USGS Scientific Investigations Report 2011–5191  - Seepage Investigations of the Clackamas River, Oregon 

Table 2. Streamflow gains and losses in the lower Clackamas River, Oregon, 1963–2006. 

[Site number: See table 1. Locations of reaches and sites are shown in figure 2. Values greater than streamflow uncertainty are depicted in bold. Downstream site streamflows are adjusted for tributary or withdrawal. Noted gains and losses are from upstream to downstream sites. Abbreviations: ft³/s, cubic foot per second; +, gain from upstream site; - , loss from upstream site; (a), value from streamflow monitoring site; WY, water year (the year extending from October 1 of the previous year to September 30 of the year indicated] 

Date	Upstream site		Downstream site		Streamflow uncertainty (percent)	Gain or loss		Remarks
Date	Site number	Streamflow (ft³/s)	Site number	Streamflow (ft³/s)	Streamflow uncertainty (percent)	(ft³/s)	(percent)	Remarks
Previous studies
08-26-1987	5	650 (a)	25	754	10	+104	+16	Estimated tributary inflow (site numbers 11, 14, 20, and 23) equal to September 2006 measurements.
05-14-1992	5	1,350 (a)	13	1,200	10	-150	-11
09-01-1998	5	1,000 (a)	13	1,060	10	+60	+6	Estimated tributary inflow (site number 11) equal to September 2006 measurement.
09-01-1998	13	1,080	21	1,280	8	+200	+19	Estimated tributary inflow (site numbers 14, 20) equal to September 2006 measurements.
Long-term streamflow data
WY 1963–1983 average of daily means (August and September)	5	943 (a)	25	992 (a)	10	+49	+5	Estimated tributary inflow (site numbers 11, 14, 20, and 23) equal to September 2006 measurements.
WY 2001–2006 average of daily means (August and September)	5	848 (a)	32	853 (a)	10	+5	+1	Estimated tributary inflow (site numbers 11, 14, 20, and 23) equal to September 2006 measurements. Includes reported withdrawals (site numbers 27, 29, and 31).
Summary of 2006 seepage study
09-06-2006	6	756	10	751	8	-5	-1	Reach A
09-06-2006	10	751	13	693	8	-58	-8	Reach B
09-06-2006	13	714	17	726	5	+12	+2	Reach C
09-06-2006	17	731	22	830	8	+99	+14	Reach D
09-06-2006	22	845	25	741	11	-104	-12	Reach E
09-06-2006	25	742	28	782	11	+40	+5	Reach F
09-07-2006	5	779	25	730	10	-49	-6	Reach A through E
09-07-2006	25	772	28	817	11	+45	+6	Reach F