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fluvial geomorphology

Southern Minnesota is geomorphologically exciting: Glacial outburst floods, knickpoint retreat, and terraces galore!

Today in my flvuial processes class, we’re going to discuss a great paper by Gran et al. on “Landscape evolution, valley excavation, and terrace development following abrupt postglacial baselevel fall.” The paper is set in a landscape I know well – southern Minnesota’s Minnesota River Basin. For my students in northeastern Ohio, this landscape would feel somewhat similar to the area around here, but not quite. Similarly, the glacial history has some degree of overlap (glaciers covering the region and retreating about ~14,000 years ago), but there are some unique elements of each place. Fortunately, I found a series of short video clips that do a nice job of setting the Minnesota River story in its context.

The tributaries to the Minnesota River are still relaxing after all of this geologic excitement. As a result, many of the tributaries exhibit knickpoints or knick zones – steepened areas on the channel profile.

Long profiles of the Le Sueur, Maple, and Big Cobb Rivers showing the presence of a major knick point around 30-35 kilometers upstream from the mouth of the river. Figure from Gran et al reproduced under a CC license, via SERC.

Long profiles of the Le Sueur, Maple, and Big Cobb Rivers showing the presence of a major knick point around 30-35 kilometers upstream from the mouth of the river. Figure from Gran et al reproduced under a CC license, via SERC.

You don’t have to go to the primary literature to learn about the knickpoints and what’s going on in the Minnesota tributaries, thanks to a nice short discussion by Karen Gran. There’s even a huge knickpoint left on the Mississippi River in Minneapolis as a result of the Glacial River Warren and draining of Lake Agassiz. You can read about that one here.

For a great discussion of fixed versus mobile knickpoints, check out this essay by Ben Crosby, who did his PhD work on a particularly knickpoint rich landscape in New Zealand. More good discussion of knickpoint mobility can be found in this blog post by Chuck Bailey. Finally, Steven Schimmrich has a nice series of blog posts on knickpoint retreat at Niagara Falls.

If that’s not enough, knickpoint retreat is often associated with the formation of terraces. There are two types of terraces to come to terms with. Cut-and-fill terraces, where the unconsolidated sediments are actually alluvium, show that the river has had periods of both aggradation and incision (and lateral planation of the valley bottom). In rivers with strath terraces, aggradational periods are either relatively minor or non-existent and the terraces represent alternating periods of incision and lateral planation. Callan Bentley has illustrated each type of terrace below, and you should see his post and comments for good discussion of the intricacies of naming and describing these features.

Terrace types, by Callan Bentley.

Terrace types, by Callan Bentley.

Development of hyporheic exchange and nutrient uptake following stream restoration

Next week, the Watershed Hydrology Lab will be well represented at the CUAHSI 2014 Biennial Colloquium. We’ll be presenting four posters, so here come the abstracts…

Development of hyporheic exchange and nutrient uptake following stream restoration

Stuart Baker and Anne Jefferson

Stream restoration is a multi-million dollar industry in Ohio, with major goals of improving water quality and degraded habitat. Yet restoration often falls short of significant improvements in water quality and biodiversity. It is thus important to improve the theory and practice of stream restoration in order to achieve greater benefits per dollar spent, yet there are limited data and understanding of the physical and biogeochemical responses to restoration that constrain the potential for water quality and ecological improvements. Hyporheic exchange, the flow of water into and out of the streambed, is an important stream process that serves critical roles in naturally functioning streams, allowing for stream water to participate with the substrate in various processes. Hyporheic flowpaths can be altered by the transport of fine sediment through the stream bed and are thus susceptible to changes in sediment regime and hydraulics, as well as the changes wrought by construction of a restoration project. The goal of this research is to determine the effectiveness of restoration in enhancing hyporheic flow and associated biogeochemical processes to improve water quality. Preliminary results from Kelsey Creek, OH, a second-order stream restored in August 2013, show a decrease in average hydraulic conductivity but an increase in heterogeneity from pre-restoration (geometric mean 8.47×10-5 m/s, range 1.18×10-6-1.19×10-3) to post-restoration (geometric mean 4.41×10-5 m/s, range 2.67×10-5-3.05×10-4) in piezometer nests through large constructed riffle structures. These piezometers also indicate dominance of downwelling throughout riffle structures with only isolated locations of upwelling. Transient storage and hyporheic exchange will be measured with resazurin injections for comparison between pre-restoration and post-restoration, and nutrient injections of NH4Cl at time points following the restoration will compare the nitrogen uptake rates of the restored reach to an unrestored reach downstream. Additional sites are planned for study to include restoration projects of different ages to examine the development of hyporheic exchange and biogeochemistry after completion of restoration projects.

