Class Notes (835,503)
Canada (509,212)
EARTHSC 2GG3 (199)
Lecture

Earth Science - Lecture 34 Notes.docx

4 Pages
126 Views
Unlock Document

Department
Earth Sciences
Course
EARTHSC 2GG3
Professor
Sergei Basik
Semester
Fall

Description
November 22, 2013 FLOOD FREQUENCY AND FLOOD RELATED HAZARDS Flood Frequency Recurrence Interval  Recurrence interval: o Represents frequency of a natural disaster as an average time between past events o Helpful when natural events are random o Also called return time  Flood frequency is recorded as recurrence interval: o Average time between floods of a given size o Larger flood discharges on given stream have longer recurrence interval between floods  Calculated recurrence interval depends on: o Total number of years in flood o Record of rank of flood  Any new larger flood reduces rank and thus reduces recurrence interval  For a given-size flood, recurrence interval is: o T = (n+1)/m o T = recurrence interval o n = total number of years in record o m = rank of flood (largest flood = 1; second largest flood = 2, etc.) Ex. If the largest flood on a rivet at a single location was in 1997 and there are 87 years of records, what is the recurrence interval for the 1997 flood? m 1997= 1 n = 87 T1997= (87+1)/1 = 88 years Ex. If in 2007 a slightly larger flood occurs, what is the corrected recurrence interval for 1997? m 2007= 1 and m1997= 2 T1997= (97+1)/2 = 98/2 = 49 years Problems with Recurrence Intervals  Data for recurrence interval must cover interval long enough to be representative  Assumes that upstream conditions were similar through time: o Climate changes o Anthropogenic factors (urbanization, dams, deforestation, etc.)  All floods plotted should originate from similar causes for random distribution of flood sizes November 22, 2013 100-year Floods  100-year flood used to establish regulations for buildings near streams  100-year flood has 1% change of happening in any given year (including after a similar event)  Term 100-year flood is misleading because it leads people to believe that it happens only once every 100 years  Better term would be: “1-in-100 chance flood”  100-year floodplain: o Area likely to be flooded by largest event in 100 years (on average) o Based on extrapolation from few large recorded events o Does not account for probable changes from upstream alterations to drainage basin (human activities) Paleoflood Analysis  Short record of stream flow data is major problem  Use physical evidence of past flooding that is preserved in geologic record to reconstruct approximate magnitude and frequency of major floods  Estimated paleoflood magnitude or flood height  Critical info on minimum hazard of past flood Early post-flood evidence (Paleoflood markers):  Nature and magnitude of flood is most obvious immediately afterward  Useful features include features indicating height, velocity and size of flood: o High-water marks o Cross-sectional area o Mean flood depth o Estimated water velocity o Mean flow velocity o Discharge Dendrochronological method (tree ring damage):  Trees may preserve effects of damage from flood and indicate number of years since damage  Height on tree indicates minimum hei
More Less

Related notes for EARTHSC 2GG3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit