The flow or movement of water Hydrology The flow or movement of water

Hydrologic cycle Student Watershed Research Project (SWRP) PSU - Environmental Sciences and Resources

Surface Runoff Surface hydrology focuses primarily on streams and their channels

Measuring Flow Discharge or gage height commonly used for surface water flows Discharge or flow are measured in ft3/sec or m3/sec Width x depth x velocity = flow Width to depth ratio

Hydrographs Graph of a stream’s discharge over time “Real-time” and historical data may be available through Water Resources Dept, your local watermaster or USGS http://waterdata.usgs.gov/nwis Water Year = Oct - Sept

Annual Hydrograph 10/7/01 is when flow begins to increase above 10 cfs

Peak Flows Watermaster has determined 1,873 cfs to be “flood stage” for this site Gales Creek exceeded this level 4 times in water year 2001 Highest discharge for year = 4,622 csf on 1/8/02

Multi-year Hydrograph Jan-02 Flood Stage

Flood Frequency Gales Creek appears to reach “flood stage” at least once per year (except 2001) 1999 appears to have highest discharge for the 8 years we have data for – even higher than 1996 What makes a 100-year flood?

Flood Frequency Find maximum annual discharges Can query “Peak Streamflow” on USGS site Rank peak discharges from largest to smallest Calculate recurrence interval (RI) RI = # years + 1 flood rank

Gales Creek Peak Streamflow Year Flow (cfs) 1995 2490 1996 4780 1997 2660 1998 2770 1999 6170 2000 2500 2001 4622 Rank Year Flow (cfs) 1 1999 6170 2 1996 4780 3 2001 4622 4 1998 2770 5 1997 2660 6 2000 2500 7 1995 2490

Recurrence Interval Recurrence Interval = # years + 1 flood rank Discharge (cfs) 1999 6170 1996 4780 2001 4622 1998 2770 1997 2660 2000 2500 1995 2490 Recurrence Interval = # years + 1 flood rank = 7 + 1 = 4 2 For Gales Creek, 1996 was a “4-year flood”

100-Year Flood Requires 99 years of data Only the largest flood during that 100 year period would be a “100-year flood” Very few sites with 100 years of data The Flood of 1996 was far from a 100-year event

1996 1862 is the Historic Peak for this site

Flood Recurrence at Albany Rank Year Discharge (cfs) 1 1862 340,000 2 1890 291,000 3 1881 266,000 34 1996 125,000 35 1922 122,000 36 1909 119,000 117 1977 18,000 = 117 + 1 = 3.5 34 For the Willamette in Albany, 1996 was a “3-4 year flood”

Flood Recurrence at Portland Rank Year Discharge (cfs) 1 1996 420,000 2 1997 293,000 3 1974 283,000 26 1992 105,000 27 1991 102,000 28 1977 58,100 29 2001 53,000 = 29 + 1 = 30 1 For the Willamette in Portland, 1996 was a “30-year flood”

Stream Channel The energy from gradient can alter the Sinuosity Entrenchment Width to Depth Ratio of a stream channel below bankfull

Determining “Bankfull” channel Top of point bar Change in vegetation Topographic break in slope Staining or change in substrate material or size Change in nature or amount of debris deposits

Entrenchment Vertical containment Estimated as: Width of stream at 2x bankfull depth Width at bankfull Width @ 2x Bankfull Depth (Floodprone Width) Width @ Bankfull

Entrenchment Entrenchment Entrenched <1.4 Moderately Entrenched 1.4 – 2.2 Slightly Entrenched >2.2 Entrenchment of 1.0 means the floodprone width = bankfull width

Width to Depth Ratio Width / Depth at Bankfull

Width to Depth Width/Depth Ratio Low <12 Moderate 12 – 40 High >40 As the width to depth ratio increases, the stream gets wider and shallower.

Sinuosity Is stream straight or does it meander? How much longer would channel be if it were stretched into a straight line? Estimated as: Channel length Straight length

Sinuosity Sinuosity Low <1.2 Moderate 1.2 – 1.5 High >1.5 Sinuosity of 1.0 means the stream channel has the same gradient as the valley

Gradient Channel slope (Rise over Run) Can be difficult to measure, estimate by characteristics: Gradient Characteristics 0-2% Calm water surface; almost no sound 2-4% Rough surface; must raise voice slightly to be heard >4% Turbulent flow; must shout to be heard

Rosgen Stream Classification