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March Meanderings

Cross-posted at Highly Allochthonous

It all began at the end of February, when I travelled to La Crosse, Wisconsin to the Upper Midwest Stream Restoration Symposium, which was a really stimulating and vital mix of academics, consultants, and government folks all interested in improving the state of the science and practice of stream restoration. I gave a talk on Evaluating the success of urban stream restoration in an ecosystem services context, which was my first time talking about some hot-off-the-presses UNCC graduate student research, and I learned a lot from the other speakers and poster presenters. While the conference was incredibly stimulating, travel delays due to bad weather on both ends of my trip made for a somewhat grumpy Anne (nobody really wants to spend their birthday stuck in a blizzard in O’Hare), so I’ll be thinking carefully about how to plan my travel to the Upper Midwest during future winters. Nonetheless, the view from the conference venue was phenomenal.

icy river and snowy land

View of the Mississippi River from the Upper Midwest Stream Restoration Symposium in La Crosse, WI. Not shown: bald eagles that frequent the open water patches of the river.

March proper saw me give variations of the restoration talk two other times. On the 15th, I gave it as the seminar for Kent State’s Biological Sciences department, and on the 26th, I gave it at the North Dakota State University Department of Geosciences (more about that trip below). In between, I gave a seminar on the co-evolution of hydrology and topography to the Geology Department at Denison University in Granville, Ohio. Students in that department had just returned from a trip to Hawaii, and a very memorable dialogue occured in the midst of me talking about the High Cascades:

“You’ve seen a young lava flow. What would happen if you poured a bottle of water on it?” “It would steam!” “Not that young!”

Closer to home I also hosted a couple of prospective graduate students, helped interview candidates for a faculty position in our department, and went with a colleague to visit an acid mine drainage site about an hour to the south of Kent. In one fairly small watershed, we were able to tour a number of different remediated and unremediated sites, and it certainly lent a whole different perspective to the ideas of stream restoration and constructed wetlands to look at a landscape irrevocably scarred by mining activities.

Orange water flowing from a tube down a hill and into a stream.

Unremediated acid mine drainage flow directly into Huff Run. The orange is iron precipitate.

Wetland plants and a concrete inlet weir.

Constructed wetland as the second stage of acid mine drainage remediation in the Huff Run watershed.

At the end of the month, we finally got our turn for spring break. I ended up with a somewhat epic combination of mounds of work and a big trip to take, possibly the worst combination of the untenured and tenured professor spring break stereotypes (see this PhD comics strip). The first half of the week, I spent in Fargo, North Dakota, home to the famously flood-prone Red River of the North. (I’ve blogged before about why the river so often produces expansive floods.) It was truly fascinating to put my feet on the ground in a place that I’ve read about and watched from afar for years. And my visit was made all the more interesting by my host and guide, Dr. Stephanie Day, a geomorphologist newly at NDSU and who may well unravel some of the Red’s geomorphological peculiarities.

Scientist in foreground, river in midground, background = flat, snowcovered ground.

Stephanie Day, Assistant Professor of Geosciences at North Dakota State University beside the Red River in Moorhead Minnesota. The flat surface in the background is the approximate elevation of the land for miles around.

Looking towards downtown Fargo, ND from the river side of the levee.

Looking towards downtown Fargo, ND from the river side of the levee.

snow and ice covered river, not in much of a valley.

River’s edge view looking towards downtown Fargo. Snow well over knee deep here on 25 March, by my measurements. As all that snow starts to melt, the water will rise.

There’s a pretty good chance we’ll see a major flood on the Red River later this spring, as the >24″ of snow melts out of the watershed, runs off over frozen ground, and enters the northward flowing river. The Fargo Flood page is the place to go to follow the action, and you can count on updates (and more pictures) here as events unfold.

The latter half of my spring break saw me diagonal across the state of Minnesota to my beloved Driftless Area, back across the Mississippi River, and into the state of Wisconsin. I saw my family, finished paper revisions, and wrote part of a grant proposal. Then I flew home, with nary a weather delay in sight.

If March was a tight, recursive meander of talks and trips to the Upper Midwest, then April promises to be a bit anastomosing with lots of different threads woven together to make another month of scientific delight.

