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Scientific Investigations Report 2012–5017


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


Table 14. Physical characteristics for five sites sampled for water quality and algae in the Molalla River, Oregon.


[Abbreviations: D10, size of sediment for which 10 percent of the sample is finer; D50, median particle size; D90, size of sediment for which 90 percent of the sample is finer; FPkm, flood plain kilometer; km, kilometer; km2, square kilometer; LiDAR, light detection and ranging; m, meter; mm, millimeter; m/m, meter per meter; m/s, meter per second; m/yr, meter per year; m2/m, square meter per meter; m3/s, cubic meter per second; n/a, no data available]

Variable Molalla River sampling site
Upstream of
Glen Avon
Bridge
Upstream of
Highway 211
Bridge
Upstream of
Highway 213
Bridge
Upstream
of Goods
Bridge
Downstream
of Knights
Bridge
Instream/site characteristics
  Dominant land cover
Forested Forested/
rural/
agricultural
Rural/
agricultural/
forested
Rural/
agricultural
Rural/
agricultural/
urban
Elevation (m) 163 97 72 33 23
LiDAR river stationing (km) 44.20 31.07 23.40 10.50 4.75
D10 particle size (mm) 32 38 29 25 14
D50 particle size (mm) 108 71 95 71 41
D90 particle size (mm) 316 157 156 139 77
Sand, percent 1.25 0.0 0 2 5.5
Drainage area (km2) 344 531 546 842 893
Low flow discharge (10 percent exceedance) (m3/s) 0.90 1.39 1.43 2.21 2.34
Median discharge (50 percent exceedance) (m3/s) 7.72 11.9 12.3 18.9 20.0
Bankfull discharge (2-year flood) (m3/s) 157 243 250 385 408
Water velocity at low flow, 90 percent exceedance (m/s) 0.39 0.52 0.45 0.47 0.54
Water velocity at median discharge, 50 percent exceedance (m/s) 0.83 1.06 1.00 0.91 1.04
Water velocity at bankfull discharge (2-year flood) (m/s) 2.41 2.56 2.27 2.53 2.79
Averaged residual pool depth (m) n/a 0.4 1.7 0.7 0.4
Average water surface slope for 1 kilometer reach (m/m) 0.005 0.004 0.003 0.002 0.001
Presence of local streambed bedrock Yes Yes Yes No Yes
Presence of local gravel bars No Yes Yes Yes No
Flood-plain and channel characteristics
Geomorphic flood plain FPkm segment (km) 36 25 20 10 4
FPkm segment average flood plain width (km) 0.21 1.13 0.90 0.83 2.66
Local flood plain width, (km) 0.10 0.98 0.98 0.70 2.25
1994 active channel width (m) 29.5 38.8 44.7 44.1 30.3
2000 active channel width (m) 27.1 47.1 60.8 52.3 34.5
2005 active channel width (m) 27.4 35.1 39.8 47.5 35.0
2009 active channel width (m) 31.2 33.9 45.9 56.7 35.7
Averaged active channel width (m) 28.8 38.7 47.8 50.1 33.9
1994–2000 annual migration rate (m/yr) 1.02 2.27 3.43 1.62 1.11
2000–2005 annual migration rate (m/yr) 1.00 0.55 0.88 1.15 0.48
2005–2009 annual migration rate (m/yr) 1.36 1.58 1.92 3.70 2.05
Time-weighted annual migration rate (m/yr) 1.10 1.52 2.19 2.00 1.14
Gemorphic reach average percent confined banks 44.9 21.1 21.1 15.1 24.2
FPkm segment average percent confined banks 23.4 48.1 26.0 41.2 51.3
Local bank confinement (number: 0,1,2 banks confined) 0 2 0 2 2
1994 channel sinuosity 1.10 1.35 1.35 1.29 1.05
2000 channel sinuosity 1.12 1.39 1.39 1.45 1.08
2005 channel sinuosity 1.10 1.39 1.39 1.44 1.08
2009 channel sinuosity 1.10 1.40 1.40 1.29 1.09
Average sinuosity 1.10 1.38 1.38 1.37 1.07
2009 specific bar area in FPkm segment (m2/m) 6.68 24.73 56.60 19.47 8.31
2009 percentage of bare vegetation on bars 55.15 83.36 37.96 30.85 74.43
2009 percentage of moderate vegetation on bars 0 0 56.66 69.15 14.47
2009 percentage of dense vegetation on bars 44.85 16.64 5.38 0 11.10

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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