Currently browsing tag

hydrographs

Green infrastructure research featured on Kent Wired

Kent Wired, the electronic version of Kent State University’s student media, ran a story on Saturday about the work Kimm Jarden and I have been doing on the effectiveness of green infrastructure retrofits in a neighborhood in Parma, Ohio.  Hopefully I’ll have more to say about this in the next few days. In the meantime, if you want a glimpse of what we’ve been up to, you can check out the news article here.

Stormwater control measures modify event-based stream temperature dynamics in urbanized headwaters

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…

Stormwater control measures modify event-based stream temperature dynamics in urbanized headwaters

Grace Garner1, Anne Jefferson2*, Sara McMillan3, Colin Bell4 and David M. Hannah1
1School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.
2Department of Geology, Kent State University, Kent, OH, 44240, USA
3Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA
4Department of Infrastructure and Environmental System, University of North Carolina at Charlotte, Charlotte, NC, 28223, USA

Urbanization is a widespread and growing cause of hydrological changes and ecological impairment in headwater streams. Stream temperature is an important control on physical, chemical and ecological processes, and is an often neglected water quality variable, such that the effects of urban land use and stormwater management on stream temperature are poorly constrained. Our work aims to identify the influence of stormwater control measures (SCMs) of differing design and location within the watershed on the event-based temperature response of urban streams to precipitation in the North Carolina Piedmont, in order to improve prediction and management of urban impacts. Stream temperature was measured within SCMs, and upstream and downstream of them in two streams between June and September 2012 and 2013. Approximately 60 precipitation events occurred during that period. To unambiguously identify temperature increases resulting from precipitation, surges were identified as a rise in water temperature of ?0.2°C between the hours of 15:30 and 5:30, when the diurnal temperature cycle is either decreasing or static on days without precipitation. Surges up to 5°C were identified in response to precipitation events, with surges occurring both upstream and downstream of the SCM under some conditions. Surges were also recorded within the SCMs, confirming that temperature surges are the result of heated urban runoff. Classification tree modeling was used to evaluate the influence of hydrometeorological drivers on the generation and magnitude of temperature surges. In both streams, event precipitation, antecedent precipitation, and air temperature range were identified as the drivers of whether or not a surge was observed and how large the surge was, though the order and thresholds of these variables differed between the two sites. In a stream with an off-line, pond SCM, the presence of the pond in the lower 10% of the watershed did not affect the magnitude of temperature surges within the stream, but the pond itself had a wider range of surge magnitudes than did the stream. In a watershed with a large in-line pond, and a downstream contributing wetland SCM receiving flow from 40% of the watershed, the wetland increased both the frequency and magnitude of temperature surges observed in the stream. Our results suggest dynamic hydrometeorological conditions, SCM design, and position within a watershed all influence whether stormwater management reduces or enhances temperature surges observed within urban headwater streams, and that these factors should be considered in the recommendations for urban stormwater management systems.

Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

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…

Assessing impacts of green infrastructure at the watershed scale for suburban streets in Parma, Ohio

