and rain barrel pricing can be found on the • An overflow City’s website at: • A connector for linking multiple rain barrels CCrainwater.ballonawatershed.org (if desired). What is a Rain Garden? Rain barrels are typically placed below down- spouts and must meet the following require- Homeowners can maximize both environmen- ments: tal and economic benefits by installing a rain garden in place of a grassy or impervious area. • Rain barrels should not allow UV light pen- A rain garden is a shallow depression that cap- etration in order to prevent algae growth; tures rainwater and allows it to soak into the • Rain barrels must be covered and any open- ground. Plants help to filter harmful pollutants ings must be screened to prevent mosquito in the the rainwater as it moves through the soil breeding; and layer. A rain garden is most often planted with Downspout native species creating a natural ecosystem on properties where birds, butterflies, and benefi- Swale Overflow Screen Valve cial insects thrive. Rain gardens also capture sediments carried by rainwater, preventing them from clogging the stormdrains. Barrel Spigot Multi-barrel Connector A swale directs water from the downspout to the rain garden. Many swales use rocks that A typical rain barrel set up create a dry creek bed look. Rainwater Harvesting Program 3
  • 6. How to Harvest Rainwater As a guideline, locate downspouts: on Your Own • At least 3 feet away from public sidewalks; • At least 5 feet away from property lines; Assess Your Site • At least 5 feet away from house foundations 300 ft2 Preparing a site sketch will help to determine and crawl spaces, assuring at least a 2% slope downspouts to disconnect. Begin by drawing away from the home; an outline of the home from a bird’s eye view. • At least 6 feet away from basement walls. Walk the perimeter and mark the location of Downspouts all downspouts on your sketch. Note which How to measure a slope: downspouts are connected to rain gutters; Tie a level string to two stakes pounded into the these downspouts are candidates for discon- ground. Make certain that the string attached nection. Draw in roof lines, and estimate the to the uphill stake is at ground level. Measure Figure 1: Example sketch of site square footage of the roof area (Figure 1). the distance between the stakes. This is consid- ered the width. Measure the distance from the Example of Roof Area Calculation: Redirection Criteria Checklist and Safety string on the downhill stake to the ground. This Lr = 25 ft Lt = 10 ft Considerations is the height. Make certain that the height and It is suggested that the following list of condi- width are the same units. Divide the height by Wr, Wt = 10 ft tions are met in order to safely redirect a down- the width to get the slope. Multiply this by 100 spout from a roof to a pervious area without to obtain the percent slope. (Figure 2) Roof Area = (Lr x Wr) + 1/2(Lt x Wt) = damaging building foundations, or flooding a 250 (square feet) + 50 (square feet) = basement or neighboring properties. 300 (square feet) As a guideline, direct downspouts: Height ÷ Width = Y • To gently sloped areas (preferably 10% slopes Example of Slope Calculation: Downhill Y x 100= % slope Uphill or less – See How to measure a slope); Stake Stake • To areas sloping away from buildings; Height = 6 inches = 0.5 feet Width 10’ • To rain gardens (See How to Build a Rain Width = 10 feet String Garden); 0.5 feet ÷10 feet= 0.05 • Never above septic tanks; Height 6” • Never to areas that experience ponding; 0.05 ×100 = 5% Slope • Never to fill areas. Figure 2: How to measure a slope Rainwater Harvesting Program 4
  • 7. How to Redirect a Downspout to a Pervious Area Before you Begin Prepare all of the tools and materials that you need. It is best to use Hacksaw Tin snips durable, gutter-grade materials, such as ABS Schedule 40 plastic options. Drill Bracket Other materials such as corrugated black plastic, PVC pipe, or dryer hose can be used but tend to be less durable. Consult a home and garden specialist when purchasing materials for further assistance. See the list below and Figure 3 for tools and materials you will need. Be sure to Screw driver Needle-nose Tape measure wear safety glasses. Elbow pliers Downspout extension Tools: Materials: Sheet metal Safety glasses • Hacksaw • Downspout Splash screws • Tin snips extension guard • Drill • Sheet metal screws • Needle-nose pliers • Elbow Figure 3: Materials and tools for redirecting the downspout or crimpers • Bracket • Tape measure • Splash guard Gutter • Screwdriver or nut driver • Safety glasses Downspout Select downspouts to disconnect that are connected to a rain gutter (Figure 4). Some homes in the City of Culver City are not fitted with rain gutters. If a home does not have rain gutters along the perimeter of the Extension roof, homeowners might consider installing them. This guidance manual does not provide information on how to install rain gutters because these tasks involve roof seals and require professional expertise. Figure 4: Rain gutter and downspout Rainwater Harvesting Program 5
