A rainwater catchment system was implemented to irrigate organic vegetables.
The water rainwater collection areas were two adjacent buildings. One building was a barn which is 55 feet x 60 feet on the north roof where the water was to be collected. The other building was a machine shed which is 25 feet x 72 feet on the south roof where water will be collected.
The main objective of the project was to demonstrate a water conservation method that saves costs and contributes to an economically viable vegetable farm.
Goal 1: Rainwater Harvester project will pay for itself in savings accumulated during ten years.
Goal 2: Rainwater Harvester project will improve the public’s identification with the farm as using sustainable practices which will result in increased sales of organic vegetables.
Goal 3: Rainwater Harvester will lead to the public feeling increasingly interconnected with nature’s systems and the development of holistic thinking about the positive impact of humans farming sustainably.
Goal 4: Rainwater Harvester systems will become better understood by the public.
Rural Water at the site of a small 1/10 an acre vegetable plot reaps significant costs. The plan is to expand the garden to encompass 1/4 acre of vegetables and begin using a plastic mulch and drip irrigation method. However, at a cost of $.02 per gallon, the 27,000 gallon estimated average monthly water requirement to irrigate a 1/4 acre would accumulate a $540 monthly water bill. During a five month growing season, the cost of water would balloon to $2,700 per year. The proposal for a rainwater collection reservoir at the farm would potentially meet all the water needs at the ¼ acre of vegetables.
The proposal for conserving rainwater would establish a collection reservoir for a 5,100 square foot area. Data on Iowa’s annual rainfall indicates that a space this size could collect more than 110,000 gallons of water per year. The liberal maximum of 135,000 gallons is the calculated need for drip irrigating of 1/4 acre of vegetables. This does not account for the reduced need for water due to soil absorption during rainfall and moisture retention beneath the four foot wide plastic mulch strip. (Therefore, this estimate potentially could satisfy the entire irrigation need during a five month growing season).
The rainwater collection areas are made up of two adjacent buildings. One building is a barn which is 55” x 60” on the north roof where the water will be collected. The other building is a machine shed which is 25 x 72 on the south roof where water will be collected. Both buildings are maintained in excellent condition. Both buildings have a new metal roofs installed in the last two years.
At the lower end of the roof, an eve spout will be installed to collect rain water and the runoff will drain into a 20,000 gallon holding tank positioned between the buildings. At the ground level, an electrical water pump will be installed that meets the irrigation requirement of 30 pounds of pressure per square inch (the average pressure standard generally used in irrigation systems less than one acre). The water catchment system and resevoir will be used to irrigate the 1/4 acre of organic vegetables.
The logistics for implementing such a large water collection area was a challenge. Several of the identifying factors that contributed to a lack of practicalness in this project were as follows. The first is the difficulty that water conservation is confronted with during a drought. During the summer of 2012, very little rainfall was recorded. The amount was so small that the rainwater harvesting project was not able to supply the vegetable garden with the minimum requirement for water. Also, the practicality of using portable water tanks revealed itself as an obvious benefit to this project. In 2013, there was a reassessment of how I might utilize an alternative storage system that allows water to be shared with other farmers, transported down the road to additional sites, and more easily stored because the space designated for water storage would be accessible for other applications- full tanks could be moved and empty ones put in place.
Impact of Results/Outcomes
The project demonstrated how to use a large collection area that can adequately water a small garden without additional water supplementation. The project had some successes and pitfalls. The lessons learned may be useful to others who aspire to develop large rainwater collection areas.
Educational & Outreach Activities
The project attracted a lot of attention from people interested in establishing water collection system’s for irrigation. For example, New Pioneer Coop in Coralville is making plans to create a garden adjacent to their grocery store which will utilize roof space to collect water for irrigation. They have consuted with me as part of their planning process. New Pioneer Coop is benefiting from the lessons learned in this large scale demonstration.
A rainwater storage site of this magnitude looks better on paper than is does when trying to implement. The practicality of storing 20,000 gallons in one or two large tanks is less useful than having smaller tanks that can be used to port water to multiple sites. Implementing both the large holding tanks and smaller ones to port water would require additional costs that this project did not allocate.
The storage tanks would be best designed as permanent basins located beneath the ground that could last many many years. Then, a backup water system ie. well that could make use of the storage during times of water scarcity is necessary to ensure that all is not dependent on the weather. It is valuable to be able to port water to sites beyond the reach of the rainwater collection system.