Scientific Investigations Report 2008–5059
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5059
Table 2. Effective porosity and seasonal water-table fluctuations by hydrogeologic unit in the Portland, Oregon area.
[–, unknown. No wells had a zone of fluctuation within the sand and gravel aquifer]
| Properties | Hydrogeologic unit | ||||||
|---|---|---|---|---|---|---|---|
| Unconsolidated sedimentary aquifer |
Troutdale gravel aquifer |
Undifferentiated fine-grained unit |
Troutdale sandstone aquifer |
Sand and gravel aquifer |
Older rocks |
All hydrogeologic units |
|
| Mean effective porosity (dimensionless) | 0.31 | 0.28 | 0.21 | 0.29 | 0.26 | 0.15 | 10.23 |
| Predicted seasonal water-table fluctuation as calculated using mean effective porosity and mean average annual recharge (feet) | 5.9 | 6.5 | 8.7 | 6.3 | 7.1 | 12.2 | 8.0 |
| Mean of measured seasonal water-table fluctuations (feet)2 | 5.9 | 8.0 | 7.3 | 6.9 | – | 11.0 | 6.8 |
| Number of wells used for analysis with zone of fluctuation within the hydrogeologic unit | 63 | 39 | 9 | 14 | 0 | 2 | 127 |
1 Weighted mean by areal extent in the Portland Basin (see Hinkle and Snyder, 1997, p. 39-47).
2 Values of measured seasonal water-level fluctuation presented are the trimmed values that include the central 90 percent of the water-level measurements for the period of record of each well.
U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2008/5059
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