  • 8. Redirection Procedure Redirecting a downspout to a pervious area is a simple procedure. Step 1: Mark approximately 12 inches from the ground to the downspout. This height should work for up to a 6 foot extension. Cut the downspout higher for longer extensions. 12” Step 2: Using a hacksaw, cut the downspout No basement at the mark. Remove the cut piece. You may extension 2’ need tin snips to smooth the material. Step 3: Attach the elbow over downspout. If Basement extension 6’ the elbow does not fit over the downspout, use crimpers or needle-nose pliers to crimp the Steps 1-2 ends of the cut downspout and slide it inside Step 4 the elbow. Attach the elbow to the downspout with screws; it might help to pre-drill holes. For additional stability, consider securing the elbow to the building with a bracket. Step 4: Measure and cut the downspout exten- sion to the desired length. Attach the extension to the elbow by slipping the extension over the end of the elbow. Step 5: Use screws to attach the extension to the elbow; it might help to pre-drill holes. For additional stability consider resting the extension on a support like a cinder block. To prevent erosion, place a splash guard at the end of the downspout or direct the extension to a Step 3 swale. Step 5 Rainwater Harvesting Program 6
  • 9. How to Redirect a Downspout to a Rain Barrel Before you Begin Make a list of the tools and materials needed. The installation of a rain barrel requires materials for the downspout disconnection, and materi- als to build a platform that the barrel can sit on, such as wood or cinder blocks. Homeowners may also need an additional strap to secure the barrel. Be sure to wear safety glasses. Tools: Materials: • Hacksaw • Downspout • Tin snips extension • Drill • Sheet metal screws • Needle-nose pliers • Elbow or crimpers • Bracket • Tape measure • Splash guard • Screwdriver or nut • Wood/cinder blocks driver • Securing strap • Level • Safety glasses You can transfer water from the rain barrel to a garden by filling a water- ing can, connecting a garden hose, or installing a manual drip irrigation system. Water pressure at the rain barrel spigot will depend on the level of the water in the rain barrel. The higher the water level, the greater the amount of pressure. You can also improve flow through a hose at- tached at the rain barrel spigot by elevating the barrel. Rainwater Harvesting Program 7
  • 10. Redirection Procedure Redirecting a downspout to a rain barrel is a relatively simple procedure. Elbow Step 1: Decide where to locate a rain barrel. The best place is either directly under or a few feet from the disconnected downspout. By attaching a hose to the spigot, a homeowner Measure Securing can transport water from the barrel to another strap area of the yard. Step 2: Estimate how high the barrel will rest under the downspout. Be sure to include the height of the cinder blocks or platform for the Wood / cinder blocks barrel. Mark where the downspout will be cut. Make sure to make your cut just high enough Steps 1-3 above the rain barrel to accommodate attach- ing an elbow. Hacksaw Tin snips Drill Step 3: Cut the downspout with a hacksaw so that the elbow will be inserted just above the rain barrel inlet. You may need tin snips to smooth the material. Needle-nose pliers Tape measure Step 4: Assemble the rain barrel platform. Make sure it is level. Sheet metal screws Screwdriver Step 5: Attach the elbow over the downspout with a screw. Secure the downspout to the house with the bracket. Level Safety glasses Step 6: Place the barrel beneath the elbow, making certain that the barrel overflow valve is Figure 5: Materials and tools needed for positioned in an appropriate location and away installing a rain barrel from the home. Secure the barrel to the house Steps 4-6 with a strap. Rainwater Harvesting Program 8
  • 11. How to Build a Rain Garden Assess Potential Rain Garden Sites Locate rain gardens where they can intercept Before you Begin and collect roof runoff. Potential rain garden Design and build a rain garden before discon- sites are down slope of a downspout, or adja- necting a downspout. Helpful video instruc- cent to an impervious surface. The following tions for installing a rain garden are available by factors must be considered when siting a rain Metro Blooms at www.metroblooms.org. The garden: construction of a rain garden will potentially • Build a rain garden in a relatively flat area. result in the redistribution of soil on a property. • Build a rain garden in a naturally low lying As a consequence, underground utilities are a area with good drainage. concern. Before digging, call 1-800-227-2600 to • Remove grass or paved surfaces to create acquire the location of potential underground space for a rain garden. utilities. If a project does require the redistribu- • Do not site rain gardens underneath the tion of soil it may be possible to contour the canopy of existing trees. dirt into berms or terraces designed to slow © 2009 Central Ohio Rain Garden Initiative • Do not site rain gardens