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Monday, May 16, 2011

Fluvial Geomorphology and Flood Hydrology: from a webpage from my alma mater, Southern Illinois University, work by Professor Nicholas Pinter

Fluvial Geomorphology and Flood Hydrology:
Recent floods worldwide have led to suggestions that flooding has become more frequent and more severe on many rivers. Rigorous documentation of hydrologic change is challenging because long-term trends are superimposed on short-term fluctuations and because causal mechanisms operate simultaneously and their effects are difficult to quantitatively separate. The emphasis of research in "empirical hydrology" at SIU is on quantifying observed changes in the magnitude and frequency of flooding due to specific natural and anthropogenic modifications of river systems.
In spite of up to $1.1 billion annually spent on flood-control infrastructure, economic damages from floods in the U.S. have risen dramatically during the 20th century. Most researchers agree that the principal mechanism driving up disaster damages is development in high-risk areas such as floodplains, but a second set of mechanisms involves active "forcing" of the magnitude or frequency of hazardous natural processes. There is widespread anecdotal evidence that the physical phenomenon of flooding has increased in magnitude and frequency on many rivers. Worldwide, systematic increases in runoff and/or flooding have been noted on rivers in Kenya, Poland, Japan, Germany, and elsewhere. Along the Lower Missouri River and the Mississippi near St. Louis, increases in flood levels of up to 3-4 m during the past century have been documented.
There are three principal sets of mechanisms by which the physical severity of flooding may systematically rise over time: (1) land-use change, (2) climate shifts, or (3) engineering activities and structures along rivers themselves. Urbanization alters the pathways and velocities at which rainfall runs off the landscape, typically increasing small stream flooding, although this process seems to affect floods on large rivers little. In contrast, regional conversion of watershed land, especially to agriculture, seems to have impacted even the largest U.S. rivers in the past 1-2 centuries. In addition, long-term climate change may be altering precipitation patterns and bringing increased likelihoods of large rainfall events to U.S. drainage basins.

The third set of mechanisms that can worsen flood disasters over time are engineering activities and structures in rivers and their floodplains. These mechanisms do not typically result in increased flood flows (discharges), but rather they decrease the conveyance capacity of the channel and thus result in higher water-surface elevations (stages). These mechanisms can be subdivided into: (1) channelization and other navigation-improvement activities, and (2) levee construction and other flood-control activities. On the Missouri River, channelization during the past ~100 years has been repeatedly linked to channel capacity losses. At measurement stations spanning >1000 km from the lower Missouri to the middle Mississippi rivers, increases of up to 3-4 m have been linked to the construction of navigational engineering structures and levees. On the Rhine River, numerical modeling by the Dutch government has shown that navigational groins (wing dams) increase flood stages and that groin lowering can be an effective tool for significantly lowering flood levels.
Selected Papers
Pinter, N., B.S. Ickes, and J.H. Wlosinski, in press. Contrasting trends in flooding on the Mississippi and Rhine river systems. Submitted to Journal of Hydrology.
Pinter, N., R.R. van der Ploeg, P. Schweigert, and G. Hoefer, 2006. Flood Magnification on the River Rhine. Hydrological Processes, 20: 147-164.
Pinter, N., 2005. Policy Forum: Floodplain encroachment since the 1993 flood. Science, 308: 207-208.
Pinter, N., and R.A. Heine, 2005. Hydrodynamic and morphodynamic response to river engineering documented by fixed-discharge analysis, Lower Missouri River, USA. Journal of Hydrology, 302: 70-91.
Pinter, N., K. Miller, and J.H. Wlosinski, 2004. Recurrent shoaling and dredging on the Middle and Upper Mississippi River, USA. Journal of Hydrology, 290: 275-296.
Pinter, N., and R. Thomas, 2003. Engineering modifications and changes in flood behavior of the Middle Mississippi River. In R. Criss and D. Wilson, (eds.), At The Confluence: Rivers, Floods, and Water Quality in the St. Louis Region, pp. 96-114.
Pinter, N., R. Thomas, and J.H. Wlosinski, 2002. Reply to U.S. Army Corps of Engineers Comment on "Assessing flood hazard on dynamic rivers." Eos: Transactions of the American Geophysical Union, 83(36): 397-398.
Pinter, N., J.H. Wlosinski, and R. Heine, 2002. The case for utilization of stage data in flood-frequency analysis: Preliminary results from the Middle Mississippi and Lower Missouri River. Hydrologic Science and Technology Journal, 18(1-4): 173-185.
Pinter, N., R. Thomas, and J.H. Wlosinski, 2001. Flood-hazard assessment on dynamic rivers. Eos: Transactions of the American Geophysical Union, 82(31): 333-339.

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