Science spotlights

Science spotlights

Tucker receives Ralph Alger Bagnold Medal 2012

Science in the spotlight: June 2012 - July 2012

Ralph Alger Bagnold (1896-1990) started out his career as a royal military engineer, and spend much of his military career in North Africa and India exploring the desert and pioneering desert travel. He returned to science in 1944, and is most known in the earth sciences community for his contributions to the understanding of sand transport. Bagnold made significant contributions to the understanding of sedimentary structures such as sand dunes, ripples and sandsheets. He developed the dimensionless Bagnold number and well-known Bagnold formula, which relates sand transport to windspeed. Bagnold's passion for science never left him and he continued to publish scientific papers into his nineties. The R.A. Bagnold Medal commemorates his scientific achievements.

We quote the official European Geoscience Union statement on the 2012 Ralph Alger Bagnold Medal to Gregory Tucker: “Greg Tucker has made critical contributions to a large number of topics in geomorphology. He has been one of the pioneers in the use of two-dimensional landscape evolution models. He did not use them to study a particular issue or problem, but rather to explore how basic properties of geomorphic systems could be related to the landforms these systems produced, over a wide range of both temporal and spatial scales. By doing so, he has convincingly shown that geomorphic models that integrate all relevant processes can indeed make a decisive difference in furthering our understanding of landscape evolution. His work was seminal in showing how different processes may interact in order to produce, in some cases, unexpected and counterintuitive results, even when large landforms are considered. A prime example of this is one of his first publications on the modeling of the erosional dynamics of escarpments where he demonstrates that supply-limited conditions are a necessary prerequisite to produce high, long-lived escarpments. Widely cited modeling work of a few years later that he did together with Rafael Bras demonstrated that different assumptions on runoff and sediment production on hillslopes do indeed produce distinctive morphologies and drainage density-relief relationships. Together with Erkan Istanbulluoglo and others he also showed how vegetation potentially modifies long-term landscape response, a fact that is all too often forgotten in long-term landscape studies. Tucker’s contributions, however, are not limited to the study of soil-hillslope-drainage basin interactions. Together with Rafael Bras and others he went on to study the effects of event variability on landscape development, a welcome divergence of the steady-state assumptions that are used in most studies (Tucker and Bras, 2000). Variability has been an important theme in his work ever since Tucker conclusively showed that many aspects of drainage basin behaviour cannot be properly understood if temporal variability in the driving forces is not accounted for. Tucker has not modelled in isolation: throughout his career he has been interacting with field geomorphologists and he has been confronting models with empirical data wherever possible. This led to insightful papers on the factors controlling the development of arroyos (Tucker et al., 2006) as well as insights which may help guiding future erosion studies with cosmogenic nuclides in landslide-prone areas and the interpretation of geoarcheological archives. Finally, Tucker should not only be honoured for his important scientific contributions to geomorphology (the account above is but a small sample) but also for his clear scientific writing. Tucker’s papers excel in clarity, whereby things are looking simple, perhaps simpler than they really are. Many young scientists have been attracted to the theoretical aspects of our discipline through the papers of Tucker, and through the way he has made modeling tools like “Golem” and “Child” trademarks in the geomorphic community.”

References

• Gelfenbaum, G., Stevens, A.W., Elias, E., and Warrick, J.A., 2009. Modeling sediment transport and delta morphology on the dammed Elwha River, Washington State, USA. Proceedings of Coastal Dynamics 1-15, doi:10.1142/9789814282475_0109

Links

• Meet the Terrestrial Working Group Chair: Greg_Tucker

Elwha River restoration, the largest dam removal project in North America

Science in the spotlight: February 2012 - April 2012

Since the dams were built the Elwha River delta has experienced shoreline erosion, reduced sediment available to be moved along the coast via longshore transport, and a coarsening of the delta substrate. Gelfenbaum and others’ simulations predict post dam removal shoreline erosion rates may slow and even stop. A range of sediment sizes will accumulate at rates of up to 1 cm per year near the river mouth. Interestingly while sedimentation rates diminish away from the mouth of the river the tip of a nearby spit of land, Ediz Hook is modeled to receive increased sedimentation rates of approximately 0.5 cm per year. The stability of this hook is critical to the city of Port Angeles, that relies on the natural embayment created by it to provide a calm harbor for ships using the port of Port Angeles, and for others that use it to wait for favorable tides before proceeding on to other ports throughout the Puget Sound region.

