lecture 19: down-stream floods and the “100-year” floodlecture 19: down-stream floods and the...

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Lecture 19: Down-Stream Floods and the “100-Year” Flood Key Questions 1. What is a downstream flood? 2. What were the setup conditions that caused the Nov, 1990 Nooksack flood? 3. What is a 100-year flood? 4. How are 100-year flood discharge magnitudes determined? 5. What is a 100-year flood inundation map? 6. Mitigation techniques Niigata Japan, 1964 liquefaction Chehalis Dec 2007 Flood (Seattle Times)

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Page 1: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Lecture 19: Down-Stream Floods and the “100-Year” Flood

Key Questions1. What is a downstream flood?

2. What were the setup conditions that caused the Nov, 1990 Nooksack flood?

3. What is a 100-year flood?

4. How are 100-year flood discharge magnitudes determined?

5. What is a 100-year flood inundation map?

6. Mitigation techniques

Niigata Japan, 1964 liquefaction

Chehalis Dec 2007 Flood (Seattle Times)

Page 2: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Down Stream Floods occur in areas of low relief (floodplains)

Page 3: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

http://courses.washington.edu/uwtoce06/puget%20sound%20watershed.jpg

Page 4: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

http://wa.water.usgs.gov/data/realtime/adr/interactive/maps/NooksackSC_basin.pdf

Nooksack River Basin

About 2000 square kilometers or 780 square miles

Page 5: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

PNW FLOODS are caused by heavy rains and/or rapid snow melt—their severity is controlled by the WATERSHED characteristics.

Page 7: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

November, 1990 FloodJanuary, 2009 Flood

Page 8: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Conditions for Setup for the Nooksack River, November 10, 1990 Flood

1. Heavy Rain5 inches of rain in Bellingham in 3 days

14 inches fell in the mountains

http://seattlepi.nwsource.com/photos/popup.asp?SubID=2012&page=2&GTitle=Storm%20of%20December%2C%202006&css=gtitle%2Ecss&pubdate=12/19/2006

Page 9: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

http://virga.sfsu.edu/pub/jetstream/jetstream_pac/big/0712/07120318_jetstream_pac_anal.gif

Pineapple Express: December 3, 2007

Page 10: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

http://virga.sfsu.edu/pub/jetstream/jetstream_pac/big/0901/09010900_jetstream_pac_anal.gif

Pineapple Express: January 8, 2009

Page 11: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

clouds cool when they

expand

water vapor condenses when it cools which produces rain

Orographic Effect

70% of the Nooksack basin is steep terrain.

Page 12: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

soils near saturation produce more runoff

Q

Time

Hydrograph

Conditions for Setup for the Nooksack River, November 10, 1990 Flood

2. In November, soils are nearly saturated

runoff

Page 13: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Conditions for Setup for the Nooksack River, November 10, 1990 Flood

3. Rain on Snow

John Scurlock

Page 14: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

3. Rain on SnowNovember snow packs are relatively warm. Warm rains release heat into the snowapck causing some snow to melt.

Snowmelt produced an additional 2 inches of runoff!

Q

Time

Hydrograph

runoff

Page 15: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

SNOTEL stations are used to monitor snow depth

SNOTEL = SNOwpack TELemetry

Page 17: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Q

Time

Hydrograph

Q

Time

Hydrograph

snow packno snow pack so rain falls on exposed bedrock and thin, wet soils

more volume but less peaked

Q Q

Page 18: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Conditions for Setup for the Nooksack River, November 10, 1990 Flood

4. High TideHigh tide caused the river mouth to be higher (pushes water back on the floodplain).

5. Storm SurgeStorm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm.

http://en.wikipedia.org/wiki/Image:Surge-en.svg

Page 19: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Nooksack River, November, 1990 Flood

Page 20: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Flood risk questions:

1. When are floods most likely to occur?

Page 21: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Collect the historical peak flows for a river (e.g., Nooksack at Ferndale).

