Hydraulic Modeling of the Missoula Ice Dam Failure. Christopher R. Goodell, P.E., D.WRE WEST Consultants, Salem, OR

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1 Hydraulic Modeling of the Missoula Ice Dam Failure Christopher R. Goodell, P.E., D.WRE WEST Consultants, Salem, OR 1

Introduction 10-40 thousand years ago during the

2 Introduction thousand years ago during the last ice age Image courtesy gis4geomorphology.com

3 Introduction These glaciers: Were up to 100 s of meters thick Would occasionally block freeflowing rivers. Image courtesy pbs.org

filled to a level that caused the ice dam to break.

4 Introduction Glacier blocked the natural outlet for the Clark Fork River With no alternative outlet, the glacial lake rose until it filled to a level that caused the ice dam to break. Glacial Lake Missoula Image courtesy sandpointonline.com, Illustration by Bruce Bjornstad.

5 Introduction Glacial Lake Missoula Stats About 1,970 ft deep at the ice dam (Same as Crater Lake) Surface Area = 2900 sq. miles, 7500 km 2 Volume = 500 miles 3, 2084 km 3, 1.7 Billion acre-ft. About half of Lake Michigan, or equivalent to Lake Erie and Lake Ontario combined. About 290 meters deep at Missoula, MT Image courtesy hugefloods.com Image courtesy sites.coloradocollege.edu

Solving the Mystery J Harlen Bretz Geologist from University of Chicago Wondered about the many odd and large scale geologic features of Eastern Washington-Scablands.

6 Solving the Mystery J Harlen Bretz Geologist from University of Chicago Wondered about the many odd and large scale geologic features of Eastern Washington-Scablands. In 1923, he proposed a Catastrophic Flood was responsible. HERETIC! Uniformitarianism was the theory du jour in the geologic community and there was no room for the backwards thinking of Catastrophists. Not until 1965 did the geologic community as a whole embrace Bretz s theories. In 1979, at the age of 96, Bretz was awarded the Penrose Medal. What did he see that drew his attention?

7 Solving the Mystery Dry Falls Image courtesy tau0.wordpress.com 3 miles wide (5 times wider than Niagara) 350 ft drop! (> 2 times higher than Niagara) > 10 times the volume of all the rivers in the world combined.

8 Solving the Mystery Giant Ripples West Bar Washington Google Earth 50 ft high with wavelengths of 500 ft hugefloods.com

9 Solving the Mystery Giant Ripples Markle Pass and Camas Prairie, MT Google Earth Camas Prairie, MT, hugefloods.com

10 Solving the Mystery Giant Ripples???

11 Solving the Mystery Columbia River Gorge

12 Solving the Mystery Rocky Butte

13 Solving the Mystery Lake Oswego

14 Solving the Mystery Ice Rafted Erratics BruceBjornstad.com HugeFloods.com BruceBjornstad.com

15 Solving the Mystery Erratics Yeager Rock, Mansfield, WA

16 Solving the Mystery Erratics Badger Coulee Vineyard

17 Solving the Mystery Erratics

18 Bellevue Erratic

19 Hydraulic Modeling of the Missoula Floods Dam Breach Modeling Important component in dam safety programs Has been applied to modern-day glacial lake outbursts (Himalayas) Jokulhlaups

20 Modeling Approach HEC-RAS One-Dimensional unsteady flow model. Has Dam Breach capability Has many built-in stabilizing techniques But can it handle this?

21 Modeling Approach Terrain Model 1 o DEM from USGS EROS site, scale 1:250k Vertical Resolution 30 meters, Horizontal Resolution ~ 130 meters Converted to an ESRI Grid

22 Modeling Approach Flow Path Approximation 1-D model Not as difficult as first thought! Aerial Photos and DEM s

23 Modeling Approach Initial Spacing about 5 km 2,346 Cross Sections 68 Reaches 34 Junctions 36 External Boundaries

24 Modeling Approach Inline and Lateral Structures

Modeling Approach Flow Data Constant Inflow Hydrographs (Sunny Day Event) Inflow Values approximated by USGS stream gage data (when available) Precise initial

25 Modeling Approach Flow Data Constant Inflow Hydrographs (Sunny Day Event) Inflow Values approximated by USGS stream gage data (when available) Precise initial conditions not necessary Flood wave 100 times greater than all streams combined. Downstream Boundary: Normal Depth. Applied upstream of the Mouth of the Columbia.

