Currently browsing category

floods

Flooding around the world (3 July edition)

Cross-posted at Highly Allochthonous

Here is a brief update on the floods I covered in the last edition of flooding around the world. Note that there has also been flooding in Xiengkoung, Viengtian, Boolikhamxay, and Xayaboury provinces of Laos, as a result of heavy rainfall from a tropical storm; in Russia’s Khabarovsk region (Kiya and Khor rivers), from heavy rainfall; and in the Philippines’ Davao city, from heavy rainfall.

China and the Yangtze River

The U.S. Corps of Engineers increased the output of the Gavins Point Dam spillway to 150, 000 cubic feet per second June 14, 2011. The flow was increased to help regulate the Missouri River due to record snow and rain fall earlier this year. (SDNG photo by Master Sgt. Donald Matthews)

Flow from the Gavins Point Dam spillway was 150, 000 cubic feet per second on June 14, 2011. (SDNG photo by Master Sgt. Donald Matthews, image on Flickr)

Missouri River

The Souris River, continues to flow over Minot, N.D. flood levees June 23, as the water begins to inundate residential neighborhoods. (DoD photo by Senior Master Sgt. David H. Lipp)

The Souris River, continues to flow over Minot, N.D. flood levees June 23, as the water begins to inundate residential neighborhoods. (DoD photo by Senior Master Sgt. David H. Lipp, image from Flickr)

Souris River

Flooding around the world (26 June edition)

Cross-posted at Highly Allochthonous

Since the last edition of flooding around the world, flooding along the Mississippi River has mostly subsided, but flooding continues along the Missouri River and in China. Several new flood wetspots have also popped up, as the image below from The Flood Observatory (at the University of Colorado) depicts.

Current flooding, image from The Flood Observatory (http://floodobservatory.colorado.edu/)

Current flooding, image from The Flood Observatory (http://floodobservatory.colorado.edu/)

The big stories are flooding in China, along the Missouri River, and on the Souris River in Saskatchewan and North Dakota. The best summary I’ve seen is by Jeff Masters of Weather Underground, who gets straight to the story in his headline: “Floods overwhelm North Dakota levees; floods kill 175 in China”. The Flood Observatory also has a handy table that includes flood cause, duration, and a snippet of recent news for each of the flood events pictured on the image above.

TRMM measured precipitation over China, June 13-19, 2011 (NASA image)

TRMM measured precipitation over China, June 13-19, 2011 (NASA image)

China

Flooding continues in central and southern China’s Zhejiang, Jiangsu, Anhui, Jiangxi, Hubei, Hunan and Guangdong provinces, and in parts of the northwest Gansu Province (though drought is still the more dominant threat there).

NOAA Hydrologist Steve Buan just took this photo from Broadway Bridge looking upstream in #Minot, ND  via Justin Kenney on Twitpic

NOAA Hydrologist Steve Buan took this photo on 25 June from Broadway Bridge looking upstream in Minot, ND, via Justin Kenney on Twitpic

The Souris River and Minot, North Dakota

More than 11,000 people have been evacuated and more than 4000 homes inundated in record-breaking flooding in Minot, North Dakota and surrounding communities. Levees in Minot were over-topped, even after emergency preparations by the Corps of Engineers. The river crested yesterday about 2 m above major flood stage, but will remain extremely high for a few more days.

  • Where is the Souris River? It is not part of the Missouri basin. No, as the map below shows, the Souris is part of the Assiniboine River River watershed. The Red River, which flooded earlier this year also drains to the Assiniboine, but the currently flooding Souris doesn’t have the same lake bottom geologic history as the Red.
  • Map of the Souris River and related watersheds, from Wikipedia

