Payback Period from High Tunnel Rainwater Catchment for Vegetable Crops in Urban Farming

View the project final report

Commodities

Practices

• Crop Production: high tunnels or hoop houses, water management
• Farm Business Management: budgets/cost and returns
• Sustainable Communities: urban agriculture

Being at the lowest end of the value chain, farmers need to be very careful in choosing their investment. Any information that can reduce the uncertainty will help farmers in making investment decisions. Sourcing of irrigation water is one of the crucial decisions made by farmers. Irrigation water availability is a big challenge in urban vegetable farming under high tunnels. This project was implemented between 04-01-2024 and 03-31-2026 to study the feasibility of rainwater catchment from high tunnel for use in irrigating vegetable crops in urban farming. The rainwater catchment tool installed for the project included gutters on each side of the tunnel, two 550-gallon water tanks, a solar pump, a solar rechargeable battery and a solar panel. Two water filters were installed to prevent dirt getting into the drip system used to irrigate the high tunnel. A water meter measured the gallons of water used. The tool was robust and functioned well except a minor challenge that gutters buckled under snow weight in 2025, which was fixed with minimum effort. The tool cost $4970 including the materials and labor. The single largest cost was for water tanks, $2,279.70. During the project period, a total of 86600 gallons of rainwater was collected and used for irrigating the high tunnel crops. The collected rainwater would save the farmer $1303 during the project period. Thus, the calculated payback period for the tool was 7.6 years. This payback period could be reduced if the farmer can self-install the tool, saving $1000 of labor. This could bring down the payback period to 6 years. We found this rainwater collection tool very robust and long lasting without the need for any significant repair. More than 225 visitors observed the tool during the project period, and they were impressed by the sustainable nature of it. A class was also taken for students in Horticulture Department at NC State University on this topic and they also visited the project site. In conclusion, we recommend the rainwater catchment from high tunnel using this tool wherever appropriate. 

Our hypothesis was that the rainwater catchment from high tunnel would payback the farmer in less than 3 years, and would be profitable for a small urban vegetable farmer. Currently, we have a 16’x100’ high tunnel on one of the three plots of the farm. The high tunnel does not have rainwater catchment. The approach was to install gutters on both sides of a 16'x100' high tunnel, capture the rain water from gutters into rain barrels placed at the end of the tunnels, pump the captured water to drip irrigation in the high tunnel with a solar pump, quantify the amount of water used throughout the year. In parallel, record was kept of all the materials, methods and expenses incurred in installing the rainwater catchment. Using two years’ data, payback period was calculated to understand the payback investment to the farmer. 

1. Installed gutters on both sides (lengthwise) of 16’x100’ high tunnel.
2. Put one 550 gallon water storage tank on each side of the high tunnel to capture the water from the gutters. Tanks were connected to each other with a pipe.
3. Connected a water meter to the outlet of the water storage tank supplying water to the drip system. This water meter would record the gallons of water used in watering the high tunnel.
4. To increase water pressure in the drip tapes, installed a solar pump and connected it to the water storage tank pipe supplying to the drip irrigation. A pressure regulator was also installed but later found to be not necessary.
5. Watered the crops inside the high tunnel as needed using the water collected in the storage tanks.
6. Estimated the total water used in gallons in each year of the project period. This water was 86600 gallons
7. Averaged the total water used in gallons over two years to calculate average annual gallons of water used, which was 43300 gallons.
8. Estimated the value of water used from the collection tanks. The 2024 irrigation rate for Town of Cary was $15.05 per 1000 gallons of water used. Therefore, the value of used water could be calculated as: Average annual value of water used= (43300x $15.05)/1000= $651.5
9. Calculated the total expenses in installing the rainwater catchment on the high tunnel in 2024. Total expense= cost of all materials + installation labor= $3970+$1000= $4970
10. Payback period (years)= $4970 (total expense)/$651.5= 7.6 years
11. Details of all materials used is documented in this report. Based on this detailed documentation, the rainwater catchment tool could be easily installed by a farmer.