After the dam comes out: groundwater-stream interactions and water quality impacts of former reservoir sites

Next week, the Watershed Hydrology Lab will be well represented at the CUAHSI 2014 Biennial Colloquium. We’ll be presenting four posters, so here come the abstracts…


After the dam comes out: groundwater-stream interactions and water quality impacts of former reservoir sites

Krista Brown and Anne Jefferson

Over that past decade, dam removals have become increasingly popular, as many dams near the end of their life expectancy. With an increasing number of anticipated dam removals coming in the near future this study aims to develop an understanding of groundwater-stream interactions and water quality in former reservoir sites after dam removals have occurred. Low head dams (~2 m) were removed in 2009 from Plum Creek in Kent, Portage County, Ohio and on Kelsey Creek in Cuyahoga Falls, Summit County, Ohio. Kelsey Creek reservoir has been unaltered since the dam removal and consists of a stream channel flowing through riparian- wetland environments, while Plum Creek reservoir underwent channel restoration in 2011. At Kelsey Creek, 20 piezometers and 3 wells were installed in the stream and riparian areas. Pressure transducers were also deployed in each well and stream from November 20, 2013 to January 5, 2014. Hydraulic conductivity was calculated using the Hvorslev method. Since October 2013, hydraulic heads have been recorded semi-weekly and water samples have been taken in the wells and stream. Water quality is being evaluated with field-measured pH, temperature, specific conductance, and dissolved oxygen, and ion chromatography of chloride, bromide, nitrate, sulfate and phosphate concentrations. Plum Creek is being used to understand the water quality effects of channel restoration at former reservoir sites.
At Kelsey Creek, hydraulic conductivity ranges five magnitudes, from 10?2 to 10?6 m/s, but wells near the channel, in an off-channel wetland, and on an adjacent hillslope respond similarly during high flow events. However, the well closest to the stream shows substantial variability in specific conductance, indicating bidirectional groundwater-stream exchange. Despite the wetlands and presumed greater groundwater-stream exchange in the unrestored Kelsey Creek, stream water quality is similar to the restored Plum Creek site. This suggests that the water quality measures considered here should not determine whether to restore channels within former reservoir sites. Findings from this research may be applicable when considering options for future dam removal sites.

Abstract: Evaluating restoration effects on transient storage and hyporheic exchange in urban and forested streams

A third abstract from our group for the 2012 Geological Society of America meeting:

EVALUATING RESTORATION EFFECTS ON TRANSIENT STORAGE AND HYPORHEIC EXCHANGE IN URBAN AND FORESTED STREAMS

OSYPIAN, Mackenzie L., Civil Engineering, University of North Carolina at Charlotte, Charlotte, NC 28262, mosypian@uncc.edu, JEFFERSON, Anne J., Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH 44240, and CLINTON, Sandra, Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223

Millions of dollars are spent each year on restoration projects designed to improve stream habitat, but few studies have investigated effects of restoration on hyporheic exchange and transient storage. Stream water-groundwater interactions and transient storage in four second-order streams (urban/forest; restored/urestored) were studied by measuring geomorphology, streambed vertical head gradients and water fluxes, and by using conservative, impulse-loaded tracer studies along with the OTIS model. The magnitude of upwelling and down welling was observed to be greatest in the restored urban stream, which contains large step structures, while the smallest gradients were observed in the unrestored urban stream, which is incised to bedrock. OTIS results show that the 120 m unrestored urban reach with a debris dam has an average transient storage of 1.8×10^-2 m2/m and an ? of 9.5×10^-4 s^-1 while a 55m restored forested reach with log sills has an average transient storage of 8.3×10^-2 m2/m and an ? of 1.5×10^-4 s^-1. Based on these results, we conclude that restoration changes transient storage metrics, and ongoing work aims to understand how these changes affect ecosystem health.

Spring Break: tracer injection in Beaver Dam Creek

Spring Break: tracer injection in Beaver Dam Creek

Spring Break: tracer injection in Beaver Dam Creek

Some of our students are in the field this week, injecting Cl- and Br- into a restored reach and an unrestored reach in tributaries of Beaver Dam Creek. Our goal is to understand the role of wood jams versus restoration structures in promoting stream-hyporheic exchange.