    Map of the Souris River and related watersheds, from Wikipedia

  • Why is there flooding?The seeds of the record floods along the Souris and Missouri Rivers were sown beginning last summer, with persistent heavy rains (that lead to flooding), a wet fall, a snowy winter, and then another very wet spring.
  • What’s it like in Minot right now?The city is effectually split in half by the flooding, with 1 in 3 residents is evacuated. It is unclear whether the municipal water supply of Minot and a nearby Air Force base has been contaminated, so the city is under a boil water order. (CNN wire report, 26 June). Residents in unflooded portions of town and surrounding areas are doing what they can to shelter the evacuees and take care of the belongings they got out before the flood arrived. (AP, 26 June)
  • Are there problems anywhere else on the river?Yes, the flood has displaced hundreds in southeastern Saskatchewan, upstream of North Dakota (CBC, 20 June). Floodwaters in that area are now receding (Montreal Gazette, 25 June). Downstream of North Dakota, residents along the Souris River in Manitoba are working to build up their defenses, because the flood will be there in less than two weeks. (Toronto Sun, 25 June). This new flooding arrives on top of already a record-breaking year for floods for the province, with $1 billion in damages already and 3 million acres of farmland still soaked and unplantable (UPI, 22 June).
  • Are there any good pictures of the flooding?The Sacramento Bee had a striking collection of photos on Friday, 24 June. A lot of the news stories linked to above have photos, NASA’s Earth Observatory has an event page with four sets of images so far, and I’d be really surprised if the other big photo news blogs didn’t have a set of images at some point in the next few days.
Holt County Levee District No. 10, a non-federal levee near Rulo, Neb., experienced an overtopping breach June 18, 2011, flooding U.S. Route 159 and the surrounding area. Photo by Diana Fredlund, US Army Corps of Engineers. Image from Flickr.

Flooding from the breach of a non-federal levee near Rulo, Nebraska on 19 June. The levee overtopped and breached on 18 June 2011, flooding U.S. Route 159 and the surrounding area. Photo by Diana Fredlund, US Army Corps of Engineers. Image from Flickr.

Missouri River

Record flooding continues to move downstream in the Missouri River system. Heavy snowpacks and a lot of rain in the Upper Missouri have forced unprecedented releases of water from the dams along the river in the Dakotas. Right now, the biggest flood problems seem to be in Missouri and Iowa, but high water and evacuated areas are stretched all along the river, and the flood won’t fully recede for months. The National Weather Service has a flooding information page set up, with regular updates.

  • How has the flood been affected by the dams along the Missouri River? There’s a lot of public debate over whether the Corps of Engineers management plan for the river favors upper basin states’ desires to keep their reservoirs full over the flood-control needs of downstream states. (KC Monitor, 25 June) People are asking why the Corps didn’t release more water earlier this year, in order to prevent such massive releases now. But, flood prediction models couldn’t have forecast the week after week of heavy rain that fell this spring. Still, I expect people and politicians (especially in the lower basin) to keep talking about this as long as the flood and its cleanup lasts. Here’s an editorial from the Des Moines Register (25 June) that tries to put things in perspective.
  • How are the levees? “A total of four levees in Missouri have been breached along the Missouri River, according to officials with the U.S. Army Corps of Engineers in Kansas City. The epicenter of the flooding in Missouri is located in Holt County, where two levees have been overtopped and two levees have been breached by raging water flowing down from a reservoir in South Dakota. ” (KC Monitor, 25 June) There have also been levee breaches in multiple places on the Iowa side of the river (Reuters, 25 June).
  • What about the nuclear plants? Two Nebraska nuclear plants are in the path of Missouri flood waters, but emergency levees are 0.6 m higher than the expected crest at the Fort Calhoun plant (Omaha World-Herald, 17 June) and 2 m higher than the expected crest at the Cooper station (Chicago Tribune, 25 June). [Update: 6:30 pm 26 June: While I was writing this post, news wires reported than a temporary berm around the Fort Calhoun plant breached last night. Two feet of water now surround reactor buildings, but the reactor systems were unaffected and inside water-tight buildings. (Reuters)] Charmingly, residents near the plants are unconcerned, according to the Chicago Tribune story.
  • What does the flood look like from above? NASA’s Earth Observatory has 9 satellite images of the flood, so far. There’s also a nice video taken on 9 June from a low-altitude airplane, by KETV news.

Open Thread

Please use the comment thread below to add links to updated news stories, videos, or imagery about any floods that are occurring in the next few weeks. I’ll write another flood update in mid-July. If there are particular floods you are interested in, or if you’d like me to delve more into the hydrological details, please let me know.

Anne is a "Strange Quark"

Wow! I won the “strange quark” (2nd place) award in a science writing contest, hosted by Three Quarks Daily, for blogging about the Mississippi River, floods, levees, and the illusion of control.

