Written by Andrew Bennett, KBFA General Advisor & Certified Irrigation Designer
Irrigation intakes face many challenges, from clogging screens to critical fish habitat and flash flood blow-outs. That’s why I got excited when I first encountered an ingenious self-cleaning intake raft called Riverscreen at Tyler Morrison’s family ranch in Wardner, in the East Kootenay.
“I’m still very happy with it,” Tyler told me recently. “Going into the third year now and all hoses and parts are holding up. It allows me to keep my pump in one place even though water levels fluctuate by 15 feet.”
Since then, I’ve seen plenty of situations where Riverscreen could be usefully applied in mountain creeks, glacial rivers, murky ponds, and everywhere in between. But I had a lot of questions about winterization, compatibility with different kinds of pumps, how “fish friendly” they really are, and what kind of custom set-ups are possible, so I gave Riverscreen a call and spoke with company rep Joe Wiethern in Kansas.
Here’s what I learned after my conversation with Joe:
Riverscreen works with a rotating screen drum mounted on a raft. A small amount of water from the pump is directed to spray jets that rotate the drum and keep the screen clean.
This intake isn’t just for irrigation, Riverscreen is also used in water treatment plants and even to pump out human and livestock sewage lagoons.
WATER DEPTH and SIZES
Most Riverscreens only need about 6″ (15 cm) of water depth and use any kind of centrifugal pump mounted on the shore with a suction line out to the raft.
Riverscreen is available in sizes from 4″ (200 gpm or less) all the way up to 12″ (1800 gpm). For larger flows, multiple Riverscreens can be used in parallel. Joe says that “with the 12″ Riverscreen model we have guys pumping up to 3500 gpm with them however they are not in a regulated fish area so they have no intake velocities to meet.”
CHANGING WATER LEVELS
The suction line is usually aluminum, to keep it lightweight, attached to the raft with a flexible rubber boot. This allows the raft to go up and down with waves and changing water levels, so long as the “suction head” is within the pump’s allowances.
(Suction head is the amount of lift the pump needs to pull against both the elevation from water level and pressure lost to friction in the suction line.)
OTHER KINDS OF PUMPS?
Many installations use a self-priming pump that still only requires the 6″ of water depth. “Push button” pumps like this automatically turn on and off with water demand, saving both energy and labour.
Other farms might want a submersible pump, either because the suction lift is too high for a centrifugal pump, or for automatic irrigation, and still others may have gravity systems, or prefer to use super high-efficiency vertical shaft turbine pumps.
Riverscreen can also be used with all these applications, but they require Riverscreen’s “gravity” model which sits the drum 30″ (75cm) below water level to make sure the intake line is completely submerged.
LONG SUCTION LINES
Some farms may need the intake to be a long way from shore, maybe to avoid important habitat, or if the near-shore water is too mucky or shallow.
So long as the suction head is low, suction lines up to 160 feet long (50m) work with the proper installation. Floats are required to support rubber slip joints that connect consecutive pieces of aluminum pipe, ensuring the full length of the suction line is either perfectly flat or angled slightly upward to the pump.
Riverscreen can be used in still water to extremely swift currents, but the ideal river speed is about 5 km/h (a brisk walk).
Faster than that and the drum can spin too fast, which aerates the water, putting air into the suction line and causing cavitation in the pump.
There are a few strategies available for very fast currents: 1) The water jets are normally used to spin the drum, but they can be repositioned to actually slow the drum down. 2) A water plough at the end of the raft can divert the current and create an eddy for the drum. 3) With two flex joints, the drum can be set up to stay at an angle to the current.
For every intake, it’s vital to ensure that fish, and especially young fry, aren’t sucked onto the screen and hurt. That’s why water speeds through screens are kept very slow: Department of Fisheries regulations mandate a maximum of 0.1 ft/s.
This study from Oregon looked at water velocities in a typical Riverscreen set-up and found them all below the fish limit.
Canadian regulations also require that screens be a minimum of “8-mesh”, that is 8-by-8 holes per square inch.
Most sprinklers can pass large particles, so 8-mesh is often fine enough for irrigation and is the standard supplied with Riverscreen. But there are many cases when a finer screen is a good idea.
For example, fine sand requires 80-mesh to filter out, and that can be a good idea if sand is wearing out your pump, nozzles, and other irrigation equipment.
Microspray and drip systems often require even finer filtration, and Riverscreen can be installed with screen down to 120-mesh. By filtering water at the source, you protect your system from wear-and-tear and reduce filter maintenance.
However, fine mesh screens also limit the flow of water to the intake, so it’s important to call the reps in Kansas to make sure the intake you get matches the water volume and quality you require.
If you’re blessed with a water source in a verdant wetland or dugout, you may find yourself tangling with extremely large quantities of grass, algae, and water weeds. The rotating drum has to rotate, so you may have to get out there now and again to hack back weeds.
WINTERIZATION and FLASH FLOODS
The Riverscreen raft and intake system are made entirely of aluminum, so two people can pick it up and carry it around. All the sizes up to 10″ can be fit with ball-and-socket quick couplers, so it’s easy to unhook the pipe and pull the raft to shore. For 12” rafts, you have to unbolt the flange.
COST and SUPPLIERS
You’re looking at a minimum of $5000 for the smallest, simplest system, and over $10,000 for larger and more “custom” intakes, plus shipping on top of that.
There is a supplier in Lethbridge (RPH Irrigation Services) and Joe says the main shop in Kansas is happy to ship directly to Canada. Joe and the others at Riverscreen are also happy to take your call and answer any questions.
If you have an Environmental Farm Plan and a bit of luck and good timing, in the past you’ve been able to get a 50% cost share (cap of $12,500) for improvements to your intake. Call your EFP planning advisor and make sure you’ve got an Irrigation Management Plan in place so you’re ready when application season (usually April) rolls around…
Many thanks to Joe Wiethern at Riverscreen for his time and insight.
Our 12″ model we have guys pumping up to 3500 gpm with them however they are not in a regulated fish area so they have no intake velocities to meet.