Rain Garden Design Principles

1. Locate at a minimum distance of 10 feet or more away from house foundations.

2. Determine the yard area available for the Rain Garden.

3. Check soil types to confirm the suitability of your soils.

4. Design to integrate with your yard's existing or future vegetation and landscaping.

5. Coordinate your plan with property lines, and do not change drainage patterns. Digging the depression should not change the drainage patterns of your property, nor should it present drainage alterations that negatively affect adjacent properties. If anything, containment of water on your land may slightly reduce water moving across the ground surface into the neighbors yards, which is usually appreciated.

6. Construction may require access by light duty earth moving equipment, such as a Bobcat, and perhaps a dump truck if spoils are to be moved offsite rather than being used in sculpting your on-site landscape.

7. We recommend planting with indigenous native vegetation although you may also consider ornamental water lilies and some other plants that may be desirable.

8. Some people reintroduce tadpoles and dragonflies; however, most insects will find their way on their own, without your help.

Design Process

1. Begin thinking about the size of the area you want to commit.

2. Field stake the boundaries; this is often best done with garden hose laid on the ground to outline the perimeter, or with wood stakes for those who can visualize and connect the staked points mentally. Roughly measure the square footage of project.

3. Consult Figure 1 design principles and Figure 2 rainwater volume calculations to better define the sizing and potential benefits of your project.

4. Adjust the size of your field-staked boundaries as necessary.

5. Calculate the excavated earth volume that is likely to be generated, and determine your on-site grading plan to accommodate these spoils or offsite hauling quantities and costs. Figure 4 is designed to help in this process.

6. Calculate total cost projections.

7. Adjust plan as necessary to accommodate your desired budget.

Rain Gardens Design and Costing Worksheet

Roof area	_______ft.2 (1)
Rainfall amount	_______ in (2)
Runoff volume	_______ft.2 (Figure 2) (3)
Rain garden volume = runoff volume	_______ft.2 (3)
Default average depth=1.25 ft. for the following
Rain garden area	_______ft.2 (Figure 3) (4)
Rain garden submerged radius	_______ft.2 (Figure 3) (5)
Rain garden overall (total) radius	_______ft.2 (Figure 3) (6)
Optional emergent (permanent pool) depth	_______ft. (7)
Optional emergent volume	_______ft.2 (Figure 4) (8)

Cost Estimating Work Sheet

Total volume=
Rain garden volume + emergent volume = (3) + (8) =	_______ft.2 (9)
Total volume = (9)/27 =	_______yd.3 (10)
Earthwork cost
% rain garden volume used in yard to make mounds, etc. =	_______% (11)
Cost = (11) X (10)yd.3 X $3.00/yd.3 =	$_______ (12)
% rain garden volume hauled away = 100 Ð (11) =	_______% (13)
Cost = (13) X (10)yd.3 X $12.50/yd.3 =	$_______ (14)
Plumbing costs
Distance from sump pump outlot to rain garden (if sump pump used)	_______ft. (15)
Distance from 1st gutter downspout to rain garden	_______ft. (16)
Distance from 2nd gutter downspout to rain garden	_______ft. (17)
Total pipe length = (15) + (16) + (17) =	_______ft. (18)
Total pipe cost = $0.75 X (18) =	$_______ (19)
Labor for hook-up (professional help = ~$150.00) =	$_______ (20)
Plant material cost
Aquatic area (>_ ft. deep) = 1/3 X 3.14 X (5)2 = (1/3 submerged area)	_______ft.2 (21)
Emergent area (0-_ ft. deep)=2/3 X 3.14 X (5)2=(2/3 submerged area)	_______ft.2 (22)
Shoreline area (3.14 X [(6)2-(5)2] =	_______ft.2 (23)
Upland area (owners option)	_______ft.2 (24)
Total plant costs	$_______ (Figure 5) (21)
Total plumbing costs = (19) + (20) =	$_______ (26)
Total earth work costs = (12) + (14) =	$_______ (27)
Subtotal (25) + (26) + (27) =	$_______ (28)
Misc. & contingencies = 0.25 X (29) =	$_______ (29)
Total Cost (28) + (29) =	$_______ (30)

How Much Water Will Be Directed into My Rain Garden?

Figure 2 is designed to allow you to determine the relationship between your roof area and your Rain Garden square footage. Perhaps an appropriate goal is that your design would be able to manage slightly over 75% of your rooftop runoff from a 2-year storm event.

Figure 2 Figure 4

Figure 3 Figure 5