In the photo are Alea, Xueying, and Mackenzie. Photo by Brittany. They’ve got it so capably handled they didn’t even need Sandra or I out there with them today, but I’m going tomorrow for an excuse to be in the field as much as anything.

Spring Break: tracer injection in Beaver Dam Creek

Some of our students are in the field this week, injecting Cl- and Br- into a restored reach and an unrestored reach in tributaries of Beaver Dam Creek. Our goal is to understand the role of wood jams versus restoration structures in promoting stream-hyporheic exchange.

In the photo are Alea, Xueying, and Mackenzie. Photo by Brittany. They’ve got it so capably handled they didn’t even need Sandra or I out there with them today, but I’m going tomorrow for an excuse to be in the field as much as anything.

Spring Break: tracer injection in Beaver Dam Creek

Some of our students are in the field this week, injecting Cl- and Br- into a restored reach and an unrestored reach in tributaries of Beaver Dam Creek. Our goal is to understand the role of wood jams versus restoration structures in promoting stream-hyporheic exchange.

In the photo are Alea, Xueying, and Mackenzie. Photo by Brittany. They’ve got it so capably handled they didn’t even need Sandra or I out there with them today, but I’m going tomorrow for an excuse to be in the field as much as anything.

GSA 2011 abstract: Spatial variability in groundwater-stream interactions in first-order North Carolina Piedmont streams

At the 2011 GSA Meeting in Minneapolis next week, I’ll be presenting the following talk in the session “Monitoring and Understanding Our Landscape for the Long Term through Small Catchment Studies I: A Tribute to the Career of Owen P. Bricker.” My talk is in Minneapolis Convention Center: Room M100FG, on Wednesday, 12 October 2011 at 9:30 am.

Spatial variability in groundwater-stream interactions in first-order North Carolina Piedmont streams

JEFFERSON, Anne J. and MOORE, Cameron, Dept. of Geography and Earth Sciences, University of North Carolina at Charlotte,

Groundwater upwelling and hyporheic exchange are spatially variable in three first-order Piedmont streams, resulting in variable discharge, water chemistry and temperature. Stream gradient, valley confinement, and woody debris jams appear to be the major controls on the distribution and size of upwelling zones. Temperature and specific conductance values at 25 m intervals on 18 dates revealed distinct zones of groundwater-stream interaction, confirmed by discharge and piezometer measurements. Baseflow accumulates unevenly along the streams, with upper reaches in confined valleys generally gaining discharge more rapidly than lower reaches. Elevated calcium concentrations occur in groundwater upwelling zones, such as in a 50 m reach in which baseflow triples. Near their mouths, where the streams reach a river floodplain, baseflow quantity and chemistry may be influenced by a larger groundwater system. At a smaller scale, spatial variability in stream chemistry and streambed hydraulic gradients are dominantly controlled by the size and position of woody debris jams. Fine sediment wedges extend 5-15 m upstream of the 0.25-1 m high jams, and strong down-welling hydraulic gradients occur in these areas. Upwelling of water with higher specific conductance and moderated temperatures occurs downstream of the jams. Nitrate concentrations decreased up to 50% immediately below large woody debris jams, while ammonium concentrations tended to be highest there.

Rapid urbanization in the Carolina Piedmont is drastically altering headwater catchments, but well-documented reference watersheds are lacking. The measurements described above are from three first-order streams in forested watersheds, with permanent protection by a land conservancy. Their hydrology and water chemistry demonstrates the rich spatial variability of Piedmont headwater streams, and we hope that long-term study of these sites provides useful understanding for stream restoration and watershed management.

Debris jam and sediment in a first order Deep Creek at Redlair. Photo by Cameron Moore.

Debris jam and sediment in a first order Deep Creek at Redlair. Photo by Cameron Moore.

Simulating river processes…ooh shiny, stream table!

Cross-posted at Highly Allochthonous

I’ve got a shiny new Emriver Em2 river processes simulator (i.e., stream table), thanks to departmental equipment funds and enthusiastic colleagues. I’ve been on sabbatical this semester and away from campus, so I haven’t had a chance to play with it yet, but it is enticing me to return. I’ll be teaching Fluvial Processes fall semester, so I’m sure that my students and I will get plenty of chances to explore all of the nifty ways in which we can demonstrate and experiment with fluvial geomorphology. I’m also playing with ideas for using the Emriver model in my hydrogeology class in the spring. I think it will be a perfect way to demonstrate ideas of hyporheic flow, seepage erosion, and break through curves in tracer tests. I think my colleagues are planning to use it in sedimentology, geomorphology and hydrology classes, and one colleague may take it with him when he does outreach activities. I’m sure we will come up with even more uses for it once we get started.

