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hydrogeomorphology

AGU 2011 abstract: Understanding channel network extent in the North Carolina Piedmont in the context of legacy land use, flow generation processes, and landscape dissection

The following talk will be presented by Anne at the 2011 AGU fall meeting on Wednesday, December 7th from 9 to 9:15 am in the session “EP31G. Predictive Understanding of Coupled Interactions Among Water, Life, and Landforms II.” It will be in rooms 2022-2024, and the abstract acceptance said something about video on demand.

Understanding channel network extent in the North Carolina Piedmont in the context of legacy land use, flow generation processes, and landscape dissection

Anne J. Jefferson and Ralph W. McGee
Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, NC

Nearly all land in the eastern US Piedmont region was cleared for intensive agriculture following European settlement, but some areas have been afforested over the last century. In these areas, an extensive ephemeral stream network drains into perennial headwater streams. In order to understand the present-day functioning of the ephemeral network in afforested watersheds, we mapped 102 channel head positions at 6 sites and monitored 6 channels at 2 sites in North Carolina’s Piedmont. The ephemeral channels are activated by subsurface flow from high intensity precipitation with wet or dry soils, or long duration precipitation with wet soils. Overland flow does not occur upslope of channel heads in forested watersheds, but it is observed in present-day pastures and fields.

Channel head contributing areas range from 0.1 – 3.0 ha, with local slopes that average 0.13 (range: 0.04 – 0.36). The relationship between slope and area at the channel heads has the form c = AS1.1, with an exponent much lower than the commonly reported exponent of ~2 that is associated with subsurface or saturation overland flow. Instead, the lower exponent may reflect the legacy of 18th-19th century of intense land use and degraded cover, which may have produced turbulent overland flow upslope of channels. Though established by relict land use conditions, we suggest that this network extent is maintained by the frequent activation of the channels through subsurface flow under forest cover. Further, channel heads are located within or downslope of colluvial hollows suggesting that gullying from historical land use is not the most extensive channel network experienced by the Piedmont over the course its landscape evolution, and that the dissection of the landscape may be the result of a precipitation and land cover regime much different from the modern one.

Gully down to bedrock, Morrow Mountains State Park, North Carolina (photo by A. Jefferson)

Gully down to bedrock, Morrow Mountains State Park, North Carolina (photo by A. Jefferson)

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.

Is Anne a hydrologist? geomorphologist? hydrophillic geologist? or whathaveyou?

Cross-posted at Highly Allochthonous

The theme for the next edition of the geoblogosphere’s Accretionary Wedge carnival is along the lines of “what are you doing now?” Recently as I was whining to my Highly Allochthonous co-blogger about how busy my teaching was keeping me, and how I wouldn’t have time to write anything for the Wedge, Chris suggested that I exhume some navel-gazing writing I’d done a while ago and simply post that. And in slightly modified form, now I have.

So, what do I do? The major theme of my research is analyzing how geologic, topographic, and land use variability controls hydrologic response, climate sensitivity, and geomorphic evolution of watersheds, by partitioning water between surface and ground water. The goal of my research is to improve reach- to landscape-scale prediction of hydrologic and geomorphic response to human activities and climate change. My work includes contributions from field studies, stable isotope analyses, time series analyses, geographic information systems, and hydrological modeling. My process-based research projects allow me to investigate complex interactions between hydrology, geomorphology, geology, and biology that occur on real landscapes, to test conceptual models about catchment functioning, and to show whether predictive models are getting the right answers for the right reasons. My current and past research has allowed me to investigate landscapes as diverse as the Cascades Range volcanic arc, the Appalachian Mountains and Piedmont of the southeastern United States, the Canadian Arctic Archipelago, and the Upper Mississippi River watershed.

My on-going and developing research program focuses on three areas:

  1. Watershed influences on hydrologic response to climate variability and change;
  2. Controls on and effects of partitioning flowpaths between surface water and groundwater; and
  3. Influence of hydrologic regimes on landscape evolution and fluvial geomorphology

If you really want the long version of my research interests, venture onward. But don’t say I didn’t warn you.

Watershed influences on hydrologic response to climate variability and change

On-going climate change is predicted to have dramatic effects on the spatial distribution and timing of water resource availability. I use historical datasets, hydrologic modeling, and GIS analysis to examine how watershed characteristics can mediate hydrologic sensitivity to climate variability and change. Currently, I focus on climate sensitivity in watersheds with seasonal and transient snow and on down-scaling hydrologic impacts of climate change to smaller watersheds.

