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watershed hydrology

GSA 2013: Revisiting watershed drainage density: New considerations for hydrologic prediction

While I’ll be missing the festivities at the 125th anniversary edition of the the Geological Society of America, my able collaborator Sarah Lewis will be presenting our work in a session on “Quaternary Geology and Geomorphology: Past, Present, and Future.” Here’s what she’ll be showing off:

Revisiting watershed drainage density: New considerations for hydrologic prediction

S.L. Lewis, M. Safeeq, A.J. Jefferson, G.E. Grant

Watershed morphometry has long been identified as a major control on the shape and character of the hydrograph. Easily extractable landscape-level metrics have been explored for hydrologic prediction in ungaged watersheds, with varying success. In particular, mean drainage density (stream length/watershed area), which has a strong theoretical relationship to flow, has been both heralded and cast aside as an explanatory variable for hydrograph characteristics. However, previous approaches did not account for the spatial heterogeneity in drainage density within a single watershed. For example, many watersheds in the Oregon Cascades are comprised of both young lava flows with limited drainage networks, subtle peaks and sustained baseflows, and older highly dissected volcanics with steep slopes and flashy hydrographs. A mean drainage density fails to represent this dichotomy.

Here we revisit the long-standing conceptualization of drainage density as a good predictor of flow behavior at the landscape level. We depict drainage density (Dd) heterogeneity as a probability distribution function (pdf) of individual drainage densities within a watershed. Rather than limiting Dd to a single number (mean), we use standard quantitative descriptors of the pdf to explore landscape-level controls on flow regime. Two watersheds with similar mean values may have dramatically different pdfs and therefore exhibit variations in flow dynamics. We assert that some of the inconsistent results applying Dd as a predictive variable may be due to the accuracy with which a mean value can capture the behavior of a drainage network. In watersheds where drainage density is homogeneous, mean Dd may provide a good approximation of drainage behavior, but in watersheds where drainage density is heterogeneous, quantitative descriptors of the pdf can provide additional insight into flow dynamics.

Fantastic undergraduate research opportunity at Hubbard Brook Experimental Forest

Just the messenger about this great opportunity to get hydrology research experience at one of the pivotal locations for the development of hydrologic science working with fantastic colleagues:

Hillslope hydrology component of the Hubbard Brook REU:

We are seeking applicants for an REU position at the Hubbard Brook Experimental Forest in New Hampshire.  The program is a multidisciplinary project where students participate in a research project and also engage in outreach projects designed to help develop skills in communicating ecosystem information to broad audiences. The program runs from May 29 through August 7, 2013 and all students are expected to be in attendance on the start date. Students receive a $5000 stipend for the 10-week program, as well as free housing. Food costs are paid by the participants and run approximately $42/week. Students live at Hubbard Brook Research Foundation’s Pleasant View Farm adjacent to the Hubbard Brook Experimental Forest.

The overall objective of the hillslope hydrology project is to document varying flowpaths that water takes through soils in its journey through hillslopes on its way to streams. An REU student will work closely with a team with graduate students installing and operating tensiometers and pore water samplers, and collecting and characterizing soil samples. The approach of this project follows the emerging discipline of hydropedology, with implications for understanding water quality regulation and spatial patterns in forest habitats. (Mentors: Dr. Scott Bailey, US Forest Service and Dr. Kevin McGuire, Virginia Tech)

More information on the program and application information can found at The application deadline is February 8th.

New report: Challenges and Opportunities in the Hydrologic Sciences

The “blue book” has been updated and you can read and download a pre-publication PDF on the National Academies’ website for free. I’ve just been listening to a CUAHSI webinar summarizing the report, and I was please to see that a lot of the questions I’m interested in were highlighted by the committee that updated the report. For instance, there was specific mention of urban hydrology (and how changes to flowpaths and quantity alter water quality), the co-evolution of hydrology, landscapes, and life, and the need to understand the controls on the low flow extent of streams. I’ll be reading sections of this report in coming months, and if you want to get a sense of the state of hydrologic science, you would probably do well to start here too.

Watch Anne talk about channel initiation at AGU 2011

I gave two talks at the AGU meeting in San Francisco in December. One talk was in session “EP31G Predictive Understanding of Coupled Interactions Among Water, Life, and Landforms II”, and it was recorded and made available on Vimeo. While all the talks in the session were extremely interesting, if you want to skip to me, go to about 31 minutes and 30 seconds into the video.

EP31G : AGU Fall Meeting 2011 from American Geophysical Union on Vimeo.

