Published Aug 4, 2011

Field Day Report: Using High Tunnels to Capture Rainwater for Irrigation

By Sally Worley

Linda and Randy Naeve greeted about 60 visitors with cold lemonade and ice cream sandwiches at their Nature Road Farm on a HOT Monday evening in July.

Linda and Randy discussed their 70-member CSA, now in it’s second season. Their customers get products brought to their door over a sixteen week season. Customers pay for only fifteen weeks and elect to take one vacation week each year to not receive a delivery.

Randy and Linda installed a deer fence that looks similar to bird netting but is a bit sturdier. It came from Deer-Resistant Landscape Nursery out of Clare, Michigan. It has been a good deer solution for the farm. The fencing was both economic and easy to install.

Nature Road Farm is home to a new 32X96 Gothic style high tunnel with roll down sides. This will allow them to extend both their spring and fall seasons.

The focus of the field day was the rainwater collection system installed on Nature Road Farm’s high tunnel. Linda, who is also an Extension agent for Iowa State University, created a rainwater catchment and reuse system along with ISU Ag Engineer Shawn Shouse as part of a Leopold Center-funded project. The first system was installed on a tunnel at ISU Armstrong Research Farm. Linda adapted the design for her tunnel.

One inch of rain creates 900 gallons of runoff for each side of the tunnel. This can cause serious drainage problems around the tunnel, creating erosion and standing water. Not only does the rainwater collection system mediate this problem, it also collects up to 1000 gallons of irrigation water per side.

Gutters were installed near the roll-down side junction. An additional 2X4 was put into place to make enough room for installation. Because the tunnel cover is comprised of plastic, care was taken to avoid sharp edges and hardware. The rainwater collection tanks are connected to a pump that sends the collected water to drip irrigation tape installed under black plastic. Linda and Randy utilized a solar panel to power their pump. The solar panel is an extremely light-weight model sold by PowerFilm Solar.

Here are ten steps Linda outlined for installing gutters on a high tunnel:

1. Determine and purchase needed parts: water tanks, gutter parts, lumber, hardware, pumps, fittings, hoses, plastic, repair tape to join plastic to tunnel to channel water into gutter, etc.

2. Determine slope for water flow (at least 6 to 8 inches drop for 96’ tunnel) This can be done with a string line.

3. Attach needed lumber (2 x 6’s) to ribs (rafters) just below the hipboard to accommodate the brackets at the lowest side.

4. Attach the gutter brackets and slip joints at the proper spacing, one gutter section at a time.

5. Build a support for the downspout drop into the tank.

6. Construct an overflow ball valve for the tank with downspout drop and downspouts.

7. With appropriate fittings and valves, use a garden hose to connect the valve spigot on the tank to a pre-pump filter/strainer and then the 115V Industrial pump.

8. Connect the pump to a power source.

9. Connect the pump to the header line in the high tunnel.

10. Connect the drip lines to the header.

Here is her supply list:

Quantity Item Approx. Cost
2 1,000 gallon water storage tanks $400
Hardware and fittings (screws, etc.) $50
21 Vinyl 10’gutters ($6.29/ea) $132
64 Vinyl gutter brackets ($2.79/ea) $179
4 Vinyl drop outlets ($8.29/ea) $33
20 Vinyl gutter slip joints ($3.29/ea) $66
2 Downspout elbows ($2.99/ea) $6
4 Downspouts ($11.99/ea) $52
2 Downspout sewer adapters ($3.29/ea) $7
12 8 foot 2” x 4” lumber ($2/ea) $24
4 End caps ($2.49/ea) $10
2 Garden hose (15’ and 50’) $32
1 80 mesh sieve (pre-pump filter) $7
1 Hose “Y” shut off $11
24 Tie plates (attach 2X4s to hip board) ($.53/ea) $13
(not included in estimate – 115V industrial pump; approx $115)
Tank Float Valves
2 13” inflatable vinyl balls $8
1 50’ roll coated #9 wire $6
Total for gutters, tanks, and float valve $1,036
Optional items for solar powered
1 12V marine battery $164
1 Charge controller $36
1 12V diaphragm pump $85
1 Set of connection lines, couplers $50
2 30 W Thinfilm Solar Panels ($260/ea) $520
Total for added solar pump and panel $855

Linda will publish a formal design for this rainwater catchment and reuse system later this fall. Look for it on our website as well as Leopold Center’s and ISU Value Added Extension’s.