Kimberly Jarden, Anne Jefferson, Jennifer Grieser, and Derek Schaefer

High levels of impervious surfaces in urban environments can lead to greater levels of runoff from storm events and overwhelm storm sewer systems. Disconnecting impervious surfaces from storm water systems and redirecting the flow to decentralized green infrastructure treatments can help lessen the detrimental effects on watersheds. The West Creek Watershed is a 36 km2 subwatershed of the Cuyahoga River that contains ~35% impervious surface. We seek to evaluate the hydrologic impacts and pollution reduction of street scale investments using green infrastructure best management practices (BMPs), such as rain gardens, bioretention, and rain barrels. Before-after-control-impact design will pair two streets with 0.001-0.002 ha. lots and two streets with 0.005-0.0075 ha. lots. Flow meters have been installed to measure total discharge, velocity, and stage pre– and post-construction. Runoff data has been preliminarily analyzed to determine if peak discharge for large (> 10 mm) and small (<10 mm) storm events has been reduced after installation of BMPs on the street with 0.001-0.002 ha. lots. Initial results show that the peak flows have not been reduced for most storm events on the street with the green infrastructure. However, several larger events show that peak flows have been reduced on the treatment street and need to be further investigated to ensure no outside hydrological impacts are having an effect on the flow. Initial analysis of total flow volume for each event, pre- and post-construction, show that total volume has increased on the street with green infrastructure treatments. Possible explanation for the increase on flow volume could be attributed to under drains from bioretention creating a more connected flow path to the storm drain or an upstream leak in the control street storm drain. Each scenario will be investigated further to confirm results. Further research will include analysis of the total effect of street-scale BMPs on storm hydrograph characteristics including, hydrograph regression behavior and lag time. Analysis on the accumulation of metals in the bioswales and the reduction of metals in street runoff will also be conducted to determine if the BMP treatments are capturing pollutants associated with storm water. After studying the effect of each individual treatment, we will define the level of disconnected impervious surfaces needed in order to achieve a natural hydrologic regime in this watershed.

Abstract: Timescales of drainage network evolution are driven by coupled changes in landscape properties and hydrologic response

I will be at the CUAHSI 3rd Biennial Colloquium on Hydrologic Science and Engineering on July 16-18, 2012 in Boulder, Colorado. I’ve been asked to speak in a session on the co-evolution of geomorphology and hydrology. This is a cool opportunity for me, as I’ve been thinking about co-evolution in both volcanic landscapes and Piedmont gullies for the past couple of years. I’m going to attempt to stitch those two very different landscapes and timescales together in one conceptual framework in the talk, and I guess we’ll see how it goes.

Timescales of drainage network evolution are driven by coupled changes in landscape properties and hydrologic response
Anne J. Jefferson

In diverse landscapes, channel initiation locations move up or downslope over time in response to changes in land surface properties (vegetation, soils, and topography) which control the partitioning of water between subsurface, overland, and channelized flowpaths. In turn, channelized flow exerts greater erosive power than overland or subsurface flows, and can much more efficiently denude and dissect the landscape, leading to altered flowpaths and land surface properties. These feedbacks can be considered a fundamental aspect of catchment coevolution, with the headward extent of the stream network and landscape dissection as prime indicators of the evolutionary status of a landscape.

Photo by Ralph McGee, used with Permission.

Gullying in a Piedmont forest, downslope from a pasture. Cabin Creek headwaters, Redlair. Photo by Ralph McGee, used with permission.

Drainage network evolution in response to landscape change may occur over multiple timescales, depending on the rapidity of change in the hydrogeomorphic drivers. Climate and lithology may also modify the rates at which drainage networks respond to change in land surface properties. On basaltic landscapes, such as the Oregon Cascades, timescales of a million years or more can be necessary to evolve from an undissected landscape with slow, deep groundwater drainage to a fully-dissected landscape dominated by shallow subsurface stormflow and rapid hydrograph response in streams. This evolution seems to be driven by a slow change in land surface properties and permeability as a result of weathering, soil development, and mantling by low permeability materials, but may also reflect the high erosion resistance of crystalline bedrock. Conversely, rapid or near-instantaneous changes in land surface properties , such as accompanied the beginning of intensive agriculture in the southeastern Piedmont, can propagate into rapid (1-10 year) changes in channel network extent on clay-rich soils. Where agriculture has been abandoned in this region and forests have regrown, downslope retreat and infilling of extensive gully networks is occurring on decadal timescales.

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.

New publication: Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA

ResearchBlogging.org

How does a landscape go from looking like this…

<2000 year old landscape on basaltic lava with no surface drainage

~1500 year old basaltic lava landscape with no surface drainage

to looking like this?

2 Million year old landscape on basaltic lava

2 Million year old landscape on basaltic lava. Note steep slopes and incised valleys

Find out in my new paper in Earth Surface Processes and Landforms.