above septic the flow of water. Additionally, the formation systems. of shallow depressions on the upflow side of A rain garden in bloom • Do not site a rain garden where potential the berms may trap water altogether allowing overflow will run onto neighboring the opportunity for it to infiltrate into the soil. 1. Perform a simple soils infiltration test to properties. Constructing a rain garden may be an issue if calculate the drainage rate of the potential you live on a designated landslide or hillside As a guideline, site the edge of a rain garden: rain garden site. area. Visit the Navigate LA website for a hillside • At least 3 feet away from public sidewalks; 2. Calculate the rainfall that will run off the area map or the Zone Information and Map Ac- • At least 5 feet away from property lines; portion of the roof that will be directed to cess System (Z1 MAS) websites for area maps. • At least 5 feet away from house foundations, the rain garden. Permits are not required for typical residential assuring at least a 2% slope away from the 3. Use the example calculations to estimate the landscaping projects. If you plan on making home. size of your rain garden. major landscaping modifications such as mov- Design The rain garden sizing methodology is helpful ing more than 50 cubic yards of soil or altering for maximizing the volume of runoff captured Size your garden: It is easy to size a rain garden 1 acre or more, contact the Culver City Building from a typical storm event. However, rain gar- to capture a common 3/4” storm event. and Safety Department at (310) 253-5780 for dens smaller than the calculated size, or with There are three key elements which are dis- further assistance. slow infiltration, can also make a difference. cussed in depth on the next page: Rainwater Harvesting Program 9
  • 12. Remember, you should always incorporate Calculate Runoff and Rain Garden Size Direct water flow an overflow in your rain garden such that any Step 4: Estimate the total roof area (RA) that A splash guard, followed by a grassed channel excess water, from larger storm events, will will drain to your potential rain garden. Note or swale, directs water from the end of a down- flow into another infiltration area, or to the that rooftop runoff from multiple downspouts spout extension to the rain garden site (Page storm drain system and away from the home’s can be used to support one rain garden. 3). Make sure that the swale is lined with an foundation or neighboring property. [RA = ___ (square feet)] impermeable material, such as a geotextile, if it located in the vicinity of buildings. To prevent Perform a Soils Infiltration Test Step 5: Multiply the roof area by a factor of 0.65 to determine the volume of rooftop runoff erosion and create a dry creek bed look, add The following is a list of tools and materials you that will flow to your rain garden. different sized river rocks to the swale. When will need to conduct a soils test: [V = RA x 0.65 = ___ (gallons)] the rain garden is filled with water and begins • Measuring tape to overflow, direct excess water flows away • Garden spade Step 6: Plug the numbers into the equation from buildings and neighboring properties. • Empty gallon container below to determine the required size of the rain • A watch garden. If the calculated rain garden size is too Choose your plants Step 1: Dig a square hole two feet deep and big for the property, improve drainage by the There are a variety of plants that can be used one foot wide in the deepest section of the tilling method and recalculate the rain garden in a rain garden. Diversity in plant selection potential rain garden. This size works best for size. Smaller gardens can be installed with an will add an aesthetic quality to your garden. the equation provided in this “How-To” Guide. overflow. [(hours) x (gallons) x 0.008 = _____ Consider native and drought tolerant species square footage area of rain garden] that adjust well to seasonal rainfall patterns, Step 2: Fill the hole with water and let it drain and require minimal supplemental irrigation. If completely. Fill the hole again with 5 gallons of a rain barrel is installed, the captured water can water and monitor how fast the water drains. be used for watering plants. Record how many hours it takes to drain the hole. [T = ____ (hours)] There are several resources available for the Example: selection of rain garden plants native to South- Step 3: Consider digging more holes in the po- ern California. Native plant nursery profession- tential rain garden site to determine if drainage Optimal Area of Rain Garden: als or garden clubs can provide assistance. The is uniform. If drainage is too slow to measure, T x V x 0.008 = 26 (square feet) Rancho Santa Ana Botanic Gardens provides improve the drainage by tilling in a mixture of native plant palette lists and offers native plant Where, two-thirds sandy loam topsoil and one-third gardening workshops. Please visit their web- T = 10 (hours) compost to a depth of 18 inches. site at www.rsabg.org . Other groups include RA = 500 (square feet) V = RA x 0.65 = 325 (gallons) the Water Conservation Garden at Cuyamaca College, the California Native Plant Society, The Rainwater Harvesting Program 10
