Distance from Field to Concentrated Flow or Water Body

Land lying near concentrated water flow and/or a water body has an increased risk of contributing P that enters surface waters.  A large proportion, possibly 90%, of overland flow occurs within 100 feet of a channel.  The distance of overland flow until the water reaches a stream or another water body is important, as P concentration in the flow water may be reduced due to sediment deposition, resorption of P and dilution. 

Current U.S. Environmental Protection Agency regulations for larger animal feeding operations prevent manure application within 100 feet of a direct conduit to surface waters if the land is cultivated.  The setback is 30 feet if the setback area is in perennial vegetation.  The importance of distance has not been well quantified, but the rate of reduction in runoff P risk increases with distance, probably up to about 300 feet, beyond which point distance may not be a significant consideration.