rainwater harvesting & irrigation

Rainwater Harvesting & Irrigation

Using Rainwater as a supplemental source of water for your landscape irrigation system

By Sean Mullarkey CID, CLIA, CIC, CGIA513.379-5780

What comes down goes around?

• Can we catch all the rain?

• Do we need all the rain?

• How can we use all the rain?

Cincinnati Weather

J an Feb Mar Apr May J un J ul Aug Sep Oct Nov Dec

Avg. High 38° 42° 54° 65° 75° 84° 86° 85° 78° 67° 54° 44°

Avg. Low 21° 24° 34° 44° 52° 61° 66° 64° 57° 44° 35° 26°

Mean 30° 34° 44° 54° 64° 72° 76° 75° 68° 56° 45° 35°

Avg. P r ecip. 2.50 2.50 4.30 3.70 4.40 3.40 4.10 3.70 3.10 2.80 3.30 3.10

Avg. 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

Average Precipitation in Cincinnati 40.9Average Evapotranspiration in Cincinnati 40.3

What is Effective Rainfall ver. Actual Rainfall?

Catch It!

How do we catch it?

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

Don’t Let It Get Away!

• Sources of Rain Water?– Landscape Areas • Detain or Retain?• Contour planting• Rain Gardens• Soil improvements

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

How to figure the Sq. Ft. of a roof

Home PWR / AWPlant Water Requirement / Available Water

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

Water needed for plantsRainTotal Available

Home Property

Bank PWR / AWPlant Water Requirement / Available Water

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0

100,000

200,000

300,000

400,000

500,000

600,000

700,000

800,000

Water needed for plantsRainTotal Available

Bank Property

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

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

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

Plant Factor

Plant type Maximum appearance

Acceptable appearance

Low maintenance

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

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

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

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

Large Underground Tank

Rain Water Storage

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

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

Amount of water needed per 100 Sq. Ft. per month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Gal/100SF

27 49 95 157 230 275 284 257 183 122 52 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

Types of irrigation for landscape Beds

• Hand Watering• Cons:– Labor cost are

very high– Need skilled

labor– Time consuming


• Automatic overhead irrigation

• Pros:– Well designed systems

eliminate waist– Very low labor needs– Large water window

(application time)– Frees up labor for other task


• Automatic overhead irrigation• Cons:– High initial expense– Mostly a shotgun approach– Blocked easily by plant

material– Inflexible to alterations– Wets foliage


Drip and low volume irrigationPros:

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


• 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

Best types of irrigation for landscape Beds

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.

Drip and low volume irrigation


• 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


• 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


• 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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rainwater harvesting & irrigation

Design

sources of rain water

supplemental source

plant factor kd

rainwater formula sf

kp x kd x kmc

roof sf

rain total available300

sources of rainwater