Rain Harvesting Projects

A guide for Santa Monica’s rain harvest rebate

Table of Contents

Rebate Incentives 1

Eligibility and Procedures 2

How to Measure Roof Area 3

Downspout Redirect Rebate 4

Rain Barrel and Cistern Rebates 5

Why Rain Gardens, Rock Gardens and Dry Riverbeds 6-7

Rain Garden Rebate 8-12

Rain Garden Rebate Program Terms 8

How to Size a Rain Garden 9

How to Build a Rain Garden 10

Suggested Ponding Area Plants 11

Suggested Berm Area Plants 12

Rock Garden and Drive Riverbed Rebates 13-16

Rock Garden and Dry Riverbed Rebate Program Terms 13

How to Size a Rain Garden 14

How to Build a Rain Garden 15

How to Build a Dry Riverbed 16

Permeable Driveway Upgrade 17

Rebate Incentives

Rain Barrels and Cisterns

Up to $200 for a up to 199 gallon rain barrel

Up to $500 for a 200-499 gallon small cistern

Up to $2,000 for a 500+ gallon cistern

Rain, Rock and Dry Riverbed Garden

Up to $1,000

Permeable Driveway Rebate

Up to $2.00 per sq ft of driveway upgraded to a permeable driveway.

Downspout Redirect Device Rebate

Up to $40 for a downspout redirect

Important reminders!

• Receipt records are required for the watershed component and permeable driveway rebates.

• Rain harvesting (watershed) component rebates will be rebated up to the total provided receipt

amount or the maximum rebate amount, whichever is less.

• This is a reimbursement rebate program. New developments, new construction, major remodels

are not eligible.

• If you are also applying for the Cash for Grass rebate you must

complete a rain harvesting watershed component.

• Check out www.socalwatersmart.com to learn about additional

rebates available to help your save, including weather-based

irrigation controllers known as “Smart Controllers.”

Page 1

Eligibility

In order to qualify to participate in the Rain Harvesting Rebate Program, applicants must meet the following eligibility requirements:

1. The property must receive water utility service from the City of Santa Monica.

2. Projects installed as part of new construction, new development, or major remodels are NOT eligiblefor the rebate.

3. Properties that previously received a Rain Harvesting Rebate may be eligible if the previous rebatesreceived were not for the same roof area.

4. Property owner has signed the application form for the project.

Procedural Requirements

1. All rain harvesting (watershed) projects must comply with the standards and requirements listed in the Rebate Program Installer Checklist.

2. Submit printed or online application (www.smgov.net/water).

3. Complete an onsite pre-inspection by the City to review your project design. After the pre-inspection the City will determine if your project meets all the program requirements and will then send you an approval confirmation for you to proceed with your project. Rain barrel, cistern and downspout redirect projects do not require a pre-inspection but the applicant may still request one.

4. In compliance with the Internal Revenue Service (IRS), a completed Form W-9 is required. The customer receiving the rebate check must be the same person or business required to submit the Tax Identification Number (TIN) on the completed Form W-9.

5. All projects completed as part of the Watershed component of the Cash for Grass Rebate program must be completed within 6-months of the project approval date provided by the City. Projects under the Rain Harvest Rebate program only have no deadline. The City will complete an onsite post-inspection to confirm all the terms of the program were met and verify the post-install checklist.

6. The rebate check will be issued to the property owner unless prior written permission has been provided by the property owner. The property owner can have the rebate check issued to a tenant, or other designated person. Receipt records are required.

7. Rebate project must be maintained for a minimum of 3 years from the date of the final inspection, and requires an annual rainwater collection system inspection, using a City-provided form.

Eligibility & Procedure

Page 2

In order to harvest rain you need to know how much water falls on a particular area of your roof or catchment area and what will then flow through the nearest gutter. First you need to meas-ure the area of the roof. Google Maps is one way to do this.

Measuring your roof area

1. Locate your home in GoogleMaps (https://www.google.com/maps)

2. Use the street view button tolocate your rain gutter and theroof area that rainwater flowsto the gutter (see example on theright.

3. Return to the overhead view and se-lect “satellite view.” Zoom into yourhome and the roof area.

4. Right click on a corner and select“measure distance” on the drop downlist. Then click on the other edges ofthe roof.

5. Click back onto the original edge andit will show the area of that roof.

Calculate your rain harvest volume

1. Use the formula to determine the total gallons of rain you can capture:

Roof Area square feet (sgqft) ____ x .083 ft x 7.48 gal/ft3 = ____ (gallons)

Need Help?

