How to design your rainwater harvesting system to work with an irrigation system,

1. Rainwater Harvesting &
Irrigation
Using Rainwater as a supplemental source of
water for your landscape irrigation system
By Sean Mullarkey CID, CLIA, CIC, CGIA
513.379-5780

2. What comes down goes around?
• Can we catch
all the rain?
• Do we need
all the rain?
• How can we
use all the
rain?

3. Cincinnati Weather
Jan Feb M ar A pr M ay Jun Jul A ug Sep Oct Nov Dec
A vg. Hi gh 38° 42° 54° 65° 75° 84° 86° 85° 78° 67° 54° 44°
A vg. Low 21° 24° 34° 44° 52° 61° 66° 64° 57° 44° 35° 26°
M ean 30° 34° 44° 54° 64° 72° 76° 75° 68° 56° 45° 35°
A vg. P r eci p. 50
2. 2. 50 4. 30 3. 70 4. 40 3. 40 4. 10 3. 70 3. 10 2. 80 3. 30 3. 10
A vg. E T 0. 62 1. 12 2. 17 3. 60 5. 27 6. 30 6. 51 5. 90 4. 20 2. 79 1. 20 0. 62
What is Effective Rainfall ver. Actual Rainfall?

5. How do we catch it?

6. Don’t Let It Get Away!
• Sources of Rain Water? “I wasn’t thinking the sky!”
– Roofs
• Least amount of pollutants
• Elevation of gutter allows directing to tank without pump
• Easy to pre-filter and provide first flush
• Low cost of conversion
– Pavement
• Dirt and pollutants are more abundant
• May need pumps to move water to storage area
• Can be expensive to convert for collecting Rain, more cost
effective if done during construction

7. Don’t Let It Get Away!
• Sources of Rain
Water?
– Landscape Areas
• Detain or Retain?
• Contour planting
• Rain Gardens
• Soil improvements

9. Site Comparison
Area Home 1” Rain Bank 1” Rain
Land SF 22700 45500
Pavement SF 900 24200
Roof SF 1200 748 gal 5800 3613 gal
Landscape/turf SF 20600 91% 15500 34%
Rainwater Formula ( SF x .623 = Gal. Collected for 1 inch rainfall)
.623 is a constant that coverts Square Feet to Gallons

10. How to figure the Sq. Ft. of a roof

11. Home PWR / AW
Plant Water Requirement / Available Water
1,200,000
Home Property
1,000,000
800,000
Water needed for plants
600,000
Rain
Total Available
400,000
200,000
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

12. Bank PWR / AW
Plant Water Requirement / Available Water
800,000
Bank Property
700,000
600,000
500,000
Water needed for plants
400,000
Rain
Total Available
300,000
200,000
100,000
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

13. What are we going to water
• What are we going to use the water for
• When will we need it.
• Where will it be located

14. How much water do our plants need?
• Practical methods , the kind you use every day
• Management methods, depends on how
much management budgets for watering
• Scientific Methods, good for developing a
base line to use along with your practical
methods

15. Plant Water Requirement (PWR)
• PWR = Landscape Coefficient X Reference ET
KL = KP x Kd x Kmc
• KL = landscape coefficient
• KP = plant factor
• Kd = vegetation density factor
• Kmc = microclimate factor

16. Plant Factor
Plant type Maximum Acceptable Low maintenance
appearance appearance
Trees 0.90-0.95 0.70-0.75 0.45-0.50
Shrubs 0.60-0.65 0.45-0.50 0.30-0.35
Desert plants 0.40-0.45 0.30-0.35 0.20-0.25
Ground covers 0.70-0.80 0.50-0.60 0.30-0.40
Mixed planting 0.90-1.00 0.75-0.80 0.50-0.55

17. Kd = vegetation density factor
Kd refers to the collective leaf area of the plants covering or shading
an area of ground
More foliage equals more transpiration hence more water is needed.

