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'~ i 37 ~ ~ (C:rrn~se et al. , 1966) . Grass inteY+cepticm ranges frtmm 0.03 to 0.9 cm per storm (Branson et al., 1981). Infiltration is the process of water Passing thrux~Z the soil surface- ' ~ atmosphere interface. Infiltration is a surface r~il,u,r.inrr,n oC4ltrolled by surface soil horizon om~ditions. Movenwsrt of waters thraagh soil (percolation) is largely ;*+~ P*++ of those controlling infiltration. Acing the mur~re of an individual precipitation event, changes at the soil surface progressively lower infiltration rates. Raindrop impact may puddle the soil surface. Soil colloids may swell upon wetting aryl reduce the soil pore ~ ~ size. Fh~en muddy waters enter the soil, ~, ~*+~~ ~_ ~~*+*~ may further reduce soil pore size. Once the precipitation intensity (mm/hr) exceeds the infiltration rate (m~/hr), Precipitation can no longer axnpletely enter the soil. R4,;c e)ooe.SS precipitation results In sheet flow or overland flora. Tfiic type of storm runoff often ocaus on camiwrid watersheds during thurderstorms. r 'lhe most important aspect of rangeland water quality is sediment produced frffi soil erosion. ~e process of soil erosion has four interrelated determ?_*+a*+*s: 1) climate, long-term temperature and precipitation; 2) soil erodibility including infiltration, percolation and resistance to dispersion; 3) slope length and steepness; and 4) plant cover. ~ese four determinants are best i ~ ]mo4m as the Universal soil Loss Equation (USIE> , (Wisclmieier an3 S5¢ith, 1978> . Any one of the four factors can .14C1,mo values, which alone may create erosion. i Precipitation and ~**~++~ ow reooxsLs were ca[q~iled for the Bourg Mine. r„rorm, ttent ~*„~mfl ows had been x~eooxT3ed in neari~y Mann Draw (north edge of mine permit area) as well as nmoff into the PxictiTm sediment detention basins. Water yield efficiency was variable and a predictive relationship between precipitation and st*~mfl ow in Mann Draw could not be ~eterm; *+~ given the available data.