Hint: Using a chronosequence of watersheds in the Oregon Cascades, we argue that the rates and processes of landscape evolution are driven by whether the water sinks into the lava flows and moves slowly toward springs with steady hydrographs or whether the water moves quickly through the shallow subsurface and creates streams with flashy hydrographs. Further, we suggest that this water routing is controlled by an elusive landscape-scale permeability which decreases over time as processes like chemical weathering create soil and clog up pores in the rock. And as a bonus, because of the high initial permeability of basaltic landscapes, the formation of stream networks and the dissection of the landscape appears to take far longer than in places with less permeable lithologies.

Jefferson, A., Grant, G., Lewis, S., & Lancaster, S. (2010). Coevolution of hydrology and topography on a basalt landscape in the Oregon Cascade Range, USA Earth Surface Processes and Landforms, 35 (7), 803-816 DOI: 10.1002/esp.1976

The hydrogeology of Yellowstone: It's all about the cold water

Cross posted at Highly Allochthonous

ResearchBlogging.orgThe Yellowstone caldera is home to thousands of geothermal springs and 75% of the world’s geysers, with kilometers-deep groundwater flow systems that tap magmatic heat sources. As that hot groundwater rises toward the surface, it interacts with shallower, cooler groundwater to produce multi-phase mixing, boiling, and a huge array of different hydrothermal features. While the deep, geothermal water is sexy and merits both the tourist and scientific attention given to it, there’s a largely untold story in the shallow groundwater, where huge volumes of cold water may advect more heat than the hydrothermal features.

Grand Prismatic Spring at Yellowstone National Park. Photo by Alaskan Dude on Flickr.
Grand Prismatic Spring. (Photo by Alaskan Dude on Flickr.)

Yellowstone is a rhyolitic caldera that has produced 6000 cubic kilometers of ash flow tuffs, rhyolites, and basalts that form a poorly-characterized, heterogeneous fractured rock aquifer, hosting both hot/deep and cold/shallow flow systems. The Yellowstone volcanics lie on top of the Rocky Mountain Cordillera, which itself is a complex hydrogeologic system, ranging from low permeability metamorphic rocks to high permeability limestones.

In a paper in the Journal of Hydrology, Gardner and colleagues (2010) use stream hydrographs and groundwater residence times to characterize the cold, shallow groundwater of the greater Yellowstone area. Stream hydrographs, or the time series of stream discharge, are useful indicators of groundwater dynamics, because in between rain or snowmelt events, streamwater is outflowing groundwater. The recession behavior of a hydrograph during periods between storms can be used to estimate aquifer volumes. In the Yellowstone region, the annual hydrograph is strongly dominated by the snowmelt peak, and Gardner et al. used the mean daily discharge record from 39 streams to characterize the recession behavior of streams on different lithologies. What they found was that streams flowing in watersheds dominated by volcanic rocks have much less variable hydrographs than those on other rock types. The figure below uses data from the USGS to illustrate these differences, which are in line with studies in the Oregon Cascades* and elsewhere which suggest that young volcanic rocks produce groundwater-fed streams with muted hydrographs.

yellowstone-hydrograph.jpg
Daily discharge for the Firehole River (USGS gage #06036905) and Soda Butte Creek (USGS gage #06187950) for the 2006-2007 water years, expressed on a unit area basis.

Using a nifty technique to separate the recessions into components attributable to snowmelt versus groundwater, Gardner et al. were able to calculate a ratio of the groundwater discharge to the total discharge of each stream and to calculate the hydraulic diffusivity, which is a ratio of permeability (how easily a fluid moves through a rock) compared to the amount of water stored in the system. If hydraulic diffusivity is low, the flow in the stream decreases slowly over time, like the Firestone River in the figure above. But hydraulic diffusivity can be low either because of low permeability or large aquifer storage volumes, so being able to tease apart those two components is key to understanding the hydrograph behavior. Gardner et al. did this by looking at the ratio of groundwater discharge to maximum discharge and using that as an index of aquifer storage. Based on these ratios, Gardner et al. separated the streams in the Yellowstone area into three groups (runoff-dominated, intermediate, and groundwater-dominated) with contrasting hydrogeologic properties.

