CE 374K Hydrology Homework Assignment #8

**Flood Frequency
Analysis**

The attached spreadsheet
guadpeak.xls
and comma separated file guadpeak.csv
contain the annual maximum discharges of the Guadalupe River at Victoria for
the period 1935 – 2000. These data are
also obtainable in the LRC in /class/maidment/ce374k00. Actually these data are
for water years, which begin on October 1 of the previous year and continue to
September 30 of the current year.
These data were obtained from the *Peak Flow* file at http://waterdata.usgs.gov/tx/nwis/peak
for USGS Station 08176500. The data
for 1935 to 1998 are plotted below. In
October 1998, an enormous flood occurred on the Guadalupe River (in the 1999
water year) for which the discharge has been estimated by the USGS as being
466,000 cfs. This is not shown on the
graph below to avoid making all the other floods seem very small.

(1) Plot a graph of all the data, including the flows in 1999 and 2000.

(2) Estimate the return period of annual maximum discharges which exceed 30,000, 40,000, 50,000, and 60,000 cfs directly from the data by looking at the recurrence interval between flows exceeding those magnitudes in the data from 1935-2000.

(3) Take the logs to base 10 of the data and calculate their mean, standard deviation and coefficient of skewness for the data from 1935 – 1998, and also including the last two years of data, i.e. 1935-2000.

(4) Estimate the 100 year flood on the Guadalupe River using the Log normal (if coefficient of skewness ~ 0) or Log Pearson III method (if coefficient of skewness is significant). By how much does the inclusion of the October 1998 flood increase the 100 year flood estimate?

This assignment is due on Tuesday April 10