As I wrote in the comments at 3QD:

Wow! I never thought I’d actually win something for writing about stuff for fun. Thank you to Dr. Lisa Randall for selecting me, the folks at Three Quarks Daily for hosting this contest and boosting me into the finals. I am deeply honored to be a winner of the 3 Quarks Daily contest, and incredibly impressed by the company I’m in.

The 1993 Mississippi River floods were the event that made me become the scientist I am today, so I really wanted to do a creditable job explaining the perspectives and nuances of flood management. Based on the response to the piece, I must have done OK! But now I’ve set myself the goal of bringing that same quality of writing to more blog posts and my scientific papers, so I may be in trouble if they don’t live up to the high praise that this post has gotten.

Thanks to my readers for supporting me in the contest and in blogging generally. Special thanks to my co-blogger Chris for giving me a place to write and for encouraging and supporting me every day.

Flooding around the world (early June edition)

Cross-posted at Highly Allochthonous

Got flood fatigue yet? Too bad, because the wet weather and the high water keeps coming. Here is a quick round up of the notable flood-related news of the week.

High water on the Mississippi River, La Crosse, Wisconsin, 21 April 2011

Front row seats for water levels above flood stage on the Mississippi River, La Crosse, Wisconsin, 21 April 2011

Mississippi River

Floodwall (with emergency height added) in Omaha, Nebraska during the record 1952 floods.

Floodwall (with emergency height added) in Omaha, Nebraska during the record 1952 floods. Will that record be broken this year? (Image from Nebraska DNR.)

Missouri River

Heavy snowpacks in the Missouri River watershed (an areally large, but volumetrically smaller contributor to the Mississippi) have led to near-record flooding that is on-going along its whole length from Montana to Missouri. It’s not getting as much media attention as the Mississippi River, but water levels may stay above flood stage for months. Right now there are heavy rains occurring in parts of the basin, with more rain in the forecast, which will only add to flood problems.

Like the Mississippi, the Missouri is heavily managed by the Corps of Engineers, which is taking some criticism for residents in affected cities. There have also been evacuations because of seepage under levees and concerns about the possibility of failure. Like all big river/developed world flood stories, this one is a complicated mix of huge volumes of water, complicated multi-purpose river management plans, and unwise historical floodplain development.

  • In Historic Flooding On Mississippi River, A Missed Opportunity To Rebuild Louisiana:
    http://www.huffingtonpost.com/2011/06/09/in-historic-flooding-on-m_n_873623.html
  • Flooding from heavy rain in Guizhou province, southwestern China on 6 June 2011 (photo: Xinhua)

    Flooding from heavy rain in Guizhou province, southwestern China on 6 June 2011 (photo: Xinhua)

    China

    For months, China has been stricken by its most intense drought in 60 years, but right now it’s too much, not too little, water that is the problem. Flooding since the 1st of the month has affected East China’s Jiangxi Province and 12 provinces in central and southern China, and more rain is in the forecast for many areas. Intense rains over the last few days have caused the evacuation of more than 100,000 people and killed at least 54.

    Elsewhere

    The Flood Observatory is also reporting on-going flooding in Colombia, the Philippines, Algeria, Haiti and the Dominican Republic, Canada, India, and Upstate New York/Vermont’s Lake Champlain area. In every one of these places, people are losing their homes and lives. While volcanoes and earthquakes shake things up spectacularly now and again, every single day, somewhere in the world, there’s a devastating flood going on.

    Lingering flooding along the Middle Mississippi River and tributaries

    Cross-posted at Highly Allochthonous

    NASA MODIS image of flooding along the Middle Mississippi, 20 May 2011

    Figure 1. NASA MODIS image of flooding along the Middle Mississippi, 20 May 2011.

    One week ago today (28 May 2011), I had the chance to explore the lingering flooding along the Mississippi River and its tributary Big Muddy River in southern Illinois. The area was long past its crest; it is upriver of Cairo and the Birds Point Floodway. Around Carbondale, evidence of the recent high water was still visible in all of the drainages, but the water was back well within the stream banks. Closer to the confluence with the Mississippi though, high water levels on the Mississippi were still forcing backwater flooding of the floodplain and the Big Muddy River.