10/26/1945 41600

11/27/1949 27500

2/10/1951 55000

1/31/1952 18300

2/1/1953 19300

10/31/1953 18500

11/19/1954 20700

11/4/1955 35000

12/10/1956 23000

1/17/1958 18300

4/30/1959 30200

11/23/1959 22000

1/16/1961 30800

1/8/1962 18800

11/20/1962 26000

11/27/1963 23300

1/31/1965 20000

12/4/1965 17500

12/14/1966 21400

12/26/1967 23900

1/5/1969 28100

11/5/1969 17300

1/31/1971 38100

3/6/1972 24800

12/26/1972 24800

1/17/1974 21800

12/21/1974 20800

12/3/1975 46700

1/18/1977 20600

12/3/1977 23900

11/8/1978 18800

12/15/1979 36400

12/27/1980 29700

2/15/1982 27200

1/11/1983 34200

1/5/1984 41500

4/27/1985 16300

2/25/1986 29900

11/24/1986 36000

4/6/1988 17700

10/16/1988 21000

11/11/1989 47800

11/10/1990 57000

1/24/1992 18100

1/25/1993 19000

3/2/1994 18500

12/20/1994 21700

11/30/1995 47200

3/20/1997 38100

10/30/1997 17600

12/14/1998 24600

12/16/1999 22200

10/21/2000 14300

2/23/2002 30300

1/26/2003 20100

10/21/2003 39900

11/25/2004 42300

1/10/2006 19500

11/7/2006 38100

12/4/2007 21100

Year cfs Year cfs Year cfs Year cfs

Page 22: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Flood risk questions:

1. When are flood most likely to occur?

Monthly Occurrence of Peak Flows at Ferndale

Page 23: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Flood risk questions:

1. When are flood most likely to occur?

2. How often do large magnitude floods occur?

Page 24: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

A “100-year flood” is a large magnitude flood that has a 1% chance occurring in any given year

Chehalis Flood, Dec 2007 (Seattle Tiimes photo)

Page 25: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

A 100-year flood inundation map is one of the primary mitigation tools that is used to lower the risk of being impacted by a downstream flood

Page 26: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

100-year flood risks are determined using historical data and statistical techniques

Page 27: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

1. Collect the historical peak flows for a river (e.g., Nooksack at Ferndale).

10/26/1945 41600

11/27/1949 27500

2/10/1951 55000

1/31/1952 18300

2/1/1953 19300

10/31/1953 18500

11/19/1954 20700

11/4/1955 35000

12/10/1956 23000

1/17/1958 18300

4/30/1959 30200

11/23/1959 22000

1/16/1961 30800

1/8/1962 18800

11/20/1962 26000

11/27/1963 23300

1/31/1965 20000

12/4/1965 17500

12/14/1966 21400

12/26/1967 23900

1/5/1969 28100

11/5/1969 17300

1/31/1971 38100

3/6/1972 24800

12/26/1972 24800

1/17/1974 21800

12/21/1974 20800

12/3/1975 46700

1/18/1977 20600

12/3/1977 23900

11/8/1978 18800

12/15/1979 36400

12/27/1980 29700

2/15/1982 27200

1/11/1983 34200

1/5/1984 41500

4/27/1985 16300

2/25/1986 29900

11/24/1986 36000

4/6/1988 17700

10/16/1988 21000

11/11/1989 47800

11/10/1990 57000

1/24/1992 18100

1/25/1993 19000

3/2/1994 18500

12/20/1994 21700

11/30/1995 47200

3/20/1997 38100

10/30/1997 17600

12/14/1998 24600

12/16/1999 22200

10/21/2000 14300

2/23/2002 30300

1/26/2003 20100

10/21/2003 39900

11/25/2004 42300

1/10/2006 19500

11/7/2006 38100

12/4/2007 21100

Year cfs Year cfs Year cfs Year cfs

Page 28: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

2. “Rank” the peak flow discharges from highest to lowest.

1 57000

2 55000

3 47800

4 47200

5 46700

6 42300

7 41600

8 41500

9 39900

10 38100

11 38100

12 38100

13 36400

. .

. .