  • 13. Garden Spot (bewaterwise), the Surfrider Foundation Ocean Friendly where with brilliant orange flowers. Attracts Gardens, and the Green Garden Group (G3). See the Additional Resourc- butterflies and birds. es section for more information. Deer Grass – Grass. Likes full sun and dry to Avoid using invasive plant species in your rain garden. Lists of invasive semi-dry soil. Mixes well with wildflowers. species can be found at the California Invasive Plant Council, Southern Source of nesting materials for birds. California region website: www.cal-ipc.org . Some trees are protected © 2009 Ken Gillard Coyote Bush – Shrub. Likes full sun and dry by the City and require a special permit for removal. These include: all California Poppy soils. Hardy and fast growing. Attracts birds native Oak species, Black Walnut, California Bay, and California Syca- and butterflies. more. Contact the Culver City Department of Public Works , at (310) 253-5600 for more information. Elegant Clarkia – Wildflower. Likes sun and dry to semi-dry soils. Easy to grow and long-lasting Plants for Southern California showy flowers in pink, red or purple. Attracts A few of the many plants available to you are described below. Photog- hummingbirds and butterflies. © 2009 Ken Gillard raphy is courtesy of Michael Charters at www.calflora.net Deer Grass Purple Needle Grass – Grass. Likes sun to partial sun and semi-dry soils. Hardy and showy with purple seed heads. Attracts songbirds. Bush Anemone – Shrub. Likes full sun and well Rose Sage –Shrub. Likes sun to partial sun and drained soil. Does best with minimum care. dry soil. Compact and scented with rose and Produces white flowers with yellow center in blue colored flowers. Attracts hummingbirds, the spring. Attracts butterflies and birds. songbirds, butterflies, bees and lizards. © 2009 Ken Gillard © 2009 Ken Gillard California Buckwheat – Groundcover. Likes sun White Sage – Shrub. Likes sun to partial sun and Rose Sage to partial sun and dry to semi-dry soils. Hardy dry soils. Flower stalks are long and arching Bush Anemone and shrubby with tiny pink and white flowers. with white flowers. Attracts butterflies, bees, Attracts butterflies, bees and birds. birds, lizards and nectar-loving insects. California Lilac “Concha” - Shrub. Fragrant with Woolly Blue Curls – Shrub. Likes sun to partial bright blue flowers. Likes semi-dry soil, grows to sun and dry soils. Native to Santa Monica be 6-8’ tall. Attracts hummingbirds. Mountains and requires no water in the sum- mer. Blue and pink woolly flowers bloom in © 2009 Ken Gillard California Poppy – Annual Wildflower. Likes full © 2009 Ken Gillard the spring and fall. Attracts hummingbirds and California Buckwheat sun and dry to semi-dry soils. Thrives every- Woolly Blue Curls butterflies. Rainwater Harvesting Program 11
  • 14. Build a Garden Use the following steps as a guide for building a rain garden: Step 1: Outline the rain garden area with string and stakes. Step 2: If the soil is too hard to dig, moisten it with a garden hose. Allow the water to seep in overnight. Dig up existing grass and plants. Set aside any native plants that can be used in the garden. Step 3: Dig the rain garden 18 inches deep. Frame the rain garden with the sides sloped Steps 1-2 to about 20%. To minimize the risk of erosion, consider lining the side slopes with stones or plant vegetation. If the rain garden is on a slight slope, add a berm on the downhill slope Step 4 to hold in rainwater. Step 4: Plant the rain garden. Use a variety of species. After planting, add compost to provide nutrients to the plants. Compost or soil amend- ments can be purchased at most garden supply stores. The City of Los Angeles offers free compost at the Griffith Park Composting Facil- ity. Call (323) 913-4166 for further information. Step 3 Rainwater Harvesting Program 12
  • 15. Other Rainwater Harvesting Options In addition to rain barrels and rain gardens, infiltrate runoff. Terraced infiltration basins can additional rainwater harvesting features can be formed on sloped properties. be installed at a residential property. Visit local Impervious walkways and driveways can be demonstration gardens, take a workshop, and removed and replaced with permeable paving review references provided in the Additional such as “pavers”. Pavers are brick-like materials Resources section of this “How-To” Guide to that are manufactured in a variety of shapes. gather ideas. Consider consulting a contractor Pavers fit together like tiles and are set with or a landscape designer to address site specific small gaps between them creating grooves for needs. Some noteworthy rainwater harvesting water to infiltrate the soil below. Other materi- applications include installation of dry wells als such as broken pieces of recycled concrete (also known as French drains) or infiltration can also be used. Paved walkways can also be basins, and replacing