1. The flow or movement of water
Hydrology
The flow or movement of water

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

3. Surface Runoff
Surface hydrology focuses primarily on streams and their channels

4. 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

5. 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
Water Year = Oct - Sept

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

7. 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

8. Multi-year Hydrograph
Jan-02
Flood Stage

9. 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?

10. 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

11. 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

12. 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
= = 4 2
For Gales Creek, 1996 was a “4-year flood”

13. 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

14. 1996
1862 is the Historic Peak for this site

16. 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
= = 3.5 34
For the Willamette in Albany, 1996 was a “3-4 year flood”

18. 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
= = 30 1
For the Willamette in Portland, 1996 was a “30-year flood”

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

20. 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

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

23. 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

24. Width to Depth Ratio
Width / Depth at Bankfull

25. 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.

26. 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

28. 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

29. 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

31. Rosgen Stream Classification