There are various sources for helping determine just how much rain you can harvest. Check these links out for other ways to calculate your rain harvest potential. Or call us at 310-458-2201.

https://rainwaterharvesting.tamu.edu/calculators/

https://www.arcsa.org/page/6

Landscape Coaches

How to Measure Roof Area

Example—Step 2 Identify roof area and gutter

Example—Step 3 and 5 measure roof area

Page 3

Figure 1

To qualify for the downspout rebate you must meet the

eligibility terms:

1. The existing downspout is not already connected to a rain barrel or cistern, or other rainwater collection structure.

2. The existing downspout flow must drain directly to a street or alley. (see Figures 3 & 4)

3. The downspout redirect must be directed into a landscaped or permeable area that slopes away from the foundation, window wells, & basement wells (see Figure 1).

4. The downspout redirect must be disconnected 4 to 6 inches (see Figure 2) from the surface of the ground and a Flex Elbow (see Figure 5) used to extend the downspout directly into the landscape.

5. Downspout redirect must use erosion control such as a splash pad (see Figure 1) or a small bed of gravel (see Figure 2) at the end of the Flex elbow to dissipate flow and prevent erosion.

$40 rebate per

downspout

Figure 2

Figure 4

Figure 3

Figure 5

Downspout Redirect Terms

Page 4

Page 5

The following program terms are required to qualify for the rain

barrel and/or cistern rebates:

.1 The rain barrel and/or cistern must be connected to at least one

downspout or rain chain and the roof must have gutters.

.2 The rain barrel and/or cistern must not block or restrict access

to doors, walkways, or pathways.

.3 The rain barrel and/or cistern must be elevated at least 6 inches

above the ground (for above ground systems only) on a level

and solid foundation, such as a concrete pad, pavers, or blocks

to provide stability and increase pressure.

The rain barrel and/or cistern must have a cover and pre-

treatment to prevent mosquitos, rodents, and debris from

entering.

5. The rain barrel and/or cistern must be strapped to your home

or building for earthquake and personal safety, if the height of

the barrel/cistern is two times greater than the width.

6. The rain barrel and/or cistern must be equipped with an

overflow pipe or tube near the top of the rainwater storage

system, which is at least 1 to 3 inches in diameter and directs

overflow safely away from the foundation of adjacent

structures.

7. The rain barrel and/or cistern must be equipped with a spigot

near the bottom of the rain barrel or cistern, or must utilize a

pumping system. Cisterns that are connected to a pressurized

irrigation system require a single-trade plumbing permit from

the Building and Safety Division located at City Hall. There is no

permit fee.

The rain barrel and/or cistern must be maintained for a

minimum of 3 years.

There are many styles and design variations available for

rain barrels and cisterns. Which one will you choose to

help you save for a rainy day?

Rain Barrel & Cistern Terms

Why Should I Install a Rain or Rock Garden?

Rain that lands on compacted, pervious or impervious surfaces, and flows over the ground is called

rainwater. When rainwater leaves one’s property, it becomes a discharge and is called stormwater or

runoff. This water is regulated for quality by the state under the Clean Water Act. As stormwater

travels toward Santa Monica Bay, it picks up pollutants, such as trash, metals, oil, grease and bacteria

from streets, lawns, and parking lots, and, as a result, is a major contributor to water quality

degradation in our local waterways.

Rain from the roof (or driveway, parking lot) can easily be directed into a rain or rock garden by

extending one or more downspouts into the garden. A rain or rock garden is an excellent way to slow

that water down and to infiltrate it into the ground using that water as a resource in your yard and

preventing runoff and stormwater pollution. The City of Santa Monica offers a rebate of up to $1,000

to install a rain or rock garden in your yard.

What is a Rock Garden?

A rock garden is a shallow excavation that is filled with 1 to 3 inch diameter

rocks. Much like the rain garden, rainwater is stored in the void spaces

between the stones where it can be held for several hours before it percolates

into the soil. However, unlike the rain garden, the rock garden does not have a

ponding area or vegetation– one can walk on it.

What is a Rain Garden?

A rain garden is a shallow, planted depression filled with a loose and permeable

soil mix that is designed to collect rainwater from roof, driveway and parking lot

surfaces. The rainwater collected in the rain garden is stored temporarily in the

soil mix and surface ponding area, and then slowly seeps into surrounding soils

over several hours and days. Plants are distributed throughout the garden.

How long will it take the rain or rock garden to drain after it rains?

A rain or rock garden will be designed to drain within 24 hours, no longer than 72 hours. The type of

soil mix, size and shape of the garden will determine how quickly the collected rainwater will infiltrate

into the native soils.

