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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.

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

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.