The Future of Big Rivers Colloquium Series

National Great Rivers Resesarch Education Center.

Organized by Jack and Richard Threet Professor of Sedimentary Geology: Dr. Jim Best. Sponsored by The National Great Rivers Research & Education Center, the University of Illinois and the Jack and Richard Threet Chair in Sedimentary Geology.

All lectures will be held at 5:00 PM in the Digital Computer Lab (DCL) room 1320.

OCT 8, 2014
Professor Phil Ashworth

University of Brighton, UK: Why Are the World's Big Rivers So Different?

Big rivers dominate the world's continental surface, yet we are still learning about how they operate and whether they are explicably different, not only from each other, but also from smaller rivers. Big rivers display an extraordinary range of channel pattern – much more so than smaller rivers. At the largest scale, trans-continent sized rivers do not possess unified valley systems created by fluvial erosion but instead involve chains of interlinked domains with contrasted fluvial functions. In natural states, big rivers can be plural systems in which it is accessory and tributary channels, rather than main-river branches, which determine patterns of floodplain morphology. The interplay between geomorphological and hydrological connectivity of components in big river plural systems determines habitat status and therefore ecological diversity.

Big rivers have a complex floodplain relief – both positive and negative. Negative relief is generated through differential erosion and sedimentation in three genetic zones: rheic, transitional and perirheic. It is the transitional zones marginal to active channels that generate the more varied form complexes. Active floodplain deposition by large rivers arises through a variety of processes within a general class of 'spillage sedimentation'. Presence and activity differ considerably: only some floodplains have prominent levees; some have coarse splays; others have thin tabular spreads of overbank fines. Many have channelized dispersion and reworking. Element dominance depends on diverse sediment loadings and flood discharges, but crucially also on prior floodplain relief and water status.

Although understanding of contemporary big river patterns requires attention to a range of timescales, including inheritance from sediments of Quaternary age, big rivers do have a distinctive character. Intra-river variability and internal complexity show the need to understand contrasted sediment supply, through-put and alluvial exchange as determinants of big river morphology and pattern.

NOV 11, 2014
Professor James Syvitski

University of Colorado, USA: New Possibilities in Monitoring and Modeling Hydrology and Sediment Transport for Global River Networks

(Co-authors: Sagy Cohen, Albert J. Kettner, and G. Robert Brakenridge) Global hydrological models have advanced over the last decade, from runoff predictions at 1° spatial resolution and one year time steps, to simulating runoff at 6 arc minutes and daily resolution (WBM model). In this model, flow routing employs a cell-tree topology and a semi-implicit finite difference solution to the Muskingum-Cunge equation using a diffusive wave solution to the St. Venant equations. Bankfull discharge is monitored for each pixel using a floodplain schema as described by Yamazaki et al. (2011) to simulate overbank flooding. Irrigational water demand is modelled with withdrawal from small reservoirs, shallow groundwater, nearby rivers, and unsustained deep aquifers. WBMsed takes into account landscape properties and landuse practices to simulate sediment load, sediment concentration, and sediment yield within the global river networks. Model implementation involves matching input resolution (time and space) with model resolution for global air temperature and precipitation, and appropriate boundary conditions (e.g. soil parameters, crop land, vegetation, bedrock lithology reservoirs, irrigation parameters, ice cover, population). Simulations provide both a continental view of the coupling between climate dynamics and the landscape, and the response from individual rivers. Human impacts on fluvial fluxes can also be quantified. The next decade should see improvements in both time and space resolution but will require new approaches in flow routing (kinematic or dynamic wave formulations), and higher resolution flow grids as well as refining sediment flux simulations by incorporating earthquake activity, more accurate land use changes, and improvements in simulating spatial bedload. Research possibilities are abundant: contributions to river characterizations and assessments, better understanding of coastal dead zones, and realistic coupling of climate dynamics to river morphology. Model compatibility to data from present and future satellite missions will further improve these efforts.

JAN 29, 2015
Professor Steven Goodbred Jr.

Vanderbilt University, USA: Constructing the Ganges-Brahmaputra Megadelta: From Process to Morphology to Stratigraphy

The Bengal basin of South Asia lies at the convergence of three tectonic plates, a position that has made it one of the principal repositories for Himalayan sediment over the past 40 million years. Today, the nearly 20-km thick pile of sediment remains the site of confluence for two great rivers of the world, the Ganges and Brahmaputra, which together drain 75% of the monsoon-drenched, tectonically active Himalaya. Delivering ~1 billion tons of sediment annually to the basin, these braided streams are laterally mobile and over the past few thousand years have constructed ~100,000 km² of low-lying delta plain. At the coast, the delta system interfaces with a dynamic marine environment at the head of the Bay of Bengal, where 3-m tides extend 100 km inland of the shoreline, along with storm surges from the nearly annual tropical cyclones. Sediment transported by these tides and marine incursions are essential to maintaining vast areas of the delta that receive little direct fluvial input. In addition to being geologically superlative, this massive river delta is also home 150 million people living in Bangladesh and West Bengal, India, giving the system great societal relevance, and strain. In this talk we will set the regional background of South Asia, and then connect modern processes to the current deltaic landform that has been built over recent millennia. From these surficial perspectives, we will then move below ground to investigate stratigraphic architecture of the >90-m thick Holocene delta, the development of which ensued promptly after end of the Younger Dryas cold period ~11,500 years ago.

MAR 13, 2015
Professor Matt Kondolf

University of California Berkeley, USA: The Mekong: Threats to a Unique Human-Ecosystem
The Mekong River is unique among the world's great rivers in the size of the human population supported by its ecosystem. Approximately 60 million people (mostly in Cambodia and Vietnam) derive at least part of their sustenance and their livelihoods from fish in the river system, although most of this is subsistence fishing so not captured by conventional economic statistics. Largely unregulated through most of the 20th century, the Mekong River system is undergoing extensive dam construction throughout the basin for hydroelectric generation, with over 140 dams planned, under construction, or built. What will be the cumulative effects of these dams on the geomorphology, ecology, and human populations of the river and its delta? How will these changes interact with other changes such as deforestation in steep uplands, levees and channelization, and accelerated sea level rise? Delineation of geomorphic provinces (as a basis for distributing sediment yields) and application of the 3W reservoir sediment trapping model indicates that if all dams are built as currently planned, they will block migration for important fish species, and will trap 96% of the river's sediment load formerly reaching the Mekong Delta, along with a large part of the nutrient load. The dams will lead to extinction of migratory fish species, and the reduc on in sediment and nutrient flux will have significant implications for ecosystem productivity and the persistence of the delta landform itself.

APR 27, 2015
Professor Andrew Nicholas

University of Exeter, UK: Computer Simulation of Large River Evolution
Numerical models provide a valuable framework for integrating understanding of fluvial processes and morphology. Moreover, models represent important tools with which to investigate river responses to environmental change and catchment management, and for aiding the interpretation of alluvial deposits and landforms. This talk aims to examine some recent advances in the development and application of numerical models for simulating river morphodynamics. It will then go on to consider some of the current barriers to progress, and areas requiring further attention in order that such models can be applied effectively to investigate river evolution. In doing so, it will touch upon a range of issues, including: model sensitivity to process parameterization and boundary conditions; representation of the diversity of river styles seen in nature; long-term coupling of river and floodplain processes; and the challenges associated with modelling river responses to past and future environmental change. The talk focuses in particular on large sand-bed rivers, although many of the issues to be examined are general problems relevant across a wide range of scales.