Upper Cenozoic Geologic Map, Yellowstone Plateau
Geologic map of a portion of the Yellowstone Plateau, with approximate locations of stream gages of interest noted. Modified from Christiansen (2001, USGS Prof. Pap. 729-G).

Soda Butte and Teton Creeks are runoff dominated, with low groundwater storage and middling recession behavior. Since there is little groundwater storage, in order for hydraulic diffusivity to be low, then permeability must also be low. Sure enough, Teton Creek lies on top of Precambrian gneiss and granite, and unfractured metamorphic and intrusive igneous rocks like these have the lowest possible permeabilities. The Soda Butte Creek watershed comprises Eocene Absaroka volcanics, and older volcanic rocks like these can be quite weathered to clays and relatively impermeable.

The intermediate watersheds of Tower Creek and Cache Creek have significant ratios of groundwater discharge to maximum discharge, but their hydrographs recede rapidly over the summer. This means that they have high permeabilities relative to their aquifer storage volume. The Tower Creek watershed has Eocene tuffs and glacial valleys with alluvial fill, and Cache Creek watershed has Paleozoic carbonates. These materials are known for their high permeabilities, and the low storage volumes can be explained if those layers thinly overly less conductive materials.

The Firehole River, Gibbon River, and Snake River above Jackson Lake are groundwater-dominated, with very high permeabilities but even larger aquifer storage volumes. All of those streams drain primarily Quaternary Yellowstone volcanics, and this hydrologic behavior is in keeping with other young volcanic terrains.

Not content to stop with this hydrogeologic classification of the Yellowstone area, Gardner et al. collected water samples from small, cold springs to analyze CFC and tritium concentrations, which are useful tracers of groundwater travel times. For the springs they sampled, they found an average travel time (from recharge to discharge) of ~30 years. Using those CFC-derived groundwater transit times and some back-of-the-envelope estimates of aquifer geometry, Gardner et al. estimate that the Quaternary Yellowstone volcanics have a permeability of 10-11 to 10-13 m2, which is in line with estimates of young volcanics elsewhere. They also estimated that the aquifer depth represented by these small springs was ~70 m, but speculated that deeper flowpaths might have been discharging directly into the streams, out of reach of their CFC and tritium sampling abilities.

Finally, Gardner et al. note that the cold springs they studied are actually not as cold as they should be. In fact, they appear to be what are coming to be called “slightly thermal” springs. Groundwater recharge temperature is commonly assumed to be approximately mean annual temperature, and in the Norris Geyser Basin area, that’s around 4-5 &deg C. But the cold springs in the area are around 10 &deg C. Using this temperature difference and a handy equation from Manga and Kirchner (2004), Gardner et al. are able to calculate the heat flux advected by these cool springs. Their value of ~3800 W/m2 for the springs around Norris is about 10% of the heat flux from the Norris and Gibbon Geyser Basins themselves. That number becomes even more astonishing when you consider the relative scales of the cool versus the thermal groundwater systems. Geyser basins cover ~10 km2 of the Yellowstone Plateau, whereas cool groundwater drains under the entire ~1000 km2 plateau, and could be discharging far more heat than those showy thermal springs and geysers themselves.

So if you happen to go to Yellowstone this summer, in between gawking at Old Faithful, Artist Paint Pots, and Mammoth Hot Springs, take a few moments to appreciate the waters of the less dramatic cool rivers and streams. Their waters too are profoundly shaped by the geologic history of Yellowstone, and they are taking an awful lot of heat.

*Disclaimer: My PhD research focused on the hydrology and hydrogeology of volcanic aquifers and streams of the Oregon Cascades.