26 Model Development/Assumptions Defining the Breach Piping hr development Breach width??? Hubbard Glacier Jokulhlaup

27 Model Development/Assumptions Numerical Stability 2000 m Blind Interpolation Down to 500 m in some areas 30 second time step (Courant Condition)

28 Model Development/Assumptions Channel Modification Pilot Channels Channel Modification Tool

29 Model Development/Assumptions Hotstart Flow Distributions, Junctions & Lateral Structures Step-Down Scheme

30 Model Development/Assumptions Sediment Transport Undoubtedly a LOT of sediment movement occurred. Wind-blown silt thought to accumulate to depths of several hundred feet in the Eastern Washington Scablands prior to the Missoula Floods Where did the silt go? How did it affect the flooding? How does this affect the modeling effort?

31 Model Development/Assumptions Advance/Retreat of Glaciers Flood Morphology Now thought that each flood event carved a different and new path on its way to the Columbia River Gorge.

32 Model Development/Assumptions Research suggests Grand Coulee-Moses Coulee Floods Telford-Crab Creek Floods Cheney-Palouse Floods This modeling effort attempts to capture the LAST of the Missoula Flood Events

33 Results From Geologic Record: Maximum Lake Missoula Elevation = 4,200 ft 386 million cfs peak (50 Amazon Rivers or 10 times all the rivers in the world combined!) 30 to 50 mph velocities separate Missoula Floods Flood waters reached as far upstream the Willamette Valley as Eugene, OR.

34 Results From the HEC-RAS output: Breach initiation to Pacific Ocean: 48 hours. Peak Discharge at Breach: 141 million cfs 6 days to drain Glacial Lake Missoula. Peak Discharge at Ocean: 32.6 million cfs. 4 days to fill up the Willamette Valley, 14 days to drain. Floodwater traveled 120 miles UP the Snake River, 70 miles UP the Yakima River. Up to 980 ft inundation depths in Glacial Lake Columbia, 690 ft below Dry Falls. 200 ft inundation in Downtown Portland.

35 Results From the HEC-RAS output: Velocities around 65 ft/s found at Wallula Gap, 26 ft/s through the Columbia River Gorge. Flood Depths in the Gorge up to 380 ft. Geologists estimate the maximum to be 980 ft.

36 Results Flow Hydrographs 5.00E+06 Discharge (m 3 /s) 4.00E E E E million cfs Ice Dam Breach 32.6 million cfs Mouth of Columbia 0.00E Days

37 Results

38 Results My HEC-RAS Model Results

39 Results

40 Results Wilson, Lake, and Rock Creek Coulees did not flood in modelgeologic evidence suggests otherwise. This prevented Upper, Middle, and Lower Crab Creek, and Lind Coulees from flooding. Again, geologic evidence suggests otherwise. Shorter breach development times produced slightly higher peak discharges, but not enough to flood the higher elevation coulees. Other knobs: Manning s n values, discharge coefficients, etc. Must be a geomorphic explanation to the differences.

41 Results Wilson Lake Rock Cheney Palouse Floods 41

42 Conclusions HEC-RAS can model an event like the Glacial Lake Missoula Floods This Simulation probably better represented the last of the many Glacial Lake Missoula Floods Much more research into pre-flood sediment deposits/characteristics to run a sediment transport dam breach model

THANK YOU cgoodell@westconsultants.com www.

Cataclysms on the Columbia, Timber Press,

43 THANK YOU Alt, David. Glacial Lake Missoula and Its Humongous Floods, Mountain Press Publishing, Missoula, MT, Allen, John Elliot; Burns, Marjorie, Cataclysms on the Columbia, Timber Press, Portland, OR, Great Overall Resource online collection of erratics.

The Example of the Lake Missoula Flood

Chapter 85 The Example of the Lake Missoula Flood As already noted, uniformitarian hypotheses rarely, if ever, can be supported by extensive geological evidence. Part of this is due to the nature of the