    Driving and hiking along the escarpment of the LaRue-Pine Research Natural Area afforded expansive views of the flooding – and the remnant landscapes of previous millenia of river activity.

    Foreground: An abandoned channel remains as a wetland. Background: Levees and flooding along the Big Muddy River.

    Figure 2. Foreground: An abandoned channel remains as a wetland. Background: Levees and flooding along the Big Muddy River. (Click for larger version)

    Flooding along the Big Muddy River, 28 May 2011

    Figure 3. Flooding along the Big Muddy River, 28 May 2011 (Click for larger version)

    Once we descended from the hills and onto the floodplain, we were immediately greeted by floodwaters.

    Flooded bottomlands

    Figure 4. Flooded bottomland forest along the Big Muddy River.

    Driving away from the hills towards the Mississippi, our road took us along the top of the levee, giving us close up views of the effects of leveeing, levee repairs, and local wildlife.

    Big Muddy inside the levee

    Figure 5. A barn and fields protected from flooding by the levee on which we drove. (View out the window on the south side of the car.) (This barn is visible in the middle left of Figure 3).

    Big Muddy outside the levee

    Figure 6. The Big Muddy River, in flood, contained by the levee we drove along. (View out the window on the north side of the car, immediately opposite Figure 5.)

    Levee repair along the Big Muddy

    Figure 7. Temporary levee repair along the Big Muddy. The plastic sheeting and sandbags may be covering an area that had cracked or started to erode (click for larger).


    Snapping turtle

    Figure 8. Why did the snapping turtle cross the levee road?

    After crossing the Big Muddy River, we drove along a state highway that was not atop a levee, and only a few feet above flooded fields. Egrets and herons were everywhere in the standing water, and a pleasant breeze whipped up waves on the water. But we were reminded that this scene was normally not so watery…in the image below, you might be able to see a center pivot irrigation line in the field, standing in the flood waters.

    Flooded fields and an irrigation line

    Figure 9. A flooded field, with an irrigation line. Normally, this landscape would not be so blue. (Click for larger)

    Finally we reached the Mississippi itself, in Grand Tower, Illinois. The river was definitely high, but open for business – we watched a tow and barges go by. The town of Grand Tower is situated immediately adjacent to the Mississippi – and protected by a big levee. Near the north end of town, the levee was a few feet lower than the rest, and here a metal floodwall had been constructed atop the levee. There was also evidence that a pumping operation had been set up – to pump water from behind the levee back into the river. Whether this pumping was necessitated by seepage or localized ponding, I couldn’t tell. But here, in a sleepy little town on the Mississippi, the effects of our efforts to keep floodwaters off the floodplain were in full display.

    Pumping set up and a floodwall atop a levee

    Figure 10. A pumping and a floodwall atop a levee (on right side of photo) in Grand Tower, Illinois.


    Mississippi River flooding, Grand Tower, Illinois

    Figure 11. Mississippi River flooding, Grand Tower, Illinois. Looking downstream, with a levee on the left side of the image.

    Anne in the news

    Flooding along the Mississippi River
    Last week, I wrote a post for the Scientific American Guest Blog on “Levees and the Illusion of Flood Control,” about the ways that while levees around individual communities may be good, the systematic leveeing of entire waterways is a bad long-term strategy. On Friday, that post was also featured on the front page of ScientificAmerican.com on their Science Agenda. (I’ll add a screenshot if I can dig it back up.)

    Linkages between climate change and severe weather
    This morning my name may be in your local newspaper, as I’m quoted in an article about how this spring’s severe weather (including flooding along the Mississippi) fits with scientific expectations about climate change. The article was written by the McClatchey syndicate and versions of it may appear in multiple newspapers. For example, here’s the Charlotte Observer’s version of the story.

    Flooding along the Mississippi River

    Cross-posted at Highly Allochthonous

    In case other events have crowded it out of your news feed, there’s record-breaking flooding going on in the Mississippi River basin. Snowmelt in the headwaters, combined with weeks of heavy rains in the middle reaches of the river basin, have pushed the system to its engineered limits. The Mississippi River basin is home to more than 100 million people, and when the water flows past Natchez, it’s carrying flow from 41% of the contiguous United States, making it the third largest river basin in the world. The volume of water carried by the Mississippi River in flood can be measured in the same unit as ocean currents — within the next few days, the Mississippi River at Natchez will be flowing more than 2 Million cubic feet per second.

