Skagit River Hydrology Skagit River Hydrology Performed by Bill Cronin and Loren Jangaard Jangaard, USACE , USACE Performed by Bill Cronin and Loren Technically Reviewed by Ken Brettmann Brettmann, USACE , USACE Technically Reviewed by Ken Presented and Backchecked Backchecked by Ted Perkins by Ted Perkins Presented and
Skagit River Hydrology Skagit River Hydrology • Definition and Definition and • Objective Objective • Weather Patterns Weather Patterns • • Streamflow Streamflow • Analysis Analysis • Limits of Flood Limits of Flood • Control Control • Questions Questions •
Skagit River Hydrology Skagit River Hydrology Definition and Objective Definition and Objective Cards Chance of Recurrence Flood Event Cards Chance of Recurrence Flood Event Occurrence Occurrence 3 Clubs 1 in 52 1.9% 52- -year year 3 Clubs 1 in 52 1.9% 52 3 or 4 Clubs 1 in 26 1 in 26 3.8% 26- -year year 3 or 4 Clubs 3.8% 26 Flood Event Recurrence Chance of Flood Event Recurrence Chance of Occurrence Occurrence 10- -year year 10% 1 in 10 10 10% 1 in 10 100- -year year 1% 1 in 100 100 1% 1 in 100 500- -year year 0.2% 1 in 500 500 0.2% 1 in 500 How many cards are in the Hydrology deck?
Weather Patterns Weather Patterns •There are a lot of cards in the deck so need a long period of record
Hydrologic Record Hydrologic Record • Long Period of Long Period of • Record Record • Consistent human Consistent human • influence record influence record • Consistent natural Consistent natural • influence record influence record • Location Location •
Frequency Analyses Frequency Analyses Frequency EXCEEDANCE FREQUENCY IN PERCENT 99.0 98.0 95.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 5.0 2.0 1.0 0.5 0.2 0.1 • Rank Flood Rank Flood • 1,000,000 9 8 7 6 F 5 4 Events Events 3 l 2 DISCHARGE (cfs) 100,000 • Plot Data Plot Data 9 • o 8 7 6 5 4 w 3 • Peak, 1 Peak, 1- -day, day, • 2 10,000 3- -day, 7 day, 7- -day day 3 SKAGIT RIVER NEAR CONCRETE HEC-FFA COMPUTED CURVE USGS #12194000 EXPECTED PROBABILITY ADJUSTMENT UNREGULATED PEAK FLOWS 5% CONFIDENCE LIMITS DERIVED FROM PEAK VERSUS 1DAY REGRESSION 95% CONFIDENCE LIMITS CORPS OF ENGINEERS, SEATTLE DISTRICT MEDIAN PLOTTING POSITIONS 28 APR 1998 LOG TRANSFORM BASIN AREA= 2737 SQ MI SYSTEMATIC STATISTICS NUMBER OF EVENTS WATER YEARS OF RECORD HISTORIC EVENTS= 1898, 1909, 1917, 1921 MEAN= 4.9744 HISTORIC EVENTS= 4 ST. DEV.= 0.1744 HIGH OUTLIERS= 0 RECORDED EVENTS= 1925, 1944-1991, 1994-1996 COMPUTED SKEW= 0.6973 LOW OUTLIERS= 0 REGIONAL SKEW= 0.0000 ZERO OR MISSING= 0 CONSTRUCTED BY: APPROVED BY: ADOPTED SKEW= 0.5000 SYSTEMATIC EVENTS= 52 HISTORIC RECORD= 99 YRS ____________________________________ C. FITZGERALD, E.I.T.
Gage Assessment Gage Assessment Data Type Data Type Mount Vernon Mount Vernon Sedro Sedro- -Woolley Woolley Concrete Concrete Peak 1940- -present present 1896- -7, 1906, 7, 1906, 1897, 1909, Peak 1940 1896 1897, 1909, 1908- -22, 1975 22, 1975- -9 9 1917, 1921, 1908 1917, 1921, 1924- -present present 1924 Daily 1940- -present present 1908- -23, 1975 23, 1975- -80 80 1924- -present present Daily 1940 1908 1924 Years 58 22, 16 78, 74 Years 58 22, 16 78, 74 Problems Changed Slightly Changed Dam Influence Problems Changed Slightly Changed Dam Influence Watershed, Dam Watershed, Dam Watershed, Dam Watershed, Dam Influence, Influence, Influence, Influence, Attenuation Attenuation Attenuation Attenuation •Concrete Gage Has the Longest Consistent Record •All Gages are Used to Verify Results
The Impact of Volume on Peaks The Impact of Volume on Peaks CONW,MTVER 140000 Legend SKAGIT MTVER Skagit SKAGIT CONW 120000 Skagit River at Missing Data River at Concrete 100000 Mount F Vernon FLOW (CFS) 80000 l 60000 o w December 1975 Event 40000 20000 Time 0 02 03 04 05 06 07 08 Dec75 Time •The Volume of Water at Concrete is Accounted for Downstream •Longer Duration Flood Creates Higher Peak Downstream
