Boulder Flooding - Could it Happen Here?

Everyone has been following the tragic events as a result of the Flash Flooding in and around Boulder, Colorado. The rain event shattered daily records, has resulted in enormous amounts of damage, untold heartache and the ultimate, unfortunate loss of life. It will take quite some time for the area to fully recover, and even longer to fully assess what happened.

Residents of the Red River Valley are no stranger to flooding on a similar, but very different magnitude. Spring snow-melt floods have displaced tens of thousands, caused billions of dollars in damage, and are still  topics of discussion today. Planning for the next great flood is ongoing, and mitigation projects will be underway for years to come. Although the largest floods have been spring snowmelt induced, the greatest in modern history - 1997 and 2009 - had a component similar to the Boulder flood.

Thunderstorms.

Excessive rainfall during a critical melt period in 1997 devastated the Wahpeton / Breckenridge area and ultimately lead to the flooding of Grand Forks/East Grand Forks. Thunder-snowstorms in March 2009 nearly cost Fargo the spring flood battle. And throughout the recorded history of the Red River Valley thunderstorms have caused flooding resulting in significant damage, interrupted livelihoods and more. Could an event such as a Boulder flood happen here?

Obviously, the most significant difference between Colorado and eastern North Dakota/northwest Minnesota is the terrain. Immediately west of the Boulder area the terrain rises sharply, several thousands of feet in a relatively short distance. There are numerous well defined rivers that are well channeled by the terrain, so that water is focused into fast flowing currents. The impervious nature of the terrain accounts for virtually no absorption, meaning that pretty much all the rain that fell ran into the rivers and streams upland of the Boulder area.

Obviously, the Red River Valley is much flatter than eastern Colorado, and with few exceptions heavy rains rapidly accumulate and pond over very large areas. Within the Grand Forks NWS area of responsibility, the Pembina Gorge and escarpment, as well as portions of the Red River Valley beach have sharp enough terrain to cause rapid runoff. In fact, there is a section of the Red Lake River between Crookston and Huot where intermittent Class I or Class II rapids exist, with high enought flows (Source Minnesota DNR).  It was the effects of the western beach of the Red River Valley that exacerbated the major flooding of March 2004 across portions of Pembina, Walsh and Grand Forks counties. Similarly, the same minor terrain changes deeply modified the flows of the June 2000 flood. So, while it is not very likely that terrain would cause a Boulder-type flood, could it happen here?

Yes.

Excessive rainfalls do occur within the Red River Valley as previously noted. Since 1993, the frequency and intensity of these floods has increased for a variety of reasons. Land use management, rural and urban development, saturated soils and more have contributed to the increased frequency and severity of flooding. Below is a table of the official top 25 one and two day rain totals for cities within the Grand Forks County Warning Area. These data are from Official NWS Cooperative Observers, Airport Locations and more recently CoCoRaHs Observers. (Click here for a more complete listing)

1 day record rain totals    
City State Type Total Date
FOSSTON MN COOP 8.97 July 19, 1909
RED LAKE INDIAN AGCY MN COOP 8.20 July 12, 2000
THIEF RIVER FALLS 2 MN COOP 8.12 August 20, 2000
LITCHVILLE 2 NW ND COOP 8.10 June 29, 1975
ABERCROMBIE ND COOP 7.50 June 17, 2009
THIEF RIVER FALLS MUNI AP MN WBAN 7.50 May 29, 1949
GRAFTON ND COOP 7.42 September 2, 1957
LARIMORE ND COOP 7.41 September 2, 1957
ENDERLIN 2W ND COOP 7.18 June 29, 1975
AGASSIZ REFUGE MN COOP 7.03 August 2, 1964
PEMBINA ND WBAN 6.83 May 30, 2010
VALLEY CITY 2.0 NW ND CoCoRaHS 6.78 June 21, 2013
PARK RAPIDS MUNI AP MN WBAN 6.75 August 1, 1906
DEVILS LAKE MUNI AP ND WBAN 6.68 June 24, 2002
LAKE PARK 6.0 S MN CoCoRaHS 6.68 June 21, 2013
THORHULT MN COOP 6.50 August 1, 2001
MOORHEAD MN COOP 6.38 July 16, 1993
HILLSBORO 3 N ND COOP 6.38 July 21, 1987
DILWORTH 7 NNE MN COOP 6.31 July 15, 1993
COOPERSTOWN ND COOP 6.30 July 25, 1993
MAYVILLE ND COOP 6.26 July 22, 1987
SHEYENNE 6.8 ESE ND CoCoRaHS 6.02 August 13, 2011
MC LEOD 3 E ND COOP 6.00 June 10, 1931
LISBON ND COOP 6.00 September 12, 1978
2 day record rain totals    
CAMP NORRIS DNR MN COOP 10.81 June 11, 2002
LITCHVILLE 2 NW ND COOP 10.28 June 30, 1975
LARIMORE ND COOP 9.81 September 2, 1957
WARROAD MN COOP 9.12 June 11, 2002
FOSSTON MN COOP 8.97 July 20, 1909
PARK RAPIDS MUNI AP MN WBAN 8.62 July 18, 1985
BAUDETTE MN COOP 8.45 June 11, 2002
RED LAKE INDIAN AGCY MN COOP 8.20 July 13, 2000
THIEF RIVER FALLS 2 MN COOP 8.12 August 21, 2000
THIEF RIVER FALLS MUNI AP MN WBAN 8.03 May 30, 1949
GRAFTON ND COOP 8.01 September 2, 1957
BAUDETTE INTL AP MN WBAN 7.64 June 10, 2002
THORHULT MN COOP 7.60 August 1, 2001
ENDERLIN 2W ND COOP 7.55 June 30, 1975
RED LAKE FALLS MN COOP 7.54 June 10, 2002
MAHNOMEN 1 W MN COOP 7.50 September 2, 1973
ABERCROMBIE ND COOP 7.50 June 18, 2009
AGASSIZ REFUGE MN COOP 7.42 June 10, 2002
MOORHEAD MN COOP 7.31 June 20, 2000
HILLSBORO 3 N ND COOP 7.27 May 30, 1909
PEMBINA ND WBAN 7.26 May 30, 2010
MAYVILLE ND COOP 7.20 August 20, 1918
COOPERSTOWN ND COOP 7.03 July 25, 1993
HALSTAD MN COOP 6.88 July 23, 1987
COOP = Official NWS Station    
WBAN = Airport Location    

