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Scientific Investigations Report 2012–5017


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Prepared in cooperation with the Molalla River Improvement District


Geomorphic Setting, Aquatic Habitat, and Water-Quality Conditions of the Molalla River, Oregon, 2009–10


By Kurt D. Carpenter, Christiana R. Czuba, Christopher S. Magirl, Mathieu D. Marineau, Steve Sobieszczyk, Jonathan A. Czuba, and Mackenzie K. Keith

Figures

Figure 1. Location and extent of the Molalla River study reach within the Molalla-Pudding River basin, Oregon.

Figure 2. Geomorphic flood plain, river centerline and river kilometer stationing, geomorphic flood-plain reaches, and geomorphic flood-plain centerline and flood-plain kilometer transect stationing, Molalla River, Oregon.

Figure 3. Locations of point-specific data collection sites along the Molalla River, Oregon.

Figure 4. Monthly mean precipitation and discharge of the Molalla River measured at the U.S. Geological Survey streamflow-gaging station Molalla River near Canby, Oregon.

Figure 5. Enhanced annual peak streamflow for the Molalla River near Canby, Oregon, 1909–2009.

Figure 6. Geomorphic flood-plain width along the Molalla River, Oregon.

Figure 7. Typical channel characteristics for each geomorphic reach in the lower Molalla River, Oregon.

Figure 8. Height above water surface of the Molalla River centered on each geomorphic reach.

Figure 9. Light Detection and Ranging (LiDAR)-derived longitudinal water-surface elevation profile of the Molalla River, Oregon, with elevation plotted in normal coordinates and semi-log coordinates.

Figure 10. Water depth data from the Molalla River, Oregon, as measured in July 2010 by a fathometer mounted to boat floating down the river thalweg.

Figure 11. Deviation of water-surface elevation profile from second-order polynomial trendline, and measured channel-bed and bedrock within the channel, Molalla River, Oregon.

Figure 12. Distribution of particle-size data collected using Wolman (1954) pebble counts on nine freshly deposited bars along the river corridor of the Molalla River, Oregon.

Figure 13. Comparison of measured geometry of five river cross sections surveyed on the Molalla River, Oregon.

Figure 14. Trends in stage of water-surface elevation at the U.S. Geological Survey streamflow-gaging station 14200000, Molalla River near Canby, Oregon.

Figure 15. Historical changes in channel sinuosity, averaged over geomorphic flood-plain reaches, for the Molalla River, Oregon, 1994–2009.

Figure 16. Historical changes in active-channel width, averaged over each 1-FPkm subreach segment, for the Molalla River, Oregon, 1994–2009.

Figure 17. Average annual channel-migration rates, averaged over each 1-FPkm subreach segment, for three time periods between aerial imagery, Molalla River, Oregon, 1994–2009.

Figure 18. Percentage of channel banks confined by bedrock, revetment, or Missoula Flood deposits along the Molalla River, Oregon, in 2010.

Figure 19. Historical changes in specific vegetated bar area averaged over each 1-FPkm subreach segment, separated by bar type and vegetation density, along the Molalla River, Oregon, 1994–2009.

Figure 20. Paneled mosaics of imagery of the river corridor in geomorphic reach 3 (GR3) for all available sets of aerial imagery. (Panel K shows the height-of-water-surface map along GR3 with Goods Bridge and the railroad bridge labeled and the river-stationing coordinates.)

Figure 21. Aerial imagery of the Molalla River in geomorphic reach 2 (GR2) near Canby, Oregon, in 1936 and 2009, showing the relative stability of channel form and location during most of the 20th century.

Figure 22. Aerial imagery of the Molalla River in geomorphic reach 1 (GR1) from near the confluence of the Willamette River in 1936 and 2009, showing a wide and active flood plain between the Pudding River and the Molalla River, Oregon.

Figure 23. Aerial imagery of the Molalla River, Oregon, in geomorphic reach 4 (GR4) just upstream of Highway 213 bridge (FPkm 19.5) to about FPkm 23 in 1948 and 2009.

Figure 24. Afternoon water temperature and specific conductance values for August–September 2000, August–September 2010, and longitudinal streamflow for various periods in the Molalla River, Oregon.

Figure 25. Water temperatures in the Molalla River, Oregon, August 2001.

Figure 26. Concentrations of dissolved oxygen and pH levels in the Molalla River, Oregon in August 2000, September 2000, August 2010, and September 2010.

Figure 27. Long-term trend in pH values in the lower Molalla River, 1965–2010.

Figure 28. Longitudinal nutrient concentrations in the main-stem Molalla River, Oregon, August and September 2010 and June 2000.

Figure 29. Summertime dissolved inorganic nitrogen and phosphorus concentrations in the Molalla River, Oregon, 1990–2010.

Figure 30. Longitudinal pattern in periphyton biomass (chlorophyll-a) in the main-stem Molalla River, Oregon, July and August 2010.

Figure 31. Longitudinal pattern in diatom indicators of water-quality conditions in the Molalla River, Oregon, in July and August 2010.

Figure 32. Multidimensional scaling ordination plot of algal samples from the Molalla River, Oregon, for the combined July and August 2010 samples.

First posted February 29, 2012

For additional information contact:
Director, Oregon Water Science Center
U.S. Geological Survey
2130 SW 5th Avenue
Portland, Oregon 97201
http://or.water.usgs.gov

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