References

• Gelfenbaum, G., Stevens, A.W., Elias, E., and Warrick, J.A., 2009. Modeling sediment transport and delta morphology on the dammed Elwha River, Washington State, USA. Proceedings of Coastal Dynamics 1-15, doi:10.1142/9789814282475_0109

Links

• A range of USGS publications on the Elwha River, including Gelfenbaum et al 2009 can be found at http://walrus.wr.usgs.gov/elwha/publications.html
• Link to animation of suspended sediment plume over 72 hour period http://pubs.usgs.gov/sir/2011/5120/5.13/player.html

Irreversible Peatland Subsidence Depends on Water Management

Science in the spotlight: November 2011 - January 2012

Bridge Foundation Exposed due to Subsidence

Understanding subsidence of peat-rich coastal areas due to bio-oxidation is of great importance, because of increased risk of flooding with rapid sea level rise, because of saltwater intrusion from nearby estuaries and lagoons, and because of net CO2 production with oxidation.
Detailed field observations of ground level and meteorological and soil conditions on peat-rich farmland nearby the Venice Lagoon in Italy over 2002-2006 show that with wetting and drying due to rainstorms significant, but reversible subsidence occurs. Peat expands with wetting and decreases as the water table drops subsequently. These elastic deformations due to pore pressure variations amount upto 5 mm over a few days to 2 weeks, and can be well modeled with a new numerical approach presented in the Journal of Geophysical Research paper (Zanello et al., 2011).
Irreversible loss over the period of measurement amounts upto 30 mm in 4 years. Subsidence has been ongoing over the last 70 years after this area was claimed for agricultural use. The exposed foundation of the small bridge on the photo illustrates how cumulative subsidence can be >1m, it now prohibits efficient drainage. A model quantifies the relationship between peat layer properties, water table (management) and temperature to predict bio-oxidation rates. It was found that most oxidation happens due to dry, warm conditions. The simulations indicate that for a given peat soil, oxidation is mostly influenced by a low water table levels. This result has important implications for hydrological management of peaty lowlands, less subsidence will occur under waterlogged conditions.

References

• Zanello, F., Teatini, P., Putti, M., Gambolati, G., 2011. Longterm peatland subsidence: experimental study and modeling scenarios in the Venice coastland. Journal of Geophysical Research, 116, F040002, doi:10.1029/2011JF002010

Links

• project website: Project website (mostly in Italian)..

New Modeling Textbook

Science in the spotlight: September 2011 - October 2011

Mathematical Modeling Cover

The newly published textbook: “Mathematical Modeling of Earth's Dynamical Systems: A Primer” by Slingerland and Kump helps earth scientists build essential skills to represent Earth surface processes with mathematical and computational models.
The book aims at upper-level undergraduate students, graduate students, and scientists who want to learn how to abstract complex earth systems into sets of dynamic equations. It is clear that the authors do aim at an audience that is familiar with the principles of physics, chemistry, and geology, and expect some background in differential and integral calculus. But the authors stress that little prior modeling experience is needed to use this book; they want to instill a philosophy of science that values quantification as a way of gaining insight. That philosophy rings true. The authors step aspiring modelers systematically through quantitative problem solving process. Firstly, get the physical picture clear while recognizing domains of interest and key factors, then write down the mathematical laws, be aware of the restrictive assumptions, check your units and boundary conditions and lastly verify, validate and solve your model.
Various relevant examples of processes and systems are provided with increasing complexity over the chapters. Slingerland and Kump offer problems over the entire Earth System Science domain in choosing groundwater flow, coastline evolution, sediment transport, radioactive decay, and carbon flux modeling problems as their rich set of examples. Every chapter has modeling assignments for eager modelers to try their newly acquired insight, or for teaching faculty to assign to their students. Slingerland and Kump are the “top chefs” who present a cookbook with their favorite basic recipes for earth surface modelers. Taste these, feed the inner quantitative modeler and enjoy.

The Princeton University Press quotes: "Written by two of the leading researchers in the field, Mathematical Modeling of Dynamical Systems is a must-read for all geoscientists, and not just students. This excellent primer offers bite-size gems of insight into the world of quantitative geosciences applications, covers both mathematical and modeling concepts, and offers practical exercises to build expertise. Course notes and methodologies will be improving across our academies."--James P. M. Syvitski, executive director, Community Surface Dynamics Modeling System

References

• Slingerland, R., Kump, L., 2011. Mathematical Modeling of Earth's Dynamical Systems: A Primer.
  

Princeton University Press. ISBN 978-0-691-14514-3.

Links

• Get it at the Princeton University Press site

Where do Salmon thrive?

Science in the spotlight: June 2011 - July 2011

Chinook Salmon

The Merced River in the Central Valley of California has been highly impacted by damming, gravel mining and placer mining over the last 150 years. River restoration projects along the Robinson Reach of the Merced River have focused on restoring the river to more natural conditions by excavating a 2.25km long single-thread, meandering channel with riffles and pools. Restoration was completed in January 2002. Dams in the upstream areas still dominate the flow conditions, with short releases of high water and mostly sustained low water. Two more extensive spring flood events with sustained overbank flows for several weeks occurred post-restoration.

