CCGC Water Harvesting
From Place Based Grass Roots Groups Political Action Web
Water sources at the MLK site community garden of the Carrboro Community Gardening Coalition are being investigated. Water Harvesting information can be found here.
Contents |
[edit] Meeting Minutes
[edit] Status
- The town has given us permission to harvest water from both shed roofs.
- Plans for doing this should be submitted for review to Parks & Rec (Carrboro) before implementation.
- 3/4 of the gutters are already up, we are poised to install the rest of the system.
[edit] Water Harvesting Facts
- Surface area and rain: 1" rainfall on 1,000 sq ft. roof produces 625 gallons of water.
rainwater catchment coupled with the use of the well will produce ample supply for the garden.
- Catchment efficiency: 80% of water in an area can be captured.
[edit] Carrboro Historic Rainwater Averages
[edit] Annual
47.6" Average. During 2007 Drought year we were at 80% of average rainfall. http://www.nws.noaa.gov/oh/hic/current/drought/rah.htm
[edit] Quarterly
- Summer: June, July, August, : 12.9"
- Fall: September, October, November, : 10.3"
- Winter: December, January, February: 11.1"
- Spring: March, April, May: 12.2"
[edit] Available Surface Areas
[edit] North Shed
- West Roof: 404 Feet sq.
- East Roof: 425 Feet sq.
[edit] South Shed
- West Roof: 432 Feet sq.
- East Roof: 432 Feet sq.
[edit] Ideal Storage Capacity
A simple method of roughly estimating storage capacity popular among professional installers is to size the storage capacity to meet quarterly demand. The system is sized to meet estimated demand for a three-month period without rain.
[edit] Garden Demand
The general recommendation is to supply 1" of water per week to a garden. Depending on the weather conditions and the crops being grown, the garden may need 1.5" per week. It takes 625 gallons of water on 1000 sq.ft. to equal 1" of rain.
[edit] OCPYC
- Garden Area: 2400 sq.ft.,
- Planting area: 1200 sq.ft.
- Estimate of water needs: 750-1100 gallons per week.
- 22% of aggregate planted CCGC + OCPYC.
[edit] CCGC
- Fenced in area: 8,611 sq.ft.
- Planting area: 4,305 sq.ft. .
- Estimate of water needs: 2,690 gal. - 4,035 per week.
- 78% of aggregate planted CCGC + OCPYC
[edit] CCGC + OCPYC
Because CCGC and OCPYC are sharing watering sources calculating demand of both is useful.
- Planting area: 1200 + 4305 = 5,505 sq.ft
- 3,440 gal./week - 5,135 gal./week or 13,760 gal./season - 20,500 gal./season
- Assuming Planting area is constant throughout the year, per three month period garden demand:
- 3,440 gal./week x 12 weeks/3 months = 13,760 gal./season
- 5,135 gal./week x 12 weeks/3 months = 20,500 gal./season
[edit] Supply
[edit] Well
Approximately 1,000 gal./ week
[edit] Water Catchment
Water catchment water will be prioritized over well water for watering the garden.
[edit] North Shed
[edit] West Roof
404 sq. ft.
- For 1": Gallons per sq. ft. of area:: 404 feet sq. x .625 (gal./sq.foot) = 252.5.
- Efficiency Factor: = 252.5 gal x .8 = 202 gal.
- Harvest:
- Summer: 12.9" x 202 gal. = 2,606 gal.
- Fall: 10.3" x 202 gal. = 2080 gal.
- Winter: 11.1" x 202 gal. = 2,242 gal.
- Spring: 12.2" x 202 gal. = 2,464 gal.
- Volume from rain on planted garden area (OCPYC + CCGC) per season:
- Summer: 12.9" x (625 gal./1"/ 1000 sq.ft.) x 5505 sq.ft. 202 gal. = 44,384 gal.
- Fall: 10.3" x 202 gal. = 2080 gal.
- Winter: 11.1" x 202 gal. = 2,242 gal.
- Spring: 12.2" x 202 gal. = 2,464 gal.
| Month | Garden Demand | Irrigation Demand (GD not Rain or Well) | Q Avg. Rainfall (inches) | Rainfall collected (gallons) | End-of-Season storage | |
|---|---|---|---|---|---|---|
| Summer | 3,760 gal. -- 20,500 gal. | (20,500 gal.) - ( 3,440 gal. x 12.9") = -44,343 + 20,500 = -23,843 | 12.9" | 2,606 | ID - 2,606 | |
| Fall | GD | ID | 10.3" | 2,080 | ID - 2080 | |
| Winter | GD | ID | 11.1" | 2,242 | ID - 2,242 | |
| Spring | GD | ID | 12.2" | 2,464 | ID - 2,464 |
- Harvest during drought:
- Summer: 10.32" x 202 gal. = 2,084 gal.
- Fall: 8.24" x 202 gal. = 1,664 gal.
- Winter: 8.88" x 202 gal. = 1,794 gal.
- Spring: 9.8" x 202 gal. = 1,980 gal.
- Volume from rain on planted garden area (OCPYC + CCGC) per season (during 2007 drought year):
- Summer: 10.32" x (625 gal./1"/ 1000 sq.ft.) x 5505 sq.ft. = 35,475 gal.
- Fall: 8.24" x 202 gal. = 2080 gal.
- Winter: 8.88" x 202 gal. = 2,242 gal.