    Flooding at the junction of the Mississippi and Ohio Rivers, 3 May 2011, NASA image

    Flooding at the junction of the Mississippi and Ohio Rivers, 3 May 2011, NASA image

    Start here

    For hands-down the best analysis on the flooding, the engineering, the politics, and the media coverage of the flooding, you need to turn to Steve Gough’s Riparian Rap blog. Go there now to get caught up. Then when you want some other perspective, check out the links and resources below.

    General information on the flooding

    Floodways doing what they were designed to do

    Edge of the inflow section, Bird's Point floodway. image by the US Army Corps of Engineers

    Edge of the inflow section, Bird's Point floodway. image by the US Army Corps of Engineers


    Early in the week the big Mississippi news story was on the opening of the Bird’s Point Floodway in Missouri. Media reports tended to focus on the sensationalist “us vs. them” people stories, with most of the stories completely missing the fact that the floodway was designed for this purposes and residents in it had known about and been compensated for its existence. Steve Gough had great coverage, including this piece.

    The next big to-do will be over opening the Morganza floodway in Louisiana, expected to happen on Thursday 12 May. So far, the news media seems to be taking a bit more reasonable perspective here, but I expect there will be hysterical stories as well. My two cents: Based on experience with devastating past Mississippi River floods, our national policy has been to design and designate floodways to relieve pressure on levees on the mainstem of the Mississippi River. This means that some people miles from the main river will lose homes and property (and have been compensated for that risk), but it is for the benefit of much larger populations. Further, the areas that lie in floodways are part of the natural floodplain of the Mississippi River, and they would flood much more frequently without the levees.

    More information on Bird’s Point and Morganza floodways can be found below.

    Background Reading

    1927 Mississippi River flooding, image from the Library of Congress

    1927 Mississippi River flooding, image from the Library of Congress


    The best general background information on floods and flood control on the Mississippi River can be found in John M. Barry’s book “Rising Tide: The Great Mississippi River Flood of 1927 and how it Changed America” and John McPhee’s essay on the Old River Control Structure in The Control of Nature, available on-line through The New Yorker.

    Floodwaters rising on the Red River

    Cross posted at Highly Allochthonous

    Fargo, North Dakota is coming out of its 3rd snowiest winter since 1885. Snow continued to fall into late March, and daytime temperatures have only been above freezing for few weeks. At night, it’s still below freezing, though starting tomorrow night the forecast calls for above freezing minimum temperatures. Soils are already saturated, and more rain is possible this weekend.

    In short, it is perfect flood weather for the Red River that runs along the Minnesota-North Dakota border and into Canada. This is a place with the perfect geography for extensive flooding, and a long history of big spring floods.

    Checking the water level on a bridge between Fargo and Moorhead. Photo from Minnesota Public Radio.

    Checking the water level on a bridge between Fargo and Moorhead. Photo from Minnesota Public Radio.

    Every town along the Red River has been devastated by a flood more than once. So they’ve all got emergency response plans in place for weather just like this. For example, Moorhead (Minnesota, across the river from Fargo) has a nifty GIS feature that shows how each foot of flood water affects each city block.

    Residents are already filling sand-bags to build temporary levees. But with year after year of flooding, and with successful sand bag efforts the last two years, some residents might be taking this year’s flood predictions in a somewhat complacent fashion. But looking at the National Weather Service’s North Central River Forecast Center projections, there’s plenty of reason for concern all along the Red River.

    As of 9 am Central time on 7 April 2011, most of the US portion of the Red River is already above flood stage, but water levels will continue to rise almost everywhere for at least the next week.

    Flood stages as of 9 am 7 April 2011. Screen grab from NCRFC.

    Current flood levels along the Red River and nearby drainages, as of 9 am, Thursday 7 April 2011. Orange circles indicate minor flooding, red indicates moderate flooding, purple indicates major flooding. Screenshot from the North Central River Forecast Center, using data supplied by the USGS.

    The flood wave will move downstream – from south to north. In Wahpeton, a crest is expected today, with a second – equally high if not higher – crest next week. There the flood crest is likely to fall a few feet short of record water levels set in 1997.