After the storm

Cross-posted at Highly Allochthonous

It’s been quite a week. My home in northeastern Ohio got off lightly from “Superstorm” Sandy, compared to places closer to the Atlantic seaboard and in the Caribbean. But still, over 250,000 people lost power due to high wind, especially in Cuyahoga and Lorain counties along the shores of Lake Erie, where huge waves also caused closure of an interstate and damage. Power crews are still working to restore power to tens of out thousands, and most schools and universities were closed for at least one day, if not longer.

NewsChannel5 photo of large waves crashing against shore in foreground, smokestacks in background

Waves from Sandy crashing against the Lake Erie shoreline in Cleveland. Photo from News Channel 5. Click image for link to source.

Large tree fallen in front of house.

A tree down in my neighborhood, which took the branch of another one as it went. This same picture was the one featured on the local paper’s website story about storm damage. Does this mean it was the most dramatic tree to fall in Kent? Whether or not it was, these people got lucky the trees fell away from their house.

There was also some rain. At my house, I got 4.25 inches (108 mm), which is almost exactly what the forecasts predicted. It came as both a drizzle and as heavy rains, but since last Friday afternoon we haven’t seen the sun. Now, northeastern Ohio is supposed to be quite cloudy, but given the local grumbling, this might be a bit of an extraordinary gray and damp cold run. It wasn’t warm rain either, with temperatures neither climbing out of the 40s F (8 C) or dipping below freezing. Isotopic results are pending, but my money is on our moisture source being almost entirely that northern airmass that got itself entangled with the tropical cyclone. Again, any whining about the damp is pretty well offset by everyone acknowledging that we are extremely lucky compared to states to our east.

All that cold rain brought the local river levels way up. There was major flooding on the Cuyahoga River at the downstream end by Wednesday, and the river at its upstream-most gage in Hiram crested on Thursday night. Flow at Hiram peaked around 1900 cubic feet per second (53.8 cubic m/s), which as I eyeball it on the USGS annual peakflow graph appears to be about a 2-year flood. This is actually consistent with my eyeballed estimate of the flow frequency produced by Sandy on Passage Creek, near Callan Bentley’s house in Virginia. I wonder whether that will be consistent for other rivers affected by Sandy.

For me, this was the first chance to the Cuyahoga River in action as it flows through Kent. The river sits in a gorge than separates the two halves of town, and that seems to keep the river from endangering much property in the town. But it did make for a pretty impressive roaring site and sound as I crossed the bridges today. Here are two pictures of Heritage Park in Kent on Friday afternoon about 4 pm. Contrast that with the low water pictures from early June.

Cuyahoga River in Kent Ohio with impressive whitewater as it passes through an old lock.

Cuyahoga River in Kent Ohio with impressive whitewater as it passes through an old lock. Photo at 4:15 pm November 2nd, 2012 by A. Jefferson.

Flooding downstream of an old dam

Note the water level relative to the trees and those vicious rapids downstream of the lock. The dam in the foreground has been taken off-line and turned into a Heritage Park. Photo by A. Jefferson 4:15 pm 2 November 2012.

Lock at low water

The same lock structure as above, except at low water levels. June 2012, photo by A. Jefferson. Note complete absence of rapids downstream of the lock.

Similar view looking downstream past the dam as the picture above. Note how much vegetation is above water here.

Happy New Water Year! For hydrologists, it’s already 2013.

Cross-posted at Highly Allochthonous

Trees with autumn colors on the banks of a river

The Upper Cuyahoga River as it might look about the time of the new water year. Photo by Ohio DNR (click image for source). A 40 km section upstream of Kent is a state scenic river and I really want to canoe it.

There’s nothing particularly deterministic about starting a new year on January 1st. Our wall calendars happen to do so because of the circumstances of history. For hydrologists in the northern hemisphere, January 1st is not a great time to declare one year dead and a new one born. So instead, we transition between years on the 1st day of October. October 1st, 2012 marks day 1 of the 2013 water year. But, why?