- Spring: 9.8" x 202 gal. = 2,464 gal.
| Month | Garden Demand | Irrigation Demand (GD not Rain or Well) | Q Avg. Rainfall (inches) | Rainfall collected (gallons) | End-of-Season storage | |
|---|---|---|---|---|---|---|
| Summer | 3,760 gal. -- 20,500 gal. | (20,500 gal.) - ( 3,440 gal. x 10.32") = -44,343 + 20,500 = -23,843 | 12.9" | 2,606 | ID - 2,606 | |
| Fall | GD | ID | 10.3" | 2,080 | ID - 2080 | |
| Winter | GD | ID | 11.1" | 2,242 | ID - 2,242 | |
| Spring | GD | ID | 12.2" | 2,464 | ID - 2,464 |
[edit] East Roof
425 sq. ft.
- For 1": Gallons per sq. ft. of area:: 425 feet sq. x .625 (gal./sq.foot) = 266.
- Efficiency Factor: = 266 gal x .8 = 213 gal.
- Harvest:
- Summer: 12.9" x 213 gal. = 2,748 gal.
- Fall: 10.3" x 213 gal. = 2,194 gal.
- Winter: 11.1" x 213 gal. = 2,364 gal.
- Spring: 12.2" x 213 gal. = 2,599 gal.
| Month | Garden Demand | Irrigation Demand (GD not Rain or Well) | Q Avg. Rainfall (inches) | Rainfall collected (gallons) | End-of-Season storage | |
|---|---|---|---|---|---|---|
| Summer | GD | ID | 12.9" | 2,748 | ID - 2,748 | |
| Fall | GD | ID | 10.3" | 2,194 | ID - 2,194 | |
| Winter | GD | ID | 11.1" | 2,364 | ID - 2,364 | |
| Spring | GD | ID | 12.2" | 2,599 | ID - 2,599 |
[edit] South Shed
[edit] West Roof
432 sq. ft.
- For 1": Gallons per sq. ft. of area:: 432 feet sq. x .625 (gal./sq.foot) = 270.
- Efficiency Factor: = 270 gal x .8 = 216 gal.
- Harvest:
- Summer: 12.9" x 216 gal. = 2,786 gal.
- Fall: 10.3" x 216 gal. = 2,225 gal.
- Winter: 11.1" x 216 gal. = 2,398 gal.
- Spring: 12.2" x 216 gal. = 2,635 gal.
| Month | Garden Demand | Irrigation Demand (GD not Rain or Well) | Q Avg. Rainfall (inches) | Rainfall collected (gallons) | End-of-Season storage | |
|---|---|---|---|---|---|---|
| Summer | GD | ID | 12.9" | 2,786 | ID - 2,786 | |
| Fall | GD | ID | 10.3" | 2,225 | ID - 2,225 | |
| Winter | GD | ID | 11.1" | 2,398 | ID - 2,398 | |
| Spring | GD | ID | 12.2" | 2,635 | ID - 2,635 |
[edit] East Roof
Same area as South shed's West roof
[edit] Designs
[edit] Gravity Design
- Takes advantage of the fact that water is captured from raised shed roofs to transport water to garden using gravity.
- Height is maximized by placing barrels:
- immediately below the gutters.
- Placing them Horizontally
- Barrels are interconnected with tubes coming to the lowest point of each barrel. Interconnectivity effectively provides cistern function.
- Raised storage water barrel structure has alternative trellis function.
[edit] Pump design
- Barrels are interconnected with tubes coming to the lowest point of each barrel. Interconnectivity effectively provides cistern function.
- A simple mobile solar powered bilge pump will move the water from the water catchment site to the main garden cistern and will also be used to pressurize and move the water from the main garden cistern to the garden.
[edit] Gravity Design
[edit] North Shed
[edit] West Half
- Barrels:
- Radius = 1'
- Height = 3.33'
- Volume/barrel = 10.5 cubic feet = 78.5 Gallons
- Total Capacity:
- Total Volume(x10) = 785 Gallons
- Bearing Weight:
- Weight of water/barrel = 8.33 lbs./Gallon x 78.5 Gallons = 654 lbs.
- Weight of Water & Barrel/barrel = 654 lbs. + Barrel weight
- Total weight: 10 barrels x 654 lbs. = 6,540 lbs.
- Weight per 4x4 column: 6,540 lbs. /13 = 503 lbs.
- Garden Distance
- 135' to water cans
- 170' to closest fence post
Needs:
- Barrels: 10 (R = 1', L = 3.33') 78.5 gal.
- Treated Lumber
- 6 (4" x 4" x 5') if can use existing shed posts
- 3 (4" x 4" x 4.75')
- 2 (2" x 6" x 3.75')
- 1 (2" x 6" x 4.8')
- 1 (2" x 10' x 4.2')
- 1 (2" x 10' x 4.7')
- 4 (2" x 6" x 4.7')
- 9 (2" x 6" x 6.3')
- 6 (2" x 10' x 6.3') or 6 (2" x 4' x 6.3')
[edit] Water Pressure
Water gains 1 psi of pressure for every 2.31 feet of vertical rise. At the MLK site, with barrels raised to below the height of gutters on the roof of the shed we can achieve:
5ft. * 1 psi/2.31 feet = 2 psi
- 2 psi is sufficient for irrigation using blue lined drip tape.