Watersheds with seasonal and transient snow: A long-held mantra is that watersheds with extensive groundwater are buffered from climate change effects, but in a pair of papers set in the Oregon Cascades, my collaborators and I showed the opposite to be true. Minimum streamflows in watersheds with abundant groundwater are more sensitive to loss of winter snowpack than in watersheds with little groundwater (Jefferson et al., 2008, Tague et al., 2008). Glaciers are another water reservoir often thought to buffer climate change impacts, and in a paper in review, we show that projected glacier loss from Mt. Hood will have significant impacts on water resources in the agricultural region downstream.

I have also been examining hydroclimate trends relative to hypsometry (elevation distribution) of watersheds in the maritime Pacific Northwest. Almost all work investigating hydrologic effects of climate change in the mountainous western United States focuses on areas with seasonal snowpacks, but in the maritime Northwest, most watersheds receive a mixture of winter rain and snow. My research investigates how much high-elevation watershed area is necessary for historical climate warming to be statistically detectable in streamflow records. Preliminary results were presented at the American Geophysical Union meeting in 2008, and I’m working on a paper with more complete results. Extending this work into the modeling domain, I am currently advising a graduate student using SnowModel to investigate the sensitivity of snowmelt production to projected warming in the Oregon Cascades, Colorado’s Fraser Experimental Forest, and Alaska’s North Slope, in collaboration with Glen Liston (Colorado State University).

Down-scaling climate impacts to watersheds and headwater streams: Most studies of hydrologic impacts of climate change have focused on regional scale projections or large watersheds. Relatively little work has been done to understand how hydrologic and geomorphic impacts will be felt in mesoscale catchments or headwater stream systems, yet most of the channel network (and aquatic habitat) exists in these small streams. In August 2009, I submitted a proposal to a Department of Energy early career program to investigate the effect of climate change on hydrology of the eastern seaboard of the US. This work proposed to contrast North Carolina’s South Fork Catawba River and New Hampshire’s Pemigewassett River and their headwater tributaries through a combination of modeling and field observations of the sensitivity of headwater stream networks to hydroclimatic variability. While the project was not funded, I am using the reviews to strengthen the proposal, and I plan to submit a revised proposal to NSF’s CAREER program in July. I have a graduate student already working on calibrating the RHESSys hydroecological model for the South Fork of the Catawba River.

Controls on flowpath partitioning between surface water and groundwater and the effects on stream hydrology, geomorphology and water quality

Many watershed models used in research and management applications make simplifying assumptions that partition water based on soil type and homogeneous porous bedrock. These assumptions are not reflective of reality in many parts of the world, including the fractured rocks of North Carolina’s Piedmont and Blue Ridge provinces. I am interested in understanding how water is partitioned between groundwater and surface water in heterogeneous environments, and what effect this partitioning has on stream hydrology, geomorphology, and water quality. My interest in the controls on flowpath partitioning began during my work in the Oregon Cascades Range, where I showed that lava flow geometry controlled groundwater flowpaths and the expression of springs (Jefferson et al., 2006). Currently, I am using fractured rock environments and urbanizing areas as places to explore the effects of heterogeneous permeability.

Fractured rock: The Piedmont and Blue Ridge provinces of the eastern United States are underlain by crystalline rocks, where groundwater is largely limited to discrete fractures. Groundwater-surface water interactions on fractured bedrock are largely unexplored, particularly at the scale of small headwater streams. I am interested in how groundwater upwelling from bedrock fractures and hyporheic flow influence the hydrology and water quality of headwater streams. A small grant facilitated data collection in three headwater streams which is forming the thesis for one of my graduate students, has precipitated a collaborative project with hydrogeologists from the North Carolina Division of Water Quality, and will serve as preliminary data for a proposal to NSF Hydrologic Sciences in June 2010.

Urban watersheds: Urbanization alters the partitioning of flowpaths between surface water and groundwater, by creating impervious surfaces that block recharge and installing leaky water and sewer lines that import water from beyond watershed boundaries. Also, the nature of the drainage network is transformed by the addition of stormwater sewers and detention basins. In September 2009, my collaborators and I submitted a proposal to NSF Environmental Engineering to look at how stormwater best management practices (BMPs) mitigate the effects of urbanization on headwater stream ecosystem services. While we weren’t funded, we were strongly encouraged to resubmit and did so in March 2010. We are also submitting a proposal to the National Center for Earth Surface Dynamics (NCED) visitor program to use the Outdoor Stream Lab at the University of Minnesota to investigate the interplay between stormwater releases and in-stream structures.

Influence of hydrologic regimes on landscape evolution and fluvial geomorphology

The movement of water on and through the landscape results in weathering, erosion, transport, and deposition of sediment. In turn, that sediment constrains the future routing of water. I am interested in how the hydrologic regime of a watershed affects the evolution of topography and fluvial geomorphology. My work in this area has examined million-year scales of landscape evolution in high permeability terrains, century-scale evolution of regulated rivers, and the form and function of headwater channels.