. .57 17300

58 16300

59 14300

Rank cfs

Page 29: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

3. Estimate the exceedance probability “P” using the ranked values and the Weibull position formula.

P = m

n + 1m = rank

n = total number of values

in this case “n = 60”

Page 30: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

P = m

n + 1m = rank

n = total number of values

Example: for m = 12

P = 12

59 + 1 = 0.20

The discharge for “m = 12” is 38,100 cfs. This means that in any given year there is a 0.20 probability or a 20% chance of “peak flow” occurring that will equal or exceed a Q of 38,100 cfs.

Page 31: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

4. The exceedance probability can be used to estimate the return period of a certain peak flow.

Return Period = 1P

Example: for m = 12 P = 0.20

The means that one can expect flood with a peak flow of about 38,100 cfs every 5 years.

Return Period = 1

0.20= 5 years

where

Page 32: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Nooksack at Ferndale - Peak Flow

Date Water YearPeak Flow Q

(cfs) RANK #Peak Discharge

(cfs) Exceedence

ProbabilityReturn Period

(years)

10/26/1945 1946 41600 1 57000 0.02 59.00

11/27/1949 1950 27500 2 55000 0.03 29.50

2/10/1951 1951 55000 3 47800 0.05 19.67

1/31/1952 1952 18300 4 47200 0.07 14.75

2/1/1953 1953 19300 5 46700 0.08 11.80

10/31/1953 1954 18500 6 42300 0.10 9.83

11/19/1954 1955 20700 7 41600 0.12 8.43

11/4/1955 1956 35000 8 41500 0.14 7.38

12/10/1956 1957 23000 9 39900 0.15 6.56

1/17/1958 1958 18300 10 38100 0.17 5.90

4/30/1959 1959 30200 11 38100 0.19 5.36

11/23/1959 1960 22000 12 38100 0.20 4.92

1/16/1961 1961 30800 13 36400 0.22 4.54

1/8/1962 1962 18800 14 36000 0.24 4.21

11/20/1962 1963 26000 15 35000 0.25 3.93

11/27/1963 1964 23300 16 34200 0.27 3.69

1/31/1965 1965 20000 17 30800 0.29 3.47

12/4/1965 1966 17500 18 30300 0.31 3.28

12/14/1966 1967 21400 19 30200 0.32 3.11

12/26/1967 1968 23900 20 29900 0.34 2.95

1/5/1969 1969 28100 21 29700 0.36 2.81

Page 33: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

A 100-year flood is a flood that has a return period of 100 years

Return Period = 100 years

Page 34: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Estimate the Discharge of a “100-year flood”

1. Plot all the peak flows on the vertical axis (arithmetic scale) versus their respective return periods on the horizontal axis (log10 scale).

0

10000

20000

30000

40000

50000

60000

70000

80000

1 10 100

Return Period (years)

Peak

Dis

char

ge (c

fs)

Page 35: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Estimate the Discharge of a “100-year flood”

2. Add a linear trend line to the data and extrapolate out in time.

0

10000

20000

30000

40000

50000

60000

70000

80000

1 10 100

Return Period (years)

Peak

Dis

char

ge (c

fs)

Page 36: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Estimate the Discharge of a “100-year flood”

3. Extrapolate out in time (100 years) and estimate the discharge.

0

10000

20000

30000

40000

50000

60000

70000

80000

1 10 100

Return Period (years)

Peak

Dis

char

ge (c

fs)

Page 37: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

100-year Floodplain Map

Page 38: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Estimate the stage of a “100-year flood”

0

10000

20000

30000

40000

50000

60000

70000

10 12 14 16 18 20 22 24 26

Gauge Height (feet)

Dis

char

ge (c

fs)

Rating Curve

Page 39: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

22.76 feet

Page 41: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Structural Techniques

1. Levees are engineered embankments designed to contain the river

Page 42: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Structural Techniques

Levees are typically design to contain moderately sized floods

levee

Page 43: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Structural Techniques

2. Dams can store and slowly release water

storage capacity

monitored release

Δ

=

Page 45: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Land Purchases

Page 46: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Insurance

Page 47: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were

Mitigation: Emergency Response

Page 49: Lecture 19: Down-Stream Floods and the “100-Year” FloodLecture 19: Down-Stream Floods and the “100-Year” Flood . Key Questions. 1. What is a downstream flood? 2. What were