A team of scientists from University of California, Santa Barbara, the California Polytechnical State University and the University of Wyoming used repeat observations of channel morphologies to condition flow simulations with FastMech-the Multidimensional Surface Water Modeling System developed by the USGS (a.o. Barton et al., 2005). Harrison and co-authors coupled the flow simulations to habitat criteria for Salmon spawning and rearing. Salmon prefer shallow riffles of ~50 cm for spawning, whereas optimal young salmon rearing habitat is in pools greater than 75 cm depth with lower flow velocities. Model simulations showed that substantial bar growth and migration occurred during the two flood events. Pointbars that were formed during flood are now favorable habitats at low flows, especially for spawning; 70% of the restored river stretch now has good habitat conditions for spawning. The coupled model predictions show that the restored channel has still less optimal conditions for Salmon rearing. Juvenile salmon need small-scale morphological features, which slow down the flow velocity.

References

• Harrison, L. R., C. J. Legleiter, M. A. Wydzga, and T. Dunne (2011), Channel dynamics and habitat development in a meandering, gravel bed river, Water Resour. Res., 47, W04513, doi:10.1029/2009WR008926.
• Barton, G. J., R. R. McDonald, J. M. Nelson, and R. L. Dinehart (2005), Simulation of flow and sediment mobility using a multidimensional flowmodel for the white sturgeon critical habitat reach, Kootenai River near Bonners Ferry, U.S. Geol. Surv. Sci. Invest. Rep., 2005‐5230.

Links

• Merced River restoration movie
  
• return of the salmon movie

Retreating Arctic Coasts

Science in the spotlight: April 2011 - June 2011

Coastline of North Alaska

The coastline in Arctic regions reacts to climate change with widespread increased erosion by 0.5 m per year. Coastal change is particularly dramatic in the Laptev, East Siberian and Beaufort Seas, where coastal erosion rates reach more than 14 m/year. Since around a third of the world’s coasts are located in the Arctic permafrost, coastal erosion may affect enormous areas in future. In general Arctic coasts react more sensitively to global warming than coasts in the mid-latitudes. Up to now these coasts have been protected against the eroding force of the waves, and warm sea water by sea ice cover. Due to the continuous decline in sea ice area extend, this protection is jeopardized.

Two thirds of the Arctic coasts consist of frozen sediments. And precisely these coasts are extremely hard hit by erosion. As a rule, Arctic regions are quite thinly populated. However, as nearly everywhere in the world, the coasts in the far north are important axes for economic and social life. The growing need for global energy resources as well as increasing tourism and freight transport additionally intensify anthropogenic influence on the coastal regions of the Arctic. For wild animal stocks, like the great caribou herds of the north, and the widespread freshwater lakes near the coast progressive erosion brings about significant changes in ecological conditions. More than thirty scientists from ten countries were involved in preparing the 170-page status report entitled “State of the Arctic Coast 2010”. The study was initiated and coordinated by the International Arctic Science Committee (IASC), the international joint project Land-Ocean Interactions in the Coastal Zone (LOICZ), the International Permafrost Association (IPA) and the Arctic Monitoring and Assessment Programme (AMAP) working group of the Arctic Council.

Links

• http://www.loicz.org/press/index.html.en
• http://www.arcticcoasts.org/
• PDF of report
• Article in 360 environment: As arctic sea ice retreats storms take toll on the land

Movies of coastal retreat can be found in the CSDMS EKT repository:

• Real_event_movies

Boom-and-bust cycles of barrier island retreat

Science in the spotlight: December 2010 - April 2011

Galveston Barrier Island, on September 9, 2008. Ike made its final landfall near Galveston, Texas. Galveston experienced a bust after a major 1900 storm, but recovered as a tourist resort from the 1930’s onwards. It remains vulnerable today.

Barrier Islands, the low-lying sandy strips separated from the coast by a lagoon, are a favorite location to build beach resorts. Whereas a natural barrier system would steadily migrate with sea-level rise, barriers evolution is now dynamically coupled to human action to prevent storm erosion. CSDMS scientist Dylan McNamara, currently at the University of North Carolina, has been on the forefront of coupled modeling of barrier island physical processes and human factors such as hazard mitigation driven by market development.

McNamara’s model shows that barrier island are maintained at unnaturally low elevations and that this situation filters out the frequent small responses to storm events, but that the inherently instability creates longterm boom-and–bust cycles of barrier island retreat.

References

• McNamara, D. and Werner, B., 2008. Coupled Barrier Island-Resort Model: 1. Emergent instabilities induced by strong human-landscape interactions. Journal of Geophysical Research – Earth Surface, 113, F01016, doi:10.1029/2007JF000840.
• McNamara, D. and Werner, B., 2008. Coupled Barrier Island-Resort Model: 2. Tests and predictions along Ocean City and Assateague Island National Seashore, Maryland. Journal of Geophysical Research – Earth Surface, 113, F01017, doi:10.1029/2007JF000841.

Links

• Dylan McNamara’s home page.