paved surfaces with removed and replaced with gravel or mulch. permeable paving. Regardless which option you choose, the A dry well is a trench or basin completely filled primary goal of any rainwater harvesting strat- with coarse media, such as angular gravel, to egy is to redirect water into the ground or a create a porous layer for infiltrating runoff. Dry holding tank before it reaches the storm drains. wells are suitable for foot-traffic, and are typi- Imagine a property as a “mini-watershed”, the cally placed between a driveway or patio and a principal objective is to completely eliminate vegetated area, where runoff from the paved runoff from leaving the property boundaries. surfaces is used to soak deep into the roots of These strategies and ideas will assist in recharg- adjacent plants. Dry wells are not suitable for ing the groundwater in a drought ridden state areas that would generate sediment or silt- and filtering harmful pollutants from the water- laden runoff. ways. A rain garden is a type of infiltration basin. There are several additional infiltration basin designs that can accommodate existing con- tours and vegetation on your property. For instance depressions extending beyond the canopy of a tree can be created to catch and Rainwater Harvesting Program 13
  • 16. Rainwater Harvesting System Maintenance Perform the following activities to maintain your rainwater harvesting system: Rain Gutters • Clean gutters at least twice a year, and more • Check and clear downspout elbows, rain often if you have overhanging trees. barrel screening, and overflow to prevent • Make sure gutters are pitched to direct water clogging. to downspouts. • Repair any leaks and holes. • Repair leaks and holes. • Make sure the rain barrel remains securely • Look for low spots or sagging areas along the screened to prevent mosquito entry. gutter line, and repair with spikes or place • Inspect overflow area to make sure that new hangers as needed. water will continue to drain away from Downspouts structures and does not flow onto pavement, • Check and clear elbows or bends in down- sidewalks or neighboring properties. spouts to prevent clogging. Rain Gardens (or other landscaping) • Repair any leaks and holes. • Irrigate deeply once a week during dry • Each elbow or section of the downspout months to encourage root growth and keep should funnel into the one below it. All parts plants strong, especially while plants are should be securely fastened together with getting established. sheet metal screws. • Maintain the garden regularly. Rain Barrels • Inspect your garden after a heavy rain. • Make sure all parts are securely fastened Remove sediment and debris, watch for ero- together and the rain barrel is securely sion, and replace plants as needed. fastened to the building. • If a plant isn’t surviving in one area, try mov- • Clean out the rain barrel and check for leaks ing it to another. at least once a year. Rainwater Harvesting Program 14
  • 17. Where Can I Get More Information? Help can be acquired from several sources. Start with the City of Culver City Rainwater Harvesting Program. Explore other resources including local organizations that provide help and information about rain gardens and the use of native plants. The City of Culver City Glossary of Terms The City of Culver City Rainwater Harvesting Pilot Program Berm – A mound of earth used to retain water, such as along the down- CCrainwater.ballonawatershed.org slope side of a rain garden rainwater@santamonicabay.org Downspout – Pipe that directs stormwater runoff from the roof of a Culver City Department of Public Works, Environmental Programs house to the ground. http://www.culvercity.org/Government/PublicWorks/Environmental- Programs.aspx Impervious – Not allowing water to penetrate. Examples of impervious surfaces include paved driveways, walkways, or roofs. Additional Resources Pervious – Allowing water to penetrate. Examples of pervious surfaces California Invasive Plant Council include flower beds and rain gardens. http://www.cal-ipc.org/ Rain Garden -A planted depression that allows rainwater runoff from Native Plant Nurseries and Local Botanic Gardens impervious urban areas like roofs, driveways, walkways and compacted http://lasmmcnps.org/nativenurseries.html lawn areas to be absorbed into the earth. Green Garden Group (G3) Rain gutter – Captures and redirects stormwater runoff from the roof to http://www.greengardensgroup.com/ a downspout. (Figure 3) Metro Blooms (Rain garden installation video and information) Runoff – Water that does not soak into the ground and flows over http://metroblooms.org/index.php impervious areas or areas already saturated with water. In the City of The Surfrider Foundation Ocean Friendly Gardens Culver City runoff from storm events flows into the ocean without being http://www.surfrider.org/ofg.asp treated. TreePeople Swale – A shallow ditch, usually lined with river cobble or vegetation to http://www.treepeople.org/ prevent erosion, which conveys runoff to a certain location, such as a Rainwater Harvesting Program 15