Why Rain and Rock Gardens?

Page 6

What is a Dry Riverbed ?

Dry riverbeds or dry creeks are garden features that mimic the meandering landscapes often found along river

and stream beds. A dry riverbed is a kind of rock garden that slows heavy rainwater flows and minimizes erosion.

It is made up of a shallow swale that is lined with varying sizes of stones. Large stones help withstand a serious

downpour and anchor the other stones in the dry bed, slowing rainwater runoff. In a garden, the careful

placement of water-worn stones, or river slicks, along a swale can be aesthetically pleasing, providing ideal places

for select plants to grow.

Dry riverbed design tip

Often a dry riverbed is designed to flow water into an

underground infiltration basin (like a rock garden or dry well)

because unlike the rain garden, the dry riverbed does not have a

specific ponding area where water can settle and slowly seep

into the ground.

What is the difference between a dry

riverbed and a rock garden?

A rock garden is designed to concentrate infiltration in a small

focused area, and is flat and walkable. A dry riverbed is

elongated, depressed, sinuous and filled with different sized rock

and stone, making it a conduit for infiltrating water across a

landscape.

Photo courtesy of Surfrider Foundation

Why Dry Riverbeds?

Page 7

Must receive rainwater from an impervious or compacted

(effectively impervious) surface via downspout extension

or dry riverbed

1. The rain garden must be constructed with a compact, earthen berm around the perimeter of the rain garden.

2. The rain garden must contain at least 2 cubic feet of gravel at the inlet for erosion control.

3. The rain garden must be planted with climate-

appropriate plants — see the Suggested Rain Garden Plants List on pages 9-10 for plant recommendations.

4. The rain garden must be constructed with a flat, level bottom.

5. Do not install a plastic weed barrier or filter fabric. These materials are not eligible for rebate.

6. The rain garden must be constructed according to the soil mix, sizing and placement recommendations discussed during the water harvesting consultation.

7. Overflow from garden should sheet flow away from structures or flow through pipe to street or alley.

8. Rebate project must be maintained for a minimum of 3 years.

Rain Garden Terms

Page 8

Up to $1,000

rebate!

Use the chart below to determine the minimum square footage of your rain garden based on the depth of it

and the size of the roof.

Eligibility Terms

Must be a City of Santa

Monica Water customer

Must receive rainwater from

&

&

Rain Garden Area footprint, sq ft

Roof Area, sq ft

200 400 600 800 1,000 1,500 2,000 2,500 3,000

Soil

Me

dia

De

pth

(ft)

*

1 21 42 63 83 104 156 208 260 313

1.5 18 35 53 70 88 132 175 219 263

2 15 30 45 61 76 114 152 189 227

2.5 13** 27 40 53 67 100 133 167 200

3 12** 24 36 48 60 89 119 149 179

125 249 374 499 623 935 1,247 1,558 1,870

Gallons Stored within the Rain Garden * This is soil media depth and not total depth. Add 0.5 ft (ponding depth) for total depth.** Side slopes may be unstable due to small footprint.

Depth of BMP (ft.) Roof Area Diverted ft2 Min ft2 Rain Garden

1

1.5

2

2.5

3

Sizing a Rain Garden

Example Sizing of a Rain Garden

For 400 sqft of roof diverted at a 2 ft depth, you will need a 30 square feet garden, and it will capture 249

gallons.

Conversely, if you only have 50 square feet of garden space and 600 square feet of roof diverted, then you

know you need at least 2 ft of soil media.

Page 9

Choose an area of the yard that is sloping gently away from your

structure and near a downspout so it can easily be extended into

the rain garden. The downspout extension provides a way for

rainwater to travel from the roof into the rain garden.

Call Dig Alert (811) before you start your project to check on

possible pipes in project area to avoid. Begin digging the rain

garden to the depth discussed in the water harvesting

consultations. The typical depth is 12 to 18 inches. Make sure that

the bottom of the rain garden is flat and level.

Create a soil mix by mixing the excavated soil with at least 30%

compost to create better soil health and increased water

retention. If your soils are slow draining (clay), sand or pumice

should be added; this will be discussed during the rain

harvesting consultation. Fill in the rain garden with the loose soil

mix but leave a 6” depression in the center of the garden to

allow for temporary ponding. Use the excavated soil to build a

compact berm around the downhill edge of the garden, which

will act as a dam and retain water in the garden while it slowly

seeps into the soil.