Payton Gardner, W., Susong, D., Kip Solomon, D., & Heasler, H. (2010). Snowmelt hydrograph interpretation: Revealing watershed scale hydrologic characteristics of the Yellowstone volcanic plateau Journal of Hydrology, 383 (3-4), 209-222 DOI: 10.1016/j.jhydrol.2009.12.037

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?

My picks of the November literature

It is not that there was no October literature to pick. My time to read articles simply disappeared in the lead-up to and excitement of the Geological Society of America meeting. This month, however, I am back on track and I will try to update this post as I move through the last few weeks of November.

Fussel, H-M. 2009. An updated assessment of the risks from climate change based on research published since the IPCC Fourth Assessment Report. Climatic Change (2009) 97:469–482. doi:10.1007/s10584-009-9648-5
The takeaway message is this: While some topics are still under debate (e.g., changes to tropical cyclones), most recent research indicates that things are looking even worse now than we thought a few years ago. Greenhouse gas emissions are rising faster than we anticipated, and we have already committed to substantial warming, which is currently somewhat masked by high aerosol concentrations. It is increasingly urgent to find mitigation and adaptation strategies. Not good.

Gardner, LR. 2009. Assessing the effect of climate change on mean annual runoff. Journal of Hydrology. 379 (3-4): 351-359. doi:10.1016/j.jhydrol.2009.10.021
This fascinating article starts by showing a strong correlation (r2 = 0.94) between mean annual runoff and a function of potential evapotranspiration and precipitation. The author then goes on to derive an equation that shows how temperature increases can be used to calculate the change in evapotranspiration, therefore solving the water budget and allowing the calculation of the change in mean annual runoff. Conversely, the same equation can be used to solve for the necessary increase in precipitation to sustain current runoff under different warming scenarios.

Schuler, T. V., and U. H. Fischer. 2009.Modeling the diurnal variation of tracer transit velocity through a subglacial channel, J. Geophys. Res., 114, F04017, doi:10.1029/2008JF001238.
The authors made multiple dye tracer injections into a glacial moulin and then measured discharge and tracer breakthrough at the proglacial channel. They found strong hysteresis in the relationship between tracer velocity and proglacial discharge and attributed this hysteresis to the adjustment of the size of a subglacial Röthlisberger channel to hydraulic conditions that change over the course of the day. Cool!

Bense, V. F., G. Ferguson, and H. Kooi (2009), Evolution of shallow groundwater flow systems in areas of degrading permafrost, Geophys. Res. Lett., 36, L22401, doi:10.1029/2009GL039225.
Warming temperatures in the Arctic and sub-arctic are lowering the permafrost table and activating shallow groundwater systems, causing increasing baseflow discharge of Arctic rivers. This paper shows how the groundwater flow conditions adjust to lowering permafrost over decades to centuries and suggests that even if air temperatures are stabilized, baseflow discharge will continue to increase for a long time.

Soulsby, Tetzlaff, and Hrachowitz. Tracers and transit times: Windows for viewing catchment scale storage. Hydrological Processes. 23(24): 3503 – 3507. doi: 10.1002/hyp.7501
In this installment of Hydrological Processes series of excellent invited commentaries, Soulsby and colleagues remind readers that although flux measurements have been the major focus of hydrologic science for decades, it is storage that is most relevant for applied water resources problems. They show that tracer-derived estimates of mean transit time combined with streamflow measurements can be used to calculate the amount of water stored in the watershed. They use their long-term study watersheds in the Scottish Highlands to illustrate how transit time and storage scale together and correlate with climate, physiography, and soils in the watersheds. Finally, they argue that while such tracer-derived storage estimates have uncertainties and are not a panacea, they do show promise across a range of scales and geographies.

Chatanantavet, P., and G. Parker (2009), Physically based modeling of bedrock incision by abrasion, plucking, and macroabrasion, J. Geophys. Res., 114, F04018, doi:10.1029/2008JF001044.
Over the past 2 decades, geomorphologists have developed much better insight into the landscape evolution of mountainous areas by developing computerized landscape evolution models. A key component of such models is the stream power rule for bedrock incision, but some have complained that is not physically based enough to describe. In this paper, the authors lay out a new model for bedrock incision based on the mechanisms of abrasion, plucking, and macroabrasion (fracturing and removal of rock by the impact of moving sediment) and incorporating the hydrology and hydraulics of mountain rivers. This could be an influential paper.

