Rainwater Catchment to a Gravity Fed
Pond
Jessica Ketchum
Site LocationThe
SenecaTreehouse.org
“Creating sustainable communities and learning centers which model nature to create basic human needs”
Site Location…Current Water Use Approx. 1600 gallons/week
Side-ViewThe water level must be 0.2 ft. above this line at 30 gpm and 1.3 ft. above at 85 gpm to have enough pressure head to move the water into the pond.
Side view of gutter shows 1/16” drop per 10ft.
Rain Collection Data/Calcs
Note: Catchment Area is Roof Footprint
Water (gal) Roof Area (ft2) Depth (in.) CF (in-ft2/gal) Runoff CF Safety CF
63135.6 2500 50.2 0.623 0.95 0.85
Annual Rainfall Data: 30-year Average Monthly Rainfall Seneca, SC at 50.2/year
63,135 gallons Water/Year
Frequency of SupplyTable 1. Calculated Water Supply
MonthMonthly
Avg. Rainfall (in)
Catchment Footprint (ft2) Conversion Factor
Runoff Coefficient Safety Factor
Monthly Volume
H20 (gal)
January 4.4 2500 0.623 0.95 0.85 5534
February 4.2 2500 0.623 0.95 0.85 5282
March 5.3 2500 0.623 0.95 0.85 6666
April 3.5 2500 0.623 0.95 0.85 4402
May 4.6 2500 0.623 0.95 0.85 5785
June 3.9 2500 0.623 0.95 0.85 4905
July 4.7 2500 0.623 0.95 0.85 5911
August 4.1 2500 0.623 0.95 0.85 5156
September 4 2500 0.623 0.95 0.85 5031
October 3.9 2500 0.623 0.95 0.85 4905
November 3.8 2500 0.623 0.95 0.85 4779December 3.9 2500 0.623 0.95 0.85 4905
STEADY IS GREAT!!
Roofing, Gutters and Downspouts
Dry Vs. Wet Conveyance Systems
Dry-Filled with water during a rain event or conveyance. Cons-Extra piping, difficult pipe runs
Wet-Full or partially full of water all of the time. Standing water can also create problems (mosquitos, pathogens, algal growth), freezing
Safety: Drainage of line and cleanout value installation. Also, wet system suitable when not drinking.
Calculating Friction
Using Table below to equate selecting fittings to length in pipe.
Diameter of Fitting
(in.)
90 ⁰ Standard
Elbow
45 ⁰ Standard
Elbow
Coupling-Straight
RunGate Valve
Friction Loss as Equivalent Pipe Length (ft)4 14 8 4 2.7
Quantity Fittings90⁰ 145⁰ 5
Couplings 11Gate Valve 2
Total Friction Loss (ft)
103.4
Calculating Friction Loss
C=140 for New Pipe (PVC Schedule 40)D=4.026 in (Inner Diameter)L=180 + 103.4 ft.Q=85 gpm
SC-Greenville 60-minute Duration 100-year Storm Data: 0.034 gpm/ft2
(0.034)(2500ft2)=85 gpm
Flow Rate, Q (gpm)
Head Loss (ft)
30 0.1940 0.3350 0.5060 0.7070 0.9380 1.1985 1.3390 1.48
Pond Size Considerations
Average monthly rainfall in gallons is around 5000 gallons.
5000/(conversion factor ft3 to gallon)
Approximately 15x15x3ft deep Pond Needed
Design Contributions
Manager at Clemson’s Organic Farm-(2009)
Experienced with Irrigation System Design Urban Permaculture Institute of the
Southeast Founder
Toured his home rainwaterand irrigation system.
Important System Extras Gate Value-useful for cleanout/drainage Emergency Drainage System from Pond Contours of Land to Drain Water from
Pond and irrigate land using gravity
References
http://www.dnr.sc.gov/climate/sco/Publications/max_rain_intensity.php
www.Rainwater%20Harvesting%20System%20Practitioner%20Manual.pdf
BE 322 Hydrology Note-Dr. Orwino (2014)