AGU 2011 abstract: Controls on the hydrologic evolution of Quaternary volcanic landscapes

The following talk will be presented in the 2011 AGU fall meeting session on “EP41F. Posteruptive Processes Operating on Volcanic Landscapes I” on Thursday, December 8th from 9:15 to 9:30 am.

Controls on the hydrologic evolution of Quaternary volcanic landscapes
Anne J. Jefferson and Noemi d’Ozouville

1. Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC, United States.
2. UMR 7619 Sisyphe CNRS & UPMC, Universite Paris 6, Paris, France.

Conceptual models that explain the evolution of young volcanic landscapes require the prominent inclusion of processes which affect partitioning of water between surface and subsurface flows. Recently emplaced lava flows have no surface drainage, with infiltration to groundwater as the dominant hydrologic process. Older volcanic landscapes are often dominated by extensive drainage networks, fed by permanent or intermittent streams, which have deeply dissected the constructional topography. Drainage density, topography, and stream and groundwater discharge provide readily quantifiable measures of hydrologic and landscape evolution on volcanic chronosequences. We will use examples from the High Cascades, Galapagos, and elsewhere to illustrate the trajectories and timescales of hydrologic evolution.

We suggest that the surface-subsurface water partitioning is a function of volcanic architecture, climate-driven processes, and water-rock interactions. We will show that in mafic volcanic areas, climate-driven processes (such as weathering and dust deposition) control landscape evolution, while explosive eruptive products may be important for local hydrology. In the High Cascades, where precipitation exceeds 2 m/yr, landscape dissection has obliterated constructional morphology within 1 million years, while in the more arid Galapagos, million year old landscapes are largely undissected. Conversely, localized groundwater perching on pyroclastic layers or paleosols has been characterized in the Galapagos, but not in the Cascades, where pyroclastic activity is more limited in extent. In areas where explosive activity, including phreatomagmatism, dominates volcanism, the evolution of hydrology and topography occurs much more rapidly than in landscapes created by effusion. Hydrothermal circulation and water-rock interactions may play an important role in reducing deep permeability and altering subsurface flowpaths in some volcanic landscapes. Observed chronosequences can be complicated by juxtaposition of different age deposits, post-emplacement faulting, uplift or subsidence, and climate change, so detailed understanding of the landscape’s geologic history is a prerequisite for appropriate interpretation of hydrologic evolution in volcanic landscapes.

Lush vegetation in a pit crater on Santa Cruz Island

A "pit crater" in the highlands of Santa Cruz Island in the Galapagos shows preferential vegetation growth at the contact between lava flows, probably where water is more available. Photo by A. Jefferson.

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.


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.

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.

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.

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

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.

Graduate Assistantships: Biogeochemistry, Stream Ecology, and Hydrology at UNC Charlotte, NC

Come work with me!

Research assistantships are available at the MS or Ph.D. level at the University of North Carolina at Charlotte to participate in a recently funded NSF project investigating the effects of stormwater management on ecosystem function in urban watersheds.  The overall goal is to better understand and predict the impacts of stormwater BMPs on receiving streams over a range of spatial and temporal scales through a combination of field based research and watershed scale ecological modeling.  This interdisciplinary project will link (1) mass-balance based monitoring of individual BMPs, (2) ecosystem processes (nutrient uptake, metabolism, temperature and biological indices) in the receiving stream and (3) monitored and modeled watershed outputs of flow, nitrogen, and carbon.

Applicants interested in aquatic biogeochemistry, hydrology, stream ecology and/or watershed modeling are encouraged to apply.  Students will have flexibility to develop independent research questions within the context of this project that broadly address the interactions among hydrology, biogeochemistry and ecology in aquatic ecosystems.

Qualifications:  degree in biology, ecology, environmental engineering, hydrology or related field is required.  Successful applicants should have a strong interest in working in an interdisciplinary research environment, be creative, motivated and capable of working well both independently and cooperatively and possess strong communication and quantitative skills. Competitive stipends and tuition waivers are available for highly motivated students.  For more information on admission requirements and deadlines, visit  Additional information about the McMillan Lab can be found at  Opportunities exist for collaboration with the labs of Sandra Clinton and Anne Jefferson at UNC Charlotte who are collaborators on the project.

Interested students with strong motivation to succeed in research should contact Sara McMillan via email (  Please submit a statement of career goals and research interests, full CV, unofficial transcripts and GRE scores, and contact information for three potential references.  Review of applications will begin immediately and continue until suitable candidates are found. The anticipated start date is flexible, but should be sometime between January and August 2011.