    Between Wahpeton and Fargo, tributaries to the Red River are having major flooding as well – in part because of backwater effects from the main river. If the Red River is flooding, there’s no place for water flowing down the tributaries to go. Instead they back up, causing even more widespread flooding.

    In Fargo (ND) and Moorhead (MN) – which have a combined population of 200,000 people – the flood will not crest until late Sunday. Right now, the National Weather Service is predicting a crest of 39.5 feet, which 1.3 feet short of the record flooding of 2009. However, there some chance that the river will crest at 41 feet, or even higher if there is precipitation in the next few days. Currently, 80% of the city is protected by sand bags and levees to a height of 41 feet, but those may need to go even higher.

    NWS Flood Forecast for Fargo, North Dakota (7 April 2011)

    NWS Flood Forecast for Fargo, North Dakota (7 April 2011)

    Two weeks ago, the National Weather Service issued a longer-term flood forecast for the Red River at Fargo. At that time they considered it a 10-50% percent chance that the river would reach 40 to 44.3 feet by mid-April. They provided a probability of exceedence curve for their modeled projections of this year’s flood season against the historical record of flooding, as shown below. To understand this graph, it helps to look at a few specific points. Right now, the river is at 35.32 feet. Based on the outlook from two weeks ago, it was virtually inevitable that the river would reach this level, with a probability greater than 98%, as shown by the black triangles. In contrast, 35.32 feet is reached less than 5% of the years in the historical record for Fargo, as shown by the blue circles. The current projected crest of 39.5 feet was given about a 50% chance of being exceeded as of two weeks ago, yet it has only be reached twice (1997, 2009) in 111 years of record. Two weeks ago, the National Weather Service was saying that there was a 25% chance the river could go above 42 feet, which is higher than the top of the sand bag levees now being prepared.

    NWS Chance of exceeding river levels on the Red River at Fargo, conditional simulation based on current conditions as of March 24, 2011

    NC River Forecast Center's 90 model showing the Red River at Fargo's chances of exceeding certain water levels, relative to the historical record.

    The short term forecasts, like the one two above, have better skill than long term forecasts like the immediately above, but the long term forecasts are vital for emergency managers, city officials, and riverside land-owners in making early plans for the flood. The reason they’ve got all the sand and sand bags on hand in places like Fargo is because they knew there was a good chance a really big flood was coming. They’ve been talking about it since January.

    Downstream (north) of Fargo-Moorhead lies Grand Forks, with about 100,000 people in its metropolitan area. Grand Forks was swamped by the flood of 1997, but the current forecasted peak stage this year is about 3.5 feet lower, though the crest won’t reach Grand Forks until late next week. For now, they are watching the water levels and making their preparations. Downstream further, lies Winnipeg, Manitoba. The flood crest won’t reach there until late April, but already the river is 17 feet above normal winter stage, and only 5 feet below the 2009 flood peak. Needless to say, they too are sand-bagging.

    But for the next few days, the action focuses on the Fargo-Moorhead area. You can check out the updated data and forecasts or you can watch the flood play out in Moorhead with a live webcam pointed at the downtown waterfront:
    http://www.justin.tv/widgets/live_embed_player.swfWatch live video from 702 Flood Cam – Moorhead on Justin.tv

    A continental divide that runs through a valley

    Now that’s pathological.

    Parts of the Upper Midwest are disappearing under spring floods. The Red River of the North is at major flood stage, again, and the Minnesota River flood crest is moving downstream. It’s a pretty frequent occurrence in both of these river systems, and in part, flooding is a legacy of the glacial history of the area. The Red River flows to the north along the lake bed of Glacial Lake Agassiz, which is pathologically flat. The Minnesota River flows to the south along the channel of the Glacial River Warren, which was gouged out of the landscape by water draining from Lake Agassiz.

    14,000 years ago there was direct connection between what is now the Red River basin and the Minnesota River basin. Today, there’s a continental divide – with the Red flowing toward Hudson Bay and the Minnesota flowing toward the Mississippi and Gulf of Mexico. But what a strange continental divide it is – for it runs through the former outlet of Lake Agassiz, in what is now known as Brown’s Valley or the Traverse Gap. This divide is not so much a high point in the landscape, but a just-not-quite-as-low area. The little community of Brown’s Valley sits between Lake Traverse (flows to the North, forming the headwaters of the Red) and Big Stone Lake (flows to the south, forming the headwaters of the Minnesota).