Em4 model at work.

Em4 model at work in promoting discussion about whether the arrow points to a good place to build a house.


My appetite for experiment with the stream table was whetted by a recent visit to Carbondale, Illinois and the base of operations for Little River Research and Design (LRRD). Steve Gough is the owner of LRRD, the mastermind behind the Emriver models, and a genuinely fantastically nice person. Motivated by the idea that hands on education about stream processes is the best way to instill respect for and promote protection of streams and rivers, Steve has poured himself into making the best stream table on the market, and making it affordable enough to for people like me to get their hands on.

Steve Gough, Anne Jefferson and a research assistant in front of LRRD, May 2011

Steve Gough, Anne Jefferson and a research assistant in front of LRRD, May 2011

Personally, I’d always been somewhat underwhelmed by teaching- and demonstration-grade stream tables before seeing the Emriver ones. Partly it was because I’d seen and read about big research flumes, like those at the St. Anthony Falls Lab and Johns Hopkins. But another part of it was that every time I had a chance to play with a home-built stream table I was frustrated by what it couldn’t do. Principally, most stream tables don’t do a very good job of reproducing the meandering behavior of lowland streams. This has even been an area of active and high profile research in the fluvial geomorphology community. Steve’s use of low density plastic beads instead of quartz sand solves that problem pretty nicely, though there’s definitely still some braiding going on.

[youtube http://www.youtube.com/watch?v=ZBoeI3ZX7us&w=480&h=390]

In addition to the 2-m long Em2 model that I have, LRRD also makes an extremely cool and versatile 4-m long model Em4. With beads colored by size, you can see (and measure) the sorting and selective transport of sediments. You can tilt the table laterally – simulating differential uplift/subsidence across the basin. There’s even a groundwater feed and extraction system! This model is pretty much as cool as I can imagine – at least short of the big research flumes mentioned above.

I can personally attest that this stream table model has the versatility to entrance both a PhD and a preschooler for more than two hours…and the preschooler wanted to go back the next day! Below I’ve added some shots of the Em4 in action. What geomorphic processes do you see?

Em4 looking downstream

Looking dowstream, I see a transition from "bedrock" to alluvial substrate, a really nice train of standing waves, meandering, a floodwall, and some sort of infrastructure project in the floodplain gone horribly wrong.

base level fall

A sudden base level fall is driving incision through an old delta. The dark red sediment is the finest grain size.

tracer test

Green dye was used to examine hyporheic flow transversely through a mid-channel bar. Now blue dye is being added to look for zones of in-channel transient storage.

Ralph McGee and Cameron Moore will graduate next week!

Major congratulations to two Watershed Hydrogeology Lab graduate students who have finished writing their MS theses and will defend them next week. Ralph McGee and Cameron Moore both started in our MS in Earth Science program in August 2009, and less than two years later they have each completed impressive MS projects on headwater streams in Redlair Forest of the North Carolina Piedmont.

Ralph McGee will present his research on “Hydrogeomorphic processes influencing ephemeral streams in forested watersheds of the southeastern Piedmont U.S.A.” on Thursday, May 12th at 10:00 am in McEniry Hall, room 111 on the UNC Charlotte campus.

The unofficial title for Ralph’s work is “Tiny Torrents Tell Tall Tales.” Watch the video below to see why.
[youtube=http://www.youtube.com/watch?v=PjINxXuy5Aw&w=640&h=390]

Cameron Moore will present his research on “Surface/Groundwater Interactions and Sediment Characteristics of Headwater Streams in the Piedmont of North Carolina” on Friday, May 13th at 9:00 am in McEniry Hall, room 111 on the UNC Charlotte campus.

When Cameron started working on this project, I had thought that the story would focus on how fractured bedrock contributed to groundwater upwelling in the streams, but it turns out the small debris jams (like the one below) are the dominant driver of groundwater/stream interactions and spatial variability of channel morphology.

Debris jam in Deep Creek

Looking upstream at a debris jam in Deep Creek


Faculty, students, and the public are encouraged to attend the presentations and ask Ralph and Cameron any questions they may have.

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.