2010-02-19_REPORT - C1980001 (4)

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3.0 SURFACE WATER As previously mentioned, Trout Creek is monitored for water quality at sites TR-A, TR-B, TR-C and TR-D and for flow at sites TR-a and TR-b. The following section discusses quantity and quality of surface water at the Edna Mine. 3.1 Gauging Stations ' Chart 1 shows the continuous streamflow records for Trout Creek at TR-a and TR-b. The flow measurements along Trout Creek indicate that the monitoring program is being placed on-line early enough in the year to record flow prior to the peak runoff period for each year. The ' individual data points show the monthly average flows and give some indication of the variability between mild winters (winters of less snow accumulation) and harsh winters (winters of greater snow accumulation). The streamflow during 2009 is elevated compared with previous years with a slight decline from 2008. The chart indicates that 2009 was an average/harsh winter for the past two decades. The flow record for 2009 shows a peak flow to have occurred in May. The peak flow historically occurs in either May or June. The runoff from the mine site was higher in 2009 than the majority of previous years probably due to more snowpack on the mine site and the on-set of warmer temperatures occurring later in the spring. The flow data presented in Chart 1 consists only of information derived from continuous flow records. Instantaneous flow measurements obtained between 1989 and June 1994 for TR-b are provided in Table 1. Prior to 1994, instability of the stream channel caused by a 1984 flood precluded the installation of any type of monitoring station in the vicinity of TR-b. The Stevens chart recorders were replaced with electronic streamflow recorders in April 2003. I The bridge located immediately downstream of TR-a was replaced in the fall of 2001 potentially altering the stage rating curve. Therefore, the decision was made to update the stage/discharge curves for TR-a and TR-b. Over the 2001 season, a total of nine cross-sections and associated ' velocities were measured at each cross section location. This data was used to compute a stage rating curve at each location. 1 The stage rating curve for TR-a was developed from flows ranging from 11 cfs to 145 cfs. The curve equation and r2 for the curve are as follows: y = 44.469x3.2806 where y = flow in cfs and x depth of flow; r2 = 0.98. Flows for 2009 are in accordance with the range used to develop the rating curve; therefore, the calculated flow is considered accurate. ' The stage rating curve for TR-b was developed from flows ranging from 13 cfs to 144 cfs. The curve equation and r2 for the curve are as follows: y = 65.049x2'431, where y = flow in cfs and x = depth of flow; r2 = 0.99. Flows for May of 2009 were above the 144 cfs used to develop the Page 3 ??^WwCHNGIN......