An Undershot Water Wheel

Water your garden from a nearby stream with a paddle wheel pump system that you can build and install yourself.

| July/August 1983

I got my first taste of water wheels at the age of five, when my great-grandfather McDowell made me a toy paddle turbine to run under the spring-fed spigot at the back of the house. Today, some 65 years later, I've applied the principles of that early lesson to building a full-sized undershot water wheel that provides me with every drop of water I need to supply my thirsty garden throughout the entire growing season. 

My vegetable plot, you see, is quite a distance from the house and its plumbing. True, the garden is located not far from a small perennial mountain stream that forms the southern boundary of our property, but that "crick" runs a good 8 feet or so below my patch! 

Now I certainly don't have an aversion to honest work, but the drudgery of using a hand pump to fill a washtub, lugging the sloshing vessel around, and repeating this operation at least six times every time I wanted to water my garden forced me to look for a less labor-intensive means of getting the job done. Naturally, that first water wheel in my life came to mind, so I set about researching the design and operation of functional "paddle pumps" in hopes of building one at my site that'd handle my watering chores with a minimum of maintenance.  

Planning the Water Wheel

Because there was only about 4 inches of fall in the part of the stream bordering our land, an overshot wheel was out of the question. Unfortunately, I had little luck digging up specific information on undershot water wheels, so I had to use common sense—and a by-guess-and-by-golly approach—to make my project a success. 

Early in the game I decided that an all-wood wheel would be too expensive and time-consuming to assemble. So, considering the fact that an undershot design uses paddles rather than the intricate buckets of an overshot apparatus, I figured I'd search for a metal-spoked wheel about 4' or 5' in diameter and simply fasten some plywood paddles with 1'-square blades to it. 

I started by roughly calculating what I had to work with in the way of water. The creek usually runs about 2" deep at an 8' width. To create a weir that would direct the flow toward the center of the stream (thus enhancing its depth and velocity when at normal levels) but still withstand the punishment of occasional deluges, I piled rocks in the creek until the center channel was 16" wide and the water—normally—was about 8" deep, dimensions that I thought would be about right for the size of wheel I had in mind. 

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