Use a dry creek bed, trench drain, or pipe to extend the

downspout into the rain garden. Use at least 2 cubic feet of rock

at the inlet of the rain garden to dissipate energy and prevent

erosion. Install plants that are accustomed to drought

conditions, and do not mind saturated soil conditions on

occasion. Finally, apply a three inch layer of bark

mulch and then...save for a rainy day!

Step 1

Step 2

Step 3

Step 4

How to Build a Rain Garden

Page 10

The plants in the ponding area, which is the lowest lying part of the garden, will remain saturated for days at

a time. Because of this, you will need to install plants that can tolerate “wet-feet” in the ponding area. The

lists below are suggestions for plants that will thrive in the low-lying, ponding area.

Installation of these specific plants are not required for the rain garden rebate. Other drought-tolerant

species that are adapted to periodic wet conditions may be used as well.

Ponding Area Plants

Rain Garden Cross-Section:

Perennials and Wildflowers

• Blue Eyed grass (Sisyrinchium Spp.)*

• Coyote Mint (Mondarella villosa)*

• Douglas Iris (Iris douglasiana)*

• Sticky Monkey Flower (Mimulus aurantiacus)*

• Scarlet Monkey Flower (Mimulus cardinalis)*

• Primrose Monkey Flower (Mimulus primuloides)*

• Seep Monkey Flower (Mimulus gattatus)*

Grasses and Sedges:

• California Black-flowering Sedge (Carex nudata)*

• Santa Barbara Sedge (Carex barbarae)*

• Small Cape Rush (Chondropetalum tectorum)

• Atlas Fescue (Festuca mairei)

• California Gray Rush (Juncus patens)*

• Berkeley Sedge (Carex tumulicola/divulsa)*

* Indicates California Native

Diagram courtesy Stewardship Partners

Suggested Ponding Area Plants

Page 11

Ponding Area

Berm Area

The plants in the berm area are plants that will thrive in drier conditions.

Installation of these specific plants are not required for the rain garden rebate. Other drought-tolerant species

that are adapted to periodic wet conditions may be used as well.

Berm Area

Perennials and Wildflowers:

• Common Yarrow (Achillea millefolium)*

• Western Columbine (Aquilegia Formosa)*

• California Pipevine (Aristolochia californica)*

• Anchor Bay (Ceanothus gloriosus 'Pt. Reyes'*

• Yankee Point Ceanothus (Ceanothus griseus horizontalis)*

• Purple Sage (Salvia leucophylla)*

• Creeping Sage (Salvia sonomensis 'Bee's Bliss')

• California Fuchsia (Epilobium canum)*

• Beach Aster (Erigeron glaucus)*

• California Buckwheat (Eriogonum fasciculatum)*

• California Poppy (Eschscholzia californica)*

• Leopard Lily (Lilium pardalinum)*

• Beardtongue (Penstemon heterophyllus)*

• Autumn Sage (Salvia greggii)

Grasses and Sedges:

• Deer Grass (Muhlenbergia rigens)*

• Pink Muhly (Muhlenbergia capillaris)

• Blue Grama (Bouteloua gracillis ‘BlondAmbition’)*

• Purple Needle Grass (Stipa pulchra)*

Shrubs:

• Dwarf Coyote Brush (Baccharis pilularis‘Pigeon Point’)*

• Red-flowering Currant (Ribessanguineum)*

• White Sage (Salvia apiana)*

• Rose Sage (Salvia pachyphylla)*

• Catalina Currant (Ribes viburnifolium)*

* Indicates California Native

Learn More!

Learn more about what is a climate-

appropriate, native plant. Visit,

www.LACoastalGardens.com

Find the Right Installer!

Visit www.epa.gov/watersense/findapro

and utilize its contractor search engine or

the City’s Buy Local Santa Monica program

at, www.buylocalsm.com and search for a

local landscape designer

Suggested Berm Area Plants

Page 12

Up to $1,000

rebate!

The following terms are required to receive a rebate for a

rock garden and/or dry riverbed:

1. Must receive rainwater from an impervious or compacted (effectively impervious) surface via downspout extension

2. The rock garden or dry riverbed must be constructed according to the sizing and placement recommendations discussed during the rain harvesting consultation.

3. The rock garden must be filled with rock that is at least 1 inch diameter.

4. The rock garden must have a minimum depth of one foot

and a flat, level bottom.

5. Overflow from garden should sheet flow away from structures or flow through pipe to street or alley.

6. The rock garden or dry riverbed must be at least 3 feet from fences, driveways and all walkways.

7. The rock garden or dry riverbed must be at least 3 feet from underground utilities.

8. The rock garden or dry riverbed must not be within the drip line of any existing trees.

9. The rock garden must be maintained for a minimum of 3 years.

Rock Gardens & Dry Riverbeds Terms

Page 13

Use the chart below to determine the minimum square footage of your rock garden or dry riverbed

based on the depth of it and the size of the roof.

