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. . USFWS - Palisade/Grand Junction Stream Flow Analyses - DRAFT May 12, 1995 Page 6 III GAGING STATION RECORDS III.1 27.5 Road Gage Richard D. Piland and Associates (Piland) collected and interpreted streamflow data from . a Stevens recorder at the 27.5 Road Gage site during the later months of 1991 through 1994. The rating curves developed to determine the flow rates are shown in Figure 2. The following comments are provided on the rating curves used to determine the discharge. .1991-1992: Piland prepared a stage discharge relationship for the site based on current meter measurements of 707 cubic feet per second (cfs) and 1,313 cfs in 1991 and 646 cfs and 2,112 cfs in 1992. Please note that flows were experienced in 1992 that exceeded 2,112 cfs which may affect the calculated local inflows. 1993: Three measurements were taken at 1,040 cfs, 1,483 cfs, and 2,312 cfs in 1993. The 1991 and 1992 rating curves were similar however, the 1993 rating curve shows a +0.18 foot shift. Mr. Piland attributed the change to a raise in the rock ripple control caused by above average snowmelt runoff in 1993 which likely deposited sediments at the controL Had the rating curve not been modified in 1993 the result would have been an over estimate of the flows by about 200 cfs. Again we caution the reader that flows were experienced in 1993 that exceeded 2,312 cfs and, therefore, that part-Of the rating curve remains unconfirmed. 12.21;. Five flow measurements were taken in 1994 ranging from 691 cfs to 2,413 cfs to develop the discharge rating curve. The discharge measurements made in 1994 support the rating curve developed in 1993 with a slight shift at the higher measured flows (> 2,000 cfs). This indicates that sediments believed deposited in 1993 at the control section were not flushed out in 1994. Measured flows during July through December ranged from 500 cfs to 2,950 cfs. Over the past four years one significant and several small shifts in the rating curve have been observed. This implies that stream flow measurements will need to be made each year to verify the rating curve, which is consistent with U.S.G.S. practices. If operation of the 27.5 Road Gage is to be continued for evaluation of local inflows to the critical reach then a minimum of at least one stream flow measurement per year is recommended. If a shift is suspected additional flow measurements should be made to define the new stage discharge relationship.