Posts Tagged ‘flooding’

Flood frequency changes

Tuesday, June 14th, 2011

June 2011 Article: “Examining Flood Frequency Distributions in the Midwest U.S.,” by Gabriele Villarini, James A. Smith, Mary Lynn Baeck, and Witold F. Krajewski. Part of Featured Collection on “Nonstationarity, Hydrologic Frequency Analysis, and Water Management.”

Annual maximum peak discharge time series from 196 stream gage stations with a record of at least 75 years from the Midwest United States is examined to study flood peak distributions from a regional point of view. Change-points rather than monotonic trends are responsible for most violations of the stationarity assumption. The abrupt changes in flood peaks can be associated with anthropogenic changes, such as changes in land use?land cover, agricultural practice, and construction of dams. The trend analyses do not suggest an increase in the flood peak distribution due to anthropogenic climate change.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Getting from here to there

Friday, June 10th, 2011

June 2011 Article: “Getting From Here to Where? Flood Frequency Analysis and Climate,” by Jery R. Stedinger and Veronica W. Griffis. Part of Featured Collection on“Nonstationarity, Hydrologic Frequency Analysis, and Water Management.”

The authors note, “Flood-risk computations by United States (U.S.) federal agencies follow guidelines in Bulletin 17 for which the latest update 17B was published in 1982. Efforts are underway to update that remarkable document. Additional guidance in the Bulletin as to how to address variation in flood risk over time would be welcome.”

If stationarity is dead, what should we do? The authors address this question by showing some possible ways Bulletin 17 could be modified to account for some concepts of climate change. They don’t reject the value of historical data, but realize we can’t take it at face value: “Does climate change mean we are not interested in historical records? Of course not: historical data tell us what flood series look like and help us to estimate where we start. We then need to estimate what would change, which describes where we go from there. The critical concern is whether the contribution of nonstationarity to our uncertainty is large enough, and the signal sufficiently clear, that we would do better by including it in our analyses.”

They conclude, “In water-supply management, we often use period-of- record planning, which hides uncertainty. Now with climate change, we need to project from the uncertainty of our current knowledge based upon the past record to estimate the risk in the future. … Change in flood risk is not new.”

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Flood magnification

Wednesday, June 8th, 2011

June 2011 Article: “Nonstationarity: Flood Magnification and Recurrence Reduction Factors in the United States,” by Richard M. Vogel, Chad Yaindl, and Meghan Walter. Part of Featured Collection on“Nonstationarity, Hydrologic Frequency Analysis, and Water Management.”

This study takes a different approach by exploring trends in floods in watersheds which are subject to a very broad range of anthropogenic influences, not limited to climate change. A simple statistical model is developed which can both mimic observed flood trends as well as the frequency of floods in a nonstationary world. Nonstationarity in floods can result from a variety of anthropogenic processes including changes in land use, climate, and water use, with likely interactions among those processes making it very difficult to attribute trends to a particular cause.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Urban Drainage Networks Matter

Tuesday, August 24th, 2010

October 2010 Article: Analyses of Urban Drainage Network Structure and its Impact on Hydrologic Response, by Katherine L. Meierdiercks, James A. Smith, Mary Lynn Baeck, Andrew J. Miller

Urban flood studies have linked the severity of flooding to the percent imperviousness or land use classifications of a watershed, but relatively little attention has been given to the impact of urban drainage networks — including storm pipes, surface channels, street gutters, and stormwater management ponds — on hydrologic response. The authors demonstrate that drainage networks, like natural river networks, exhibit characteristic structures and that these features play critical roles in determining urban hydrologic response.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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Modeling an Extreme Flood in Texas

Monday, August 23rd, 2010

October 2010 Article: Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas, by Hatim O. Sharif, Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie2, Jon Zeitler.

"Flash Flood Alley"

One of the most flash flood prone areas in the U.S. is a region of South-Central Texas, called Flash Flood Alley (see figure) by local residents and weather experts. This dubious honor is the result of both climatic and geomorphic factors. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. This paper examines the meteorological conditions that led to this event and applies a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin.

The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration. Results of simulation by the distributed model demonstrate the advantage of using quality-controlled radar products, which typically better characterize the spatial and temporal distribution of rainfall than rain gauges.

[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]

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