    Here’s what it looks like on Google Earth. Note that I’ve set the terrain to 3x vertical exaggeration, so that you have some hope of seeing the subtle topography of this area.

    Croppercapture12

    And here’s a very, very cool oblique photo from Wikipedia. It shows the divide looking from north to south — mostly covered by floodwaters in 2007. It’s not every day you get to see a continental divide covered in water.

    800px-browns_valley_flood_07

    Why does the Red River of the North have so many floods?

    Cross-posted at Highly Allochthonous

    Communities along the Minnesota-North Dakota border are watching the water levels, listening to the weather forecasts, and preparing for another season of flooding. It must be a disconcertingly familiar routine, as this will be the third year in a row in which the Red River of the North reaches major flooding levels. But this isn’t merely a run of bad luck for residents in the Red River Valley, major floods are to be expected in a place with an unfortunate combination of extremely low relief and a river at the whim of snowmelt and ice jams.

    The Red River of the North begins in Minnesota, near the border with North and South Dakota, and it flows northward through Fargo/Moorhead, Grand Forks, and Winnipeg before emptying into Lake Winnipeg, Manitoba. The landscape around the Red River is excruciatingly flat (Figure 1), for the Red River Valley isn’t a stream-formed feature at all, but is the remnant landscape of Glacial Lake Agassiz, which held meltwaters from the Laurentide Ice Sheet for more than 5000 years. The modern Red River has barely managed to incise into this flat, flat surface, because it slopes only very gently to the north (~17 cm/km). Instead, the river tightly meanders across the old lake bed, slowly carrying its water to the north. Topographically, this is a pretty bad setting for a flood, because floodwaters spread out over large areas and take a long time to drain away.

    Topography of the US portion of the Red River Valley from SRTM data as displayed by NASA's Earth Observatoryredriver_srtm_palette

    Figure 1. Topography of the US portion of the Red River Valley from SRTM data as displayed by NASA's Earth Observatory

    The climate of the Red River watershed makes it prone to flooding during the spring, usually peaking in about mid-April. The area receives about 1 m of snow between October and May, and the river freezes over. In late March to early April, the temperatures generally rise above freezing, triggering the start of snowmelt. Temperatures warm soonest in the southern, upstream end of the watershed and they get above freezing the latest near the mouth of the river. This means that snowmelt drains into the river’s upper reaches while downstream the river is still frozen, impeding flow (Figure 2). As the ice goes out, jams can temporarily occur and dam or back up the river, exacerbating local flooding problems.

    Red River near Oslo, Minnesota, 3 April 2009, photo by David Willis

    Figure 2. Red River near Oslo, Minnesota, 3 April 2009. Here the main river channel is still clogged with ice, while surrounding farmland is underwater. Photo by David Willis of http://www.cropnet.com/.

    Together the topography and climate of the Red River watershed are a recipe for large-scale flooding, and the historical record shows that floods are a frequent occurrence on the river. Usually, hydrologists talk about rivers in terms of their flow, or discharge, which is the volume of water per second that passes a point. But, when talking about floods like those on the Red River, it’s not so much volume that matters as how high the water rises (“stage”). The National Weather Service is responsible for flood prediction in the US, and they define flood stage as “the stage at which overflow of the natural streambanks begins to cause damage in the reach in which the elevation is measured.” If the water level continues to rise, “moderate flooding” occurs when “some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations are necessary.” Further increases in water levels can bring a river to “major flooding“, when “extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.” That’s the sort of flooding that will happen in places along the Red River this spring, as it has many springs in the historical record (Figure 3).

    Annual peak stage on the Red River at Grand Forks, North Dakota

    Figure 3. Annual peak stage on the Red River at Grand Forks, North Dakota. Data replotted from the USGS, with local NWS flood stages shown.

    Already, flood warnings are being issued for the Red River and its tributaries. As I’ll discuss in my next post, the long-range forecast for this spring’s floods on the Red is looking pretty grim. But as the communities along the river brace for the on-coming flood, it is important to remember that the geology and climate of the region make repeated major floods inevitable.