Must have participated in a

rain harvesting consultation

Must receive rainwater from

an impervious or compacted

(effectively impervious) surface

via downspout extension or

dry creek bed

&

& Example Sizing of a Rain Garden

For 600 sqft of roof diverted at a 2 ft depth, you need 63 sqft of rock garden (i.e. 7ft x9ft) or dry riverbed (i.e., 3ft x 21ft).

Rock Garden/Dry River Bed Area footprint, sq ft

Roof Area, sq ft

200 400 600 800 1,000 1,500 2,000 2,500 3,000

Gra

vel*

D

epth

(ft)

1 42 83 125 167 208 313 417 521 625

1.5 28 56 83 111 139 208 278 347 417

2 21 42 63 83 104 156 208 260 313

2.5 17 33 50 67 83 125 167 208 250

3 14 28 42 56 69 104 139 174 208

125 249 374 499 623 935 1,247 1,558 1,870

Gallons Stored within the Infiltrative Rock Garden/Dry River Bed

* Gravel diameter of 1" to 3" for rock garden only

Sizing Rock Gardens & Dry Riverbeds

Page 14

Depth of BMP (ft.) Roof Area Diverted ft2 Min ft2 Rock Garden Min ft2 Dry River Bed

1

1.5

2

2.5

3

Rock Garden/Dry River Bed Area, sq ft

Roof Area, sq ft

200 400 600 800 1,000 1,500 2,000 2,500 3,000

Grav

el*

Depth

(ft) 1 42 83 125 167 208 313 417 521 625

1.5 28 56 83 111 139 208 278 347 417

2 21 42 63 83 104 156 208 260 313

2.5 17 33 50 67 83 125 167 208 250

3 14 28 42 56 69 104 139 174 208

125 249 374 499 623 935 1,247 1,558 1,870

Gallons Stored within the Infiltrative Rock Garden/Dry River Bed

* Gravel diameter of 1" to 3" for rock garden only

Example Rock Garden

63 sqft

(7ft by 9 ft)

Rock Garden Cross-Section:

Choose an area of the yard that is sloping gently away from your structure.

Place the rock garden in an area that is near a downspout so that it can easily

be extended into the rock garden. The downspout extension provides a way

for rainwater to travel from the roof into the rock garden.

Use a dry creek bed or pipe to extend the downspout into the rock garden.

Now you are ready to...save for a rainy day!

Step 1

Step 2

Begin digging the rock garden to the depth discussed in the rain harvesting

consultation. The typical depth is 24 to 36 inches. Make sure that the

bottom of the rock garden is flat and level.

Step 3

Install a permeable landscape cloth over the soil before filling in with

rock. Fill in the hole with rock that is at least 1 inch diameter. Bigger rock retain more rainwater. Make sure it is level with the surrounding grade.

Step 4

How to Build a Rock Garden

Page 15

Choose an area of the yard that is sloping gently away from your structure.

Place the dry river bed in an area that is near a downspout so that it can

easily be extended into the dry creek. The downspout extension provides a

way for rainwater to travel from the roof into the dry river bed.

Begin digging the dry river bed to the depth discussed in the rain harvesting

consultation, usually between two and three feet deep, using the soil you

dig out to build up planting mounds on both sides of the creek. Using a

sinuous curving shape for your creek bed will make it look more natural.

Tamp the channel to create a firm flat surface with angled sides, Line with

a permeable landscaper cloth to reduce the chances of an impermeable

barrier created between rock and soil. Sometimes a base layer of pea

gravel is used.

Use rocks (or cobble) and boulders of different sizes and shapes, keeping in

mind the size of your creek bed and your yard. Spread the rocks over the

sides and bottom of the creek bed. Then place some of the cobble just past

the edge of the creek, creating the look of washouts. Plant the sides of the

creek with climate appropriate plant material. Now you are ready to...save

for a rainy day!

Step 1

Step 2

Step 3

Step 4

Photos in this document are courtesy of Amy Williams Photography and Urban Water Group

How to Build a Dry Riverbed

Page 16

Permeable Driveway Upgrade

Upgrade your old impermeable driveway to a new permeable driveway and get up to $2 per square foot!

Page 17

Additional Questions, Contact Us!

Email russell.ackerman@smgov.net

or call (310) 458-8405

Watershed Management Section

City of Santa Monica

Office of Sustainability and the Environment

1717 4th Street, Suite 100