CoCoRaHS = Community Collaborative Rain, Hail and Snow observer

Data above courtesy of the ACIS system  

 

The need for more information

Looking at the data above we see some pretty significant 1 and 2 day totals for our area. While the Doppler radar does a decent job at estimating rainfall, it is far from perfect. Not only that but the heaviest rainfalls may not occur over a rain gauge. The June 2000 Turtle River Flood event, which resulted in several deaths and almost devastated Manvel, was centered south and west of the city of Larimore. Although the 2 day total for Larimore in June 2000 was 8.50 inches - most of that falling the night of June 12th - the highest 2 day total for Larimore is 9.81 inches which fell on September 1st and 2nd 1957. Additionally, the 8.50 inches of rain that fell in Larimore is similar to what happened in the Boulder area to create the most recent floods. (Doppler radar estimates showed that nearly 17 inches of rain fell along the Turtle River in June 2000, but was never verified. That 17 inch rainfall estimate is similar to what fell in the Boulder area over the past 7 days.)

Fargo/Moorhead have experienced pretty significant flooding several times since the wet cycle started in 1993. During the evening into early morning of July 15/16 1993, 5.15 inches fell at Hector Field. Widespread flooding struck the F/M area.

Again, the F/M area was struck with heavy rains. Late in the day into the early morning of June 19/20 2000, 6.82 inches fell at Hector Field, with higher amounts reported causing major damage to the FargoDome and throughout the city.

June 25th and 26th 2013 saw a relatively paltry 3.96 inches of rain at Hector Field with widespread flooding again in town.

These events, and many others, highlight the real threat for flooding rains in our area. With the last 20 years consistently seeing above median rainfall, flooding remains a risk despite the ongoing drought. According to the most recent climate change research, the past 20 wet cycle may actually be the new normal, and the summer droughts of 2012 and 2013 are simply part of the natural variability in climate.

CoCoRaHS is part of the solution

The process to categorize the flood in Boulder will take months, perhaps years of study and analysis. Much in the way the Red River flooding is under continous study, part of that study is looking at the precipitation records; making estimates of how likely rain or snowmelt floods are to occur, and the frequency of heavy rainfalls. All this revolves around data, and CoCoRaHS has proven to be a valuable program in that process. Information received from CoCoRaHS observers helped to define the scope of the event and will be used in an analysis of it.

The importance of accurate and timely data from sources such as CoCoRaHS and the NWS Cooperative Observer cannot be understated. It is a crucial component in the analysis of weather and climate.

While the number of CoCoRaHS observers continue to grow in our area, we can certainly use more. If you are already an active member of the CoCoRaHS family we cannot thank you enough. Your data are used to help us define the current drought, and how it is changing. When the inevitable occurs - the return of heavy rains and snows - having all the reports we can get will help us help you. Otherwise, please consider becoming a CoCoRaHS Observer, and help us keep track of the weather. For more information on CoCoRaHS click here.

 Mark Ewens, Climate Services Focal Point 701.795.5198

 



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