18. Kmc = microclimate factor
Plants growing is shade need less water
Plants growing next to a brick wall on the
south side of a building need more water

19. Calculating PWR
6.5”/month * .7 = 4.6
1200 SF of plantings
(1200 x 4.6) = 460CF of water
12 460 x 7.48 = 3440 Gal for month
7.48 gal per CU FT of water

20. Large Underground Tank

21. Rain Water Storage

22. Rain Water Storage

23. Rain Water Storage

24. Storage Tank Cost
MATERIAL COST, Small System COST, Large system
galvanized steel $225 for 200 gallons $950 for 2000 gallons
polyethylene $160 for 165 gallons $1100 for 1800 gallons
fiberglass $660 for 350 gallons $10,000 for 10,000 gallons
ferro-cement Price variable upon location Price variable upon location
fiberglass/steel composite $300 for 300 gallons $10,000 for 5000 gallons
aluminum Cost prohibitive for water use Cost prohibitive for water use
http://www.lid-stormwater.net/raincist_cost.htm

25. Using the Rain Water
• Most Rainwater Harvesting System are best
utilized watering landscape plantings not turf
because of the limited size of storage units
• If you have a large storage area such as a lake
all planted areas can be watered with the
stored rainwater
• Most systems will need some sort of pump to
distribute the water through a pipe net work

26. Amount of water needed per 100
Sq. Ft. per month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Gal/ 27 49 95 157 230 275 284 257 183 122 52 27
100SF

27. Types of irrigation for landscape Beds
• Hand Watering
• Pros:
– Can apply varying
amounts of water
to specific plant
– Can conserve
water resources
– Allows for visual
inspection of
plants
– Equipment cost
are low

28. Types of irrigation for landscape Beds
• Hand Watering
• Cons:
– Labor cost are
very high
– Need skilled
labor
– Time consuming

29. Types of irrigation for landscape Beds
• Automatic overhead
irrigation
• Pros:
– Well designed systems
eliminate waist
– Very low labor needs
– Large water window
(application time)
– Frees up labor for other task

30. Types of irrigation for landscape Beds
• Automatic overhead irrigation
• Cons:
– High initial expense
– Mostly a shotgun approach
– Blocked easily by plant
material
– Inflexible to alterations
– Wets foliage

31. Types of irrigation for landscape Beds
 Drip and low volume irrigation
 Pros:
 Highest potential efficient use of water
 Low labor needs
 Economical to install
 Largest water window
 Places water at or near
the roots
 Keeps foliage dry
 Low precipitation rates

32. Types of irrigation for landscape Beds
• Drip and low volume
irrigation
• Cons:
– Can be unsightly
– Easily damaged when
working in the beds
– Hard to visually inspect its
operation
– Needs clean water

33. Best types of irrigation for landscape
Beds
Drip and low volume irrigation
Most cost effective in the long
term, utilizes the ever more
precious resource of water
better than any method, will
get you LEED points , very
flexible to change, can be
unsightly if not installed
properly.

34. Best types of irrigation for landscape
Beds
• Controlling the rate of application
– Drip and low volume irrigation have very low
precipitation rates. Hand watering can be
controlled to eliminate run off as well.
• No run off
• Will not remove air from soil unless it is allowed to run
for to long of an irrigation cycle
– Over head irrigation generally has a very high
precipitation rate , so do hose end sprinklers

35. Best types of irrigation for landscape
Beds
• Low volume irrigation provides the most
advantages over the alternative methods
– Efficient use of water
– LEED qualified (GREEN)
– Waters better than most rain storms as
considered against uniformity and precipitation
rate
– Drip goes hand in hand with rain water harvesting

36. Best types of irrigation for landscape
Beds
• Rain water harvesting
– If you are using any type of cisterns to capture rain
water, drip is an Ideal way to use that water
• Need to filter the water before use
• If water is from pavements check for soluble salts and
other contaminants

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