City of Santa Monica Office of Sustainability and the Environment 1717 4th Street, Suite 100 Santa Monica, CA 90401 Landscape Rebate: Rainwater Harvesting Rain Garden Installer Guidelines TO QUALIFY FOR THE REBATE Rainwater from the existing downspout must drain to a street or alley. Existing downspouts that empty onto your landscape or some other permeable surface do not qualify. RAIN GARDEN USE PROPER SOIL MIX. Soil mix should consist of sand, top soil, and organic compost. The soil mix should be homogenously mixed. Soil excavated from the rain garden can be used as top soil. Organic compost can be any type of decomposed, stable organic matter but must not be manure-based. CONSTRUCT A PERIMETER BERM. The rain garden must be constructed with a compact, earthen berm around the perimeter of the rain garden. The berm acts like a dam and keeps rainwater contained for better infiltration. The top of the berm should be at the same level as the point at which the downspout enters the garden. INCLUDE INLET PROTECTION. The rain garden must contain at least 2 square feet of gravel at the inlet. A gravel bed at the rain garden inlet will slow and spread the flow of water to help prevent erosion in the rain garden. USE CLIMATE-APPROPRIATE PLANTS. Rain garden plants (see Suggested Rain Garden Plants) should be planted on the rain garden s slopes and berm. The center of the rain garden, which is the lowest-lying area and will stay saturated for a relatively longer period as compared to the sides, should be planted with plants that can tolerate saturated conditions for 24 to 72 hours. Hand-watering and City-approved drip irrigation are permitted. Do not irrigate with sprinklers. DO NOT UTILIZE PLASTIC OR FABRIC. Do not line the bottom or sides of the excavation with plastic or fabric. This may clog and lead to flooding. CONSTRUCT WITH A FLAT, LEVEL BOTTOM. Level the bottom of the excavated area before filling with soil mix. MAINTAIN FOR 3 YEARS. Keep the rain garden in working condition for at least 3 years by cleaning out the inlet twice per year; removing trash/debris; and weeding and pruning plants seasonally.
Your rain garden must follow these guidelines to receive a rebate. DO use this pictorial as a resource when redirecting your downspout. DO follow the guidelines below. Construct the rain garden to the suggested design specifications stipulated in this this document for soil mix, depth of soil mix, ponding depth, placement location. Mark location of rain garden with hose or rope. Excavate the rain garden to the appropriate depth. Important: Submit 3-4 photos of the excavated rain garden before the soil mix is added. Photos should clearly illustrate (1) rain garden placement with respect to the building and landscape/yard, (2) total excavated depth and (3) surface area (footprint) of the rain garden. Using a measuring tape in the frame for depth and area calculations so that depth, width, and length, in feet, can be clearly read. Submit photos to Savewater@smgov.net. These photos will be used to verify the rain garden dimensions.
Your rain garden must follow these guidelines to receive a rebate. DO use this pictorial as a resource when redirecting your downspout. DO follow the guidelines below. Level the rain garden so the bottom is flat before backfilling with rain garden soil mix. Fill with soil mix. Soil mix should consist of equal parts sand, top soil, and organic compost. Extend downspout into the rain garden. Construct a compact, earthen berm around the perimeter of the rain garden, extend downspout into the rain garden, and install at least 2 square feet of gravel at the inlet. The top of the berm should be the same level as the inlet. Soil excavated from the rain garden can be used to construct the berm and to create soil mix. Downspout extension and inlet protection Install climate-appropriate plants that are adapted to withstand periodic wet conditions. See Suggested Rain Garden Plants for ideas. TO QUALIFY FOR THE REBATE Rainwater from the selected downspout must drain to a street or alley. Downspouts that empty onto your landscape or some other permeable surface do not qualify.
Rain Garden Depth and Area Rain gardens are designed to hold a specific volume of water, but whether yours is shallow with a large footprint, or deep with a smaller footprint, or somewhere in between depends on your site and preferences. Below are three sizing options based on a 400 sq ft of roof area, which is a typical roof area that drains to one downspout on a single-family home in Santa Monica. Choose the sizing option that works for your yard given the space available and unique site conditions such as trees, existing landscaping, existing hardscapes, and utilities. Option 1: Shallow depth, larger footprint. Footprint: 42 sq ft Total Depth: 1.5 feet Soil Depth: 1.0 foot Total Depth Ponding Depth Soil Depth Option 2: Medium depth, medium footprint. Footprint: 35 sq ft Total Depth: 2.0 feet Soil Depth: 1.5 foot Choose a shape that best suites your site. The shape does not need to reflect those depicted as long as the surface area, in sq ft, is equivalent. Your garden can be long and linear, round, rectangular, or sinuous. Be as creative as you like! Option 3: Deep depth, small footprint. Footprint: 30 sq ft Total Depth: 2.5 feet Soil Depth: 2.0 feet The rain garden sizes presented are guidelines for a rain garden that is capturing roof runoff from 400 sq ft of roof area. If you have a substantially larger roof area, please call our office for sizing assistance.
DO NOT install or approve designs that are described below. You will NOT receive a rebate if you do. To protect your foundation, retaining walls, hardscapes, existing mature trees, fences, and utilities, rain gardens are never recommended in the following locations: On slopes greater than 10% Behind retaining walls Within 3 feet of fences, sidewalks, driveways, and underground utilities In areas with severely compacted clay soils Within 10 feet of the foundation of the home or any structures More than 40 away from the downspout directed into rain garden Under the drip line of mature trees DO NOT install a rain garden without inlet protection. DO NOT install a rain garden without a level bottom. DO NOT line the bottom or sides of the rain garden. I have read and understand the contents of this document and understand what may or may not qualify the property owner to receive this Rainwater Harvest Rebate. Email signed copy to, Savewater@smgov.net Property owner signature Phone Date Installer signature Phone Date Installation Address Photographs courtesy of City of Santa Monica, Stewardship Partners, Stormwater Landscapes, and the Surfrider Foundation All rights reserved.