Payn, R. A., M. N. Gooseff, B. L. McGlynn, K. E. Bencala, and S. M. Wondzell (2009), Channel water balance and exchange with subsurface flow along a mountain headwater stream in Montana, United States, Water Resour. Res., 45, W11427, doi:10.1029/2008WR007644.

Tracer tests were conducted along 13 continuous reaches of a mountain stream to quantify gross change in discharge versus net loss and net gain. Interestingly, the change in discharge over some reaches did not correspond to calculations of net loss or net gain based on tracer recovery. These results suggests that commonly used methods for estimating exchange with subsurface flow may not be representing all fluxes. Bidirectional exchange with the subsurface, like that found in this paper, is likely to be very important for nutrient processing and benthic ecology.

Please note that I can’t read the full article of AGU publications (including WRR, JGR, and GRL) until July 2010 or the print issue arrives in my institution’s library. Summaries of those articles are based on the abstract only.

People just keep publishing interesting stuff.

Fiorillo, F. 2009. Spring hydrographs as indicators of droughts in a karst environment. Journal of Hydrology 373: 290-301.

Rosenberry, D.O. and J. Pitlick. 2009. Effects of sediment transport and seepage direction on hydraulic properties at the sediment–water interface of hyporheic settings. Journal of Hydrology 373: 377-391.

Gresswell, R. et al. 2009. The design and application of an inexpensive pressure monitoring system for shallow water level measurement, tensiometry and piezometry. Journal of Hydrology 373: 416-425.

Fryar, A.E. 2009. Springs and the Origin of Bourbon [Historical Note], Ground Water, 47(4): 605-610.

Cardenas, M. Bayani. 2009. Stream-aquifer interactions and hyporheic exchange in gaining and losing sinuous streams Water Resour. Res., Vol. 45, No. 6, W06429

Selker, John; Ferre, Ty P. A. 2009. The ah ha moment of measurement: Introduction to the special section on Hydrologic Measurement Methods Water Resour. Res., Vol. 45, No. null, W00D00

Hodgkins, Glenn A. 2009. Streamflow changes in Alaska between the cool phase (1947-1976) and the warm phase (1977-2006) of the Pacific Decadal Oscillation: The influence of glaciers Water Resour. Res., Vol. 45, No. 6, W06502

Matott, L. Shawn; Babendreier, Justin E.; Purucker, S. Thomas Evaluating uncertainty in integrated environmental models: A review of concepts and tools Water Resour. Res., Vol. 45, No. 6, W06421

Orr, Cailin H.; Clark, Jeffery J.; Wilcock, Peter R.; Finlay, Jacques C.; Doyle, Martin W. Comparison of morphological and biological control of exchange with transient storage zones in a field-scale flume J. Geophys. Res., Vol. 114, No. G2, G02019

Katsuyama, Masanori; Kabeya, Naoki; Ohte, Nobuhito Elucidation of the relationship between geographic and time sources of stream water using a tracer approach in a headwater catchment Water Resour. Res., Vol. 45, No. 6, W06414

Phillips, J.D. 2009. Landscape evolution space and the relative importance of geomorphic processes and controls. Geomorphology, 109:79-85.

And last but not least:

Pretty much all of: Hydrological Processes, Special Issue: Hyporheic Hydrology: Interactions at the Groundwater-Surface Water Interface. Issue Edited by Stefan Krause, David M. Hannah, Jan H. Fleckenstein. Volume 23, Issue 15, 2009.

Most especially this article:
Boano, F., Revelli, R., and Ridolfi, L. 2009. Quantifying the impact of groundwater discharge on the surface-subsurface exchange, Hydrological Processes, 23(15): 2108-2116.