Summary for Friday January 29th

Today, we started with a look at Major US cities that are not situated near large bodies of water. of the top ten, three could be considered extraordinarily dry (San Antonio, Dallas, and Phoenix) with Phoenix and its usually dry Salt River the largest. Other major (top 30) US cities with tiny rivers (500 cfs average in January) include: Austin, Fort Worth, El Paso, Denver, and Las Vegas.

We then discussed the calculation of recurrence interval for a given location (our homework for the weekend) and how this recurrence interval is used to better understand the likelihood of rare events (such as large floods). On thing that I forgot to mention in lecture was a quote from our reading The force of nature By Jacob Geiger

"As the name suggests, 100-year storms should happen once each century. But Rockbridge County has seen four of those storms, and the flooding that results from them, in the last seven decades."

The idea expressed here is that a the size of a 100-year event is somehow stamped in concrete for a particular river or section of river and will remain constant for time and all eternity. As we amass more data and develop a better understanding of the complexities of particular natural systems, we need to recognize that our perceptions must change to accommodate the facts. Thus, if you have, say four 100-year events in 70 years- particularly for an area that has only been systematically measuring these things for about 70 years, you need to change your definition of a 100-year event.

Flood plain maps are an important application of recurrence interval and topographic information. FEMA is the US government agency that is in charge of creating and distributing 100- and 500-year events. You can find a flood plain map for much of the US by here. We looked at flood plains maps for Lex and BV and discussed the differences between the two.

Calculating recurrence interval and making flood plain maps are both examples of passive mitigation- that is, reducing the impacts of disasters through studying and understanding the natural and human systems involved. Active mitigation, as the name would imply, involves actually doing something about the hazard. We discussed the creation of infrastructure (levees, floodwalls (such as the one in BV), flood protection dams such as the Goshen Dam and the Surrey Dam)and (re)positioning infrastructure and the different responses of three local communities (Lex, BV, and Glasgow) to active flood mitigation. In the contexts of flood mitigation, we also briefly discussed why people choose to inhabit floodplains (because floodplains are awesome- aside from the flooding part) the role of zoning laws and insurance in controlling these choices. If you are interested in reading more about flood insurance, there is more than any reasonable person would want to know here. Finally, we briefly touched on evacuation.

On Monday, we will discuss the Johnstown flood of 1989. For lecture on Monday, Please read:

Research at the Source of a Pennsylvania Flood by Henry Fountain- a brief introduction to an audio interview with Carrie Davis Todd. The audio can be accessed along the left margin of the page. The portion that is relevant to the flood is from 13:14 to go to 7:49 to go. You do not have to listen of the rest of the audio presentation.

PowerPoint slides shown in lecture today are now available as a .pdf on Sakai.

The my maps page has been updated with the locations mentioned in today's lecture.

Do not forget that there is a homework assignment due on Monday. I will be available in our classroom 8:00 pm Sunday evening to meet with anyone who is having or anticipates having difficulties completing the assignment.