Portfolio: Redesigning A Small Stream Weir

by vitalbodies on July 15th, 2008

Portfolio: Redesigning A Small Stream Weir

“A weir is a small overflow-type dam commonly used to raise the level of a river or stream.”

The water for the water system comes from a very small creek deep in the dense old growth woods on the Oregon Coast. The water is loaded with fir needles and sediment and the flow is weak rather than strong. The current weir is a small dam that raises the water level so we can pre-screen the water before sending the water down the hill through nearly a 1/4 mile of tubing. Even with the existing screen the tubing or screen can become clogged because of all the fir needles and sediment naturally occurring in the area and water.

THE CURRENT SCREEN: Our current screen is an open-ended 6 inch diameter pipe less than 2 feet long that has been drilled with lots of holes and wrapped in a stainless steel screen. The screen is Zip-tied on each end and the Zip-tied ends of the screen are then stuffed into the open ends of the pipe. This design works well for it’s intended purpose but tends to need cleaning about 4 times a year and clogs un-expectedly every now and then. What usually ends up stopping the flow is the weir filling up with sediment and completely choking the filter.

SCREEN DESIGN GOALS: Ideally the next newly designed screen within the weir would be self cleaning or non-existent. Because of the remote location on the side of a small water fall, that might not be possible. Additionally the size, shape and amount of fir needles and the low amount of flow also tend to make designing a self cleaning filter difficult. If a self cleaning design is not possible, the next screen design should prevent clogging and be easy to clean and monitor. Additionally, adding some degree of filtration to remove dirt and sediment would be helpful providing the filters do not clog or need changing more than the screen. The design should also be such that the water flow is not slowly reduced until the screen clogs. Instead, the flow should not be reduced until the entire screen or the entire filter needs to be cleaned.

CLEANING: Cleaning the existing screen is done roughly 4 times a year. As the screen slowly clogs, water flow is slowly reduced until the screen needs to be cleaned again. Cleaning the current screen requires
removing the entire screen and pipe unit from the weir and carefully removing all the fir needles and sediment. Occasionally the pipe and screen unit need to be disassembled and thoroughly cleaned or even rebuilt with a new screen. The next screen design should be able to achieve easier cleaning and perhaps only need to be cleaned once a year.


NEW WEIR DESIGN: One idea is to build a small waterfall into the current weir. The waterfall could be a flat, contained area that the water flows over. This would allow the water to flow as a small, wide waterfall into a newly designed screen and filter box. By having the water flow in the form of a small, wide waterfall (rather than a tube) we would prevent clogging. In the diagram there is a 12 inch wide waterfall, that is seen from the side. Another even better design is to use a short run of large pipe coming from the weir to the weir filter. This would allow the Weir Filter to be completely outside of the stream bed. Large rocks can make their way down the stream bed in the rushing waters of winter. Over flow could (and should) pipe back to the stream. Ideally one should only take what water is needed and using a simple shut off like a float valve down below, stop the water from flowing down the pipe. This would leave as much water as possible to flow down the stream bed.

NEW SCREEN DESIGN: VitalBodies design idea was to buy or build a filter box. In water garden design they are often called POND SKIMMERS or WATER FALL FILTERS. This basic design is not self cleaning but is easy to clean, monitor and maintain. The design illustrated meets most all of our requirements. The filter basket would catch things like fir needles and small rocks and could easily lift out and be dumped.

“UV filtration could mean that we no longer have to use Chlorine.”

NEW POTENTIAL: Another design idea that VitalBodies proposed, is to make use of the water that is used for a micro hydro-electric generator. The power could be used to run a UV filter and what is called a UV clarifier. The UV clarifier is an underwater light that could be placed in the cistern to prevent algae and such. UV filtration could mean that we no longer have to use (or could at least use less) Chlorine Bleach to “purify” the water, much of which is used for drinking.

ADDITIONAL NOTE: VitalBodies also pointed out in our consultation that bleach, sadly, is only 6% chlorine, and the other 94% they do not have to state on the label what that is. What ever mystery 94% is, could be almost anything?

MAKING USE OF NEW POTENTIAL: To make use of this potential VitalBodies recommended that they might need to raise the low spot of the water line (tubing) that runs down the hill by moving a small section. In addition, we could have the tubing up by the waterfall be of a larger diameter for some distance, then come back down to the current diameter to increase HEAD. Since the flow of water is nearly 24 hours a day, 365 days a year, and the water has HEAD and FLOW from traveling so far down (nearly 1/4 mile) to the cistern, we could likely create enough power to make cost-efficient energy.

NOTE: Electric UV (Ultra Violet) water purification can happen with or without hydro.


Creating a new design for the weir and screen seems possible and affordable.

The new design could be allowing more water to flow down the stream bed by making simple changes to how the valves are set up like using a float valve.

As Eco Consultants,  VitalBodies promoted generating sustainable power with the system of tubing already in place or create even more power with some small modifications.

The system could easily reduce the amount of maintenance needed.

A more consistent flow of water could be achieved.

SIDE NOTES: VitalBodies used Inkscape an Open Source Vector Graphics program to create the illustrations.

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