We hypothesized that Figure 2 reflected best reasonable estimates of amounts of water contributed to Muddy Creek by natural causes, accounted for as base flow and spring seepage. Excess flows, or those not induced by natural causes, were considered to be operational spillage and irrigation-related seepage.
According to initial estimates based on 20-year USGS data, base flow contributed an average of 4,180 [m.sup.3][h.sup.-1] (41 cubic feet per second (cfs)) to Muddy Creek throughout the year: spring seepage, including snowmelt and runoff, added up to 4,078 [m.sup.3][h.sup.-1] (40 cfs) from early May through August.
A linear regression of sediment versus flow for flows greater than 8,155 [m.sup.3][h.sup.-1] (80 cfs) was derived for the Vaughn station (Figure 4), and results were used to estimate sediment contributions and partition estimates of sediment loads at Vaughn among annual base flow, spring seepage, farm field sources, and operational spillage (Table 1).
Recall from Table 1 that original estimates attributed 43 percent of total flow in Muddy Creek to natural sources, including base flow and spring seepage, 18 percent to farm field sources, and 39 percent to operational spillage.