Las Vegas Wash Tributaries Water Quality Report, 2003-2007

80007000All tributaries contribute 15,835 acre-feet flow annually to the Las Vegas Wash6000Average annual flow, Acre-feet500040003000200010000FW_0 LW12.1 SC_1 MC_1 DC_1 BS_1Figure 18: Overall average flow volume (acre-feet).3.2.0 Mass LoadingThe daily mass loading rates (lbs/day or tons/day) of TDS, heavy metals, and nutrients from eachtributary were calculated using the average concentrations of these chemical constituents and theaverage flow rate in each tributary. The relative percentages of the total daily load (TDL) ofeach chemical constituent from all seven tributaries vs. that in the Wash were also computed(Table 12). Flow rates and concentrations from Site LW0.8 (Wash below Lake Las Vegas,USGS site number 09419800) was used as the Wash site for the mass loading computations.Comprising approximately 8% of the Wash total flow, the tributaries together contributeapproximately 18% of total TDS, 31% of Se, 20% of arsenic, 2% of total metals, 3% of nitrogennutrient, and 1% of phosphorus nutrient mass loading to the Wash (Table 12). Duck Creek andthe Flamingo Wash are the two major sources of TDS, Metals (especially Se and arsenic) andnutrients from the tributaries to the Wash (Table 13). LW12.1 contributes the third largestoverall mass loading and the greatest mass loading of aluminum and BS_1 contributes thegreatest mass loading of iron (Table 13).Tributary Water Quality Monitoring Program, 2003-2007 30