Evolution of high permeability terrains: The youngest portions of Oregon’s High Cascades have almost no surface water, because all water infiltrates into high permeability lava flows. Yet on older parts of the landscape, streams are abundant and have effectively eroded through the volcanic topography. In a paper in Earth Surface Processes and Landforms (Jefferson et al., 2010), I showed that this landscape evolution was accompanied and facilitated by a hydrologic evolution from geomorphically-ineffective stable, groundwater-fed hydrographs to flashy, runoff-dominated hydrographs. This coevolutionary sequence suggests that permeability may be an important control on the geomorphic character of a watershed.

Human and hydrologic influences on large river channels: Almost all large rivers in the developed world are profoundly affected by dams, which can alter the hydrologic regime by suppressing floods, supplementing low flows, and raising water levels in reservoirs. On the Upper Mississippi River, in the 70 years since dam construction, some parts of the river have lost islands, and with them habitat diversity, while in other areas new islands are emerging. In 2008-2009, I had a small grant that facilitated the examination of some islands with a unique, unpublished long-term topography dataset and its correlation with hydrologic patterns and human activities. This project became the thesis research of one of my graduate students, who will be defending his M.S. in May 2010.

Headwater channel form and function: Although headwater streams constitute 50-70% of stream length, the geomorphic processes that control their form and function are poorly understood. Most recent research on geomorphology of headwater streams has focused on streams in very steep landscapes, where debris flows and other mass wasting processes can have significant effects on channel geometry. In the Carolina Piedmont, gentle relief allows me to investigate the formation and function headwater channel networks, isolated from mass wasting processes. One of my graduate students has collected an extensive sediment size distribution dataset which shows that, at watershed areas <3 km2, downstream coarsening of sediment is more prevalent than the downstream fining widely observed in larger channels. Another graduate student is collecting data on channel head locations and flow recurrence and sediment transport in ephemeral channels in order to sort out the relative influences of topography, geology, and legacy land use effects on the uppermost reaches of headwater streams. Both of these projects have already resulted in presentations at GSA meetings.

Whew. So that’s what I do, between teaching some field-intensive courses and raising a preschooler. But, what am I? Hydrologist? Geomorphologist? Hydrophillic geologist? Or something else entirely?

GSA Abstract: Hydrogeomorphic controls on the expression of stream water in less than 1 km2 Piedmont watersheds

The Watershed Hydrogeology lab abstract for the Northeastern/Southeastern Geological Society of America Meeting in Baltimore, March 14-16, 2010. I’ll be giving a talk at 8:45 am on Monday, March 15th in session T24. Hydrogeology of Wetlands and Watershed Processes. It’s also looking like all of the other co-authors will be attending the meeting as well, so if you come you can hear the inside scoop from the students doing the work.

Hydrogeomorphic controls on the expression of stream water in less than 1 km2 Piedmont watersheds

Jefferson, McGee, Moore, and Caveny-Cox
UNC Charlotte, Dept. of Geography and Earth Sciences

Rapid development of the North Carolina Piedmont is converting headwater watersheds from forested or agricultural to urbanized landscapes, affecting the hydrology and geomorphology of small streams. We examine the water sources and contributing areas to headwater streams in 12 small, forested watersheds near the Charlotte metropolitan area. These watersheds have experienced a history of timber harvest and agriculture typical of Piedmont landscapes. Stream networks are characterized by regolith-bedded ephemeral channels that contribute to mixed bedrock and gravel-bed perennial channels. Source areas for ephemeral channels are on the order of 1 ha, while perennial flow heads have contributing areas on the order of 10 ha. Surface flow in ephemeral reaches occurs during rain events exceeding 2.5 cm and ceases within hours of rainfall. Between rain events, channel head locations vary by 0-14 m and correspond to bedrock exposures or soil pipes. Streams show varying patterns of baseflow discharge versus watershed area, with some streams showing evidence of concentrated zones of groundwater upwelling. Upwelling zones, characterized by temperature and conductance perturbations, are found in both bedrock and alluvial reaches and are stationary across seasons. Down-welling is observed in sediment wedges upstream of fallen logs or debris jams, sometimes leading to complete dewatering of surface baseflow. There are no consistent longitudinal trends in sediment size, and there is partial mobility of bed sediments under moderately-frequent flows. While the study watersheds represent pre-urbanization hydrogeomorphology, legacy land-use effects may contribute to variations in channel network extent and incision in the study watersheds.