The Impact of Volume on Peaks The Impact of Volume on Peaks CONW,MVEW 160000 Legend SKAGIT MVEW Skagit SKAGIT CONW Skagit River at 140000 SKAGIT MVEW River at SKAGIT CONW Concrete Missing Data Mount FLOW REG (CFS) FLOW (CFS) 120000 F Vernon l 100000 o 80000 w November 1995 Event 60000 Time 40000 28 29 30 01 02 03 04 Nov95 Dec95 Time •The Volume of Water at Concrete is Accounted for Downstream •Shorter Duration Flood Results in Lower Peak Downstream
Influence of Dams Influence of Dams Year Dam Note Year Dam Note 1924 Low Low First Built 1924 First Built Gorge Gorge 1954 Ross Ross Flood 1954 Flood Storage Storage 1956 Upper Upper Flood 1956 Flood Baker Storage Baker Storage 1977 Upper Upper Added Flood 1977 Added Flood Baker Storage Baker Storage
With Dams Frequency Curve With Dams Frequency Curve EXCEEDANCE FREQUENCY IN PERCENT • Concrete Dam Concrete Dam • 99.0 98.0 95.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 5.0 2.0 0.2 1.0 1,000,000 900000.00 800000.00 700000.00 Influenced Data Influenced Data 600000.00 500000.00 400000.00 (1956- -97) 97) (1956 300000.00 200000.00 • Control flow when Control flow when • DISCHARGE (cfs) 100,000 90000.00 expected to exceed expected to exceed 80000.00 70000.00 60000.00 50000.00 90,000 cfs cfs at Concrete at Concrete 90,000 40000.00 30000.00 • From 1956 From 1956- -77, only 2 77, only 2 20000.00 • events are regulated events are regulated 10,000 REGULATED OBSERVED MEDIAN PLOTTING POSITIONS SKAGIT RIVER NEAR CONCRETE POLYNOMIAL BEST FIT LINE OBSERVED DATA USGS #12194000 REGULATED PEAK FLOW FREQUENCY CURVE (11/20/62- -114,000 114,000 cfs cfs, , (11/20/62 CORPS OF ENGINEERS, SEATTLE DISTRICT 28 APR 1998 LOG TRANSFORM BASIN AREA= 2737 SQ MI SYSTEMATIC STATISTICS NUMBER OF EVENTS OBSERVED WATER YEARS OF RECORD 12/4/75 – – 122,000 122,000 cfs cfs) ) 12/4/75 1956-1997 MEAN= HISTORIC EVENTS= ST. DEV.= HIGH OUTLIERS= COMPUTED SKEW= LOW OUTLIERS= REGIONAL SKEW= ZERO OR MISSING= CONSTRUCTED BY: APPROVED BY: ADOPTED SKEW= SYSTEMATIC EVENTS= WE CRONIN, P.E. ____________________________________ 40 year Record of Dam Controlled Peak Flows
Determine Relationship between Pre- - Determine Relationship between Pre Dam and Post- -Dam Flows Dam Flows Dam and Post • Determine Dam • Determine Dam Inflows Inflows • Determine Local • Determine Local Flows Between Flows Between Dams and Concrete Dams and Concrete • Route to get Without • Route to get Without Dam Flow at Dam Flow at Concrete Concrete • Perform Frequency • Perform Frequency Analysis Analysis A Longer Period of Record is Developed for the Without Dam Condition
Without Dam Flows at Concrete Without Dam Flows at Concrete EXCEEDANCE FREQUENCY IN PERCENT 99.0 98.0 95.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 5.0 2.0 1.0 0.5 0.2 0.1 • Determine Upper Without • Determine Upper Without 1,000,000 9 8 7 Dam Frequency Events Dam Frequency Events 6 5 4 • Correlate to Dam Inflows 3 • Correlate to Dam Inflows 2 DISCHARGE (cfs) • Set Up Reservoir Model to • Set Up Reservoir Model to 100,000 9 Current Conditions 8 Current Conditions 7 6 5 4 • Route these inflows • Route these inflows 3 through dams, add in local through dams, add in local 2 to determine peaks at to determine peaks at 10,000 SKAGIT RIVER NEAR CONCRETE HEC-FFA COMPUTED CURVE USGS #12194000 Concrete Concrete EXPECTED PROBABILITY ADJUSTMENT UNREGULATED PEAK FLOWS 5% CONFIDENCE LIMITS DERIVED FROM PEAK VERSUS 1DAY REGRESSION 95% CONFIDENCE LIMITS CORPS OF ENGINEERS, SEATTLE DISTRICT MEDIAN PLOTTING POSITIONS 28 APR 1998 LOG TRANSFORM BASIN AREA= 2737 SQ MI SYSTEMATIC STATISTICS NUMBER OF EVENTS WATER YEARS OF RECORD HISTORIC EVENTS= 1898, 1909, 1917, 1921 MEAN= 4.9744 HISTORIC EVENTS= 4 ST. DEV.= 0.1744 HIGH OUTLIERS= 0 RECORDED EVENTS= 1925, 1944-1991, 1994-1996 COMPUTED SKEW= 0.6973 LOW OUTLIERS= 0 REGIONAL SKEW= 0.0000 ZERO OR MISSING= 0 CONSTRUCTED BY: APPROVED BY: ADOPTED SKEW= 0.5000 SYSTEMATIC EVENTS= 52 HISTORIC RECORD= 99 YRS ____________________________________ C. FITZGERALD, E.I.T. We can route large hypothetical floods through dams
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