Significance of Snowmelt and River Ice on Flood Damages

1. Meredith Carr Research Hydraulic Engineer Cold Regions Research and Engineering Lab, Hanover, NH Missouri Basin River Forecaster’s Meeting 21 February 2013 Significance of Snowmelt and River Ice on Flood Damages

2. Objective • Flood Risk Reduction Mission • Feasibility and cost benefit analysis of flood control projects • Management of existing projects • Development of tools and theories related to predicting and designing for cold regions flooding • Quantify the significance of snowmelt, rain-on-snow and river ice related flooding • Property and crop damages • Injuries/loss of life

3. Background • 94 million acres of land in US estimated at risk for flooding • ¾ of presidential disaster declarations associated with flooding • Annual average of $6 B damages and median of 81 lives lost (2006, 2008 studies) • Increase in flooding impact due to urbanization and coastal development

4. Snowmelt Floods • Factors affecting flood severity: • fall soil moisture condition • ground frost • water content of snow • speed of melting • presence of heavy rain • Particular concern in Northeast, north central and eastern US, also downstream in large drainage basins • 8 of 32 most significant floods of 20th century were related to snowmelt (Perry, 2000)

5. Snowmelt Floods Accumulated annual snowfall divided by annual runoff. Red lines indicate areas where streamflow is snowmelt dominated (Barnett et al, 2005)

6. Fig 4: Sites with Rain-on-Snow Events from 1949-2003 (McCabe et al., 2007) Rain on Snow Floods • Common in the Pacific Northwest, but also in other areas • Rain provides energy to melt the snow, releasing water and increasing runoff

7. Ice Jam/Action Floods • ice cover breaks into large pieces which move downriver and elevate water levels or form a jam • freezeup jams, which occur as ice forms dynamically at the onset of cold temperature, can cause long term flooding

8. Fig 7: Explosive Remnants on the Missouri River Ice Jam, March 2009 (Stromme, 2009) Ice Jam/Action Floods Yukon River near Eagle, AK, 2009 Skunk River near Augusta, IA, 2010

9. Data and Analysis • Data sources (2001-2010): • Flood events from the National Climatic Data Center Storm Events Database • CRREL Ice Jam Database • Snow water equivalent gridded data based on SNODAS data • USGS gages along major snowmelt rivers • Weather Review Journal articles

10. Fig 11: Percent of Flooding Damages Due to Snowmelt or Ice by Sub-Region Results • Damages due to snow and ice related flooding were most significant in Northern cold and snowy areas, but also extended to downstream areas such as the lower Mississippi River basin

11. Fig 13: Percent of Flooding Damages Due to Snowmelt or Ice by Corps district. Blue Circles Represent Flood Control Dams Results • Snow and ice related flood damages, by Corps District • Most significant damages in the New England District, the Mississippi Valley Division and the Northwest Division. • Rain-on-snow events are common in the Northwest, contributing to the over 50% of flood damages due to snowmelt or ice in the Sacramento District.

12. Results Percent of Flooding Damages Due to Snowmelt or Ice

13. Results Total Property and Crop Damages 2001-2010

14. Results

15. Results • Snow and ice related flooding • contributed to 42% of flood events during the 10 year period • 48% of damages, 22% of fatalities, 10% of injuries • Event length of 3.1 d • Snowmelt: 4.3 d, Ice action: 2.9 d, • Ice Jams: 2.1 d, Rain-on-snow: 1.8 d

16. …..Discussion….. Sunday, March 22, 2009 in Fargo (AP Photo/The Forum, Dave Wallis)