Here are some tips about outlet pipes and spillways from articles by Mike Otto - Pond Boss Texas Best Pond Builder: “Some ponds can get away without an outlet pipe, but don’t run the risk. Analyze your watershed from an engineering perspective and verify. Pipes are necessary to not only rid your pond of extra water but to help with management. Pipe size is determined by the amount of water to run through it.” ‘Moving Excess Water’ –Mike Otto in Pond boss Mag: Sept Oct 2004.
“A Spillway Is A Spillway Or Is it?” M.Otto Pond Boss Mag: Nov-Dec 2004. One acre 1 inch deep contains 27,000 gallons. This will give an idea of water volume from a 10” or 12" rain on your water shed acreage (27000 x acres). The spillway needs to handle this water volume. Spillways work best when water flows wide and shallow.
“Emergency spillways are designed and engineered for an orderly exodus of big rains, torrents, floods. Before a spade of dirt is turned you should have a solid grasp where the spillway should sit, how large it should be, and where it directs excess water. Spillways can be made of concrete, earth, rock…. butt design and materials should be well thought out and engineered to the specific situation. Earth spillways should have the most gentle slope possible to allow water from the biggest rain possible to move as slowly as possible. If water gets over the dam you will likely repair or build a new dam. Dirt spillways are cheapest but expect maintenance and erosion. Heavy vegetation allows water to soak with less runoff. Best place for a spillway may not be at the end of the dam. Look for a natural spillway location and consider mechanical or concrete in the design because water is directly released where it needs to flow. Without a good spillway all good features of a pond or lake could be lost in one big rain event.“
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