Many hydrologic analyses involve calculating statistics on an annual basis. We might want to calculate annual streamflow to determine how much drier 2012 was than 2011. Or we might want to look for trends in the size of floods. For the example of flood statistics, the most common way to get a time series of floods is to identify the largest flood occurring in each year. This “annual peak flow” record is then used within the framework of a probability distribution function to assign a probability of given size flood occurring in any one year. (Problematically, this has been called a “flood frequency distribution”, leading to unnecessary confusion on the part of the public, but I digress…)

We use only the largest flow each year to calculate statistics because it avoids statistical complication. Principally, we want to ensure all of our events are independent of each other. Let’s say there are two days with really high flows in a year. The highest flow is 27.8 m3/s and the second flow is 24.1 m3/s. If the first measurement was made on January 29th and the second one was from March 18th, then these two data are independent (i.e., not the same flood). But if one is from January 29th and the other is January 30th, they are clearly not independent and should not both be used to calculate statistics as if they were. So, we try to avoid this dependence issue by using only the largest flow each year.

Here’s where we come back to the idea of the water year. Let’s use an example from my local stream gage – the Cuyahoga River at Hiram Rapids. There was a big flood on December 31st, 1990 – the biggest flood of the whole year – reaching a peak flow of 71.4 m3/s. On January 1st, 1991 the water was still high – 66.8 m3/s. After that excitement, the rest of 1991 was pretty dry and flow never again gets anywhere near as high, peaking at 25.0 m3/s in early March. How do we calculate the statistics? If we used the calendar year as our basis, we’d end up double counting that late December flood and we’d throw our flood statistics off.

Instead, hydrologists use October 1st as our cut-off date. In many parts of the Northern Hemisphere, summer is a period of low streamflow, driven by strong evapotranspiration and atmospheric circulation patterns. (A prominent exception to the lack of summer flooding is when tropical cyclones make landfall.) In winter, rain-on-snow can produce large floods in some regions, while decreased evapotranspiration and more frontal storms increase the chances of flooding in some southern regions. In the spring, seasonal snowmelt produces flooding in northern and alpine regions. That leaves the autumn as the period least likely to have frequent flooding. Also, because evapotranspiration is subsiding with cooler temperatures, soil moisture and stream flow don’t tend to be recovering from their low points in the summer. So autumn is a time of transition and a time when extremes are unlikely. The graphs below illustrate this for my local stream gage, but similarly shaped distributions would likely exist for many other gages in the US and beyond.

Thus, it’s a perfect time of year to the clear the books and declare a new year for hydrologic statistics. And it’s got as much or more physical rationale than when we change the calendar on the wall. Happy New Water Year Everyone!

Bar graph showing months with the greatest frequency of flooding in December-April

USGS data on annual peak flows for the Cuyahoga River at Hiram Rapids (gage #04202000) illustrates that summer and fall have the least frequent big floods.

March has the highest discharge, July and August have the lowest.

Mean monthly discharge for the Cuyahoga River at Hiram Rapids shows that summer is the period of lowest flow and that by September and October average discharge is starting to increase.

New paper: Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Snowline near Skykomish, Washington (photo on Flickr by RoguePoet, used under Creative Commons)

Jefferson, A. 2011. Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions, Geophysical Research Letters, 38, L16402, doi:10.1029/2011GL048346.

Abstract:

In maritime mountainous regions, the phase of winter precipitation is elevation dependent, and in watersheds receiving both rain and snow, hydrologic impacts of climate change are less straightforward than in snowmelt-dominated systems. Here, 29 Pacific Northwest watersheds illustrate how distribution of seasonal snow, transient snow, and winter rain mediates sensitivity to 20th century warming. Watersheds with >50% of their area in the seasonal snow zone had significant (? ? 0.1) trends towards greater winter and lower summer discharge, while lower elevations had no consistent trends. In seasonal snow-dominated watersheds, runoff occurs 22–27 days earlier and minimum flows are 5–9% lower than in 1962, based on Sen’s slope over the period. Trends in peak streamflow depend on whether watershed area susceptible to rain-on-snow events is increasing or decreasing. Delineation of elevation-dependent snow zones identifies climate sensitivity of maritime mountainous watersheds and enables planning for water and ecosystem impacts of climate change.

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.

    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