• 25yr/24hr storm = 2.2 inches precipitation (see Montana precipitation map, source: Western Regional Climate Center, Reno, NV, http://www.wrcc.dri.edu)
• Lot area = 4.36 acres
• Unpaved animal feeding areas hold about the first 0.5 inches of precipitation. Thus storms of less than 0.5, which is the majority of the storms in this area, produce no runoff.

Equation:

RO = [(P - 0.5) ÷ 12 in./ft] x LA

Variables:

RO	= lot runoff, ac-ft
P	= Precipitation, inches
LA	= lot area, acres

RO = [(2.2 – 0.5) ÷ 12] x 4.36 ac = 0.62 ac-ft

Return to regular view	Text-only	Updated: 08/29/2006