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

Table 3. Streamflow gains of the Clackamas River, Oregon, within three hydrogeologic areas of the Willamette River basin, 1963–83 and 2001–06. 

[Upstream and downstream monitoring site number: See table 1; locations of sites are shown in figures 1 and 2. Gain in streamflow: Based on data from August and September 1963–83 and 2001–06. Values in bold are significant (greater than the streamflow uncertainty). Abbreviations: (a), average; mi², square mile; ft³/s, cubic foot per second; (ft³/s)/mi², cubic foot second per square mile] 

Hydrogeologic area	Upstream and downstream monitoring site number	Intervening drainage area (mi²)	Gain in streamflow over intervening drainage area (ft³/s)	Normalized gain over intervening drainage area ([ft³/s]/mi²)
High Cascade	1, 2	70	223	3.2
Western Cascade (upper)	2, 3	355	446	1.2
Western Cascade (lower)	3, 5	192	160	0.8
Willamette Lowland	5, 25 (1963–83) 5, 32 (2001–06)	265 (a)	70	0.3