CE 374K Hydrology                 Homework Assignment on

Flood Frequency Analysis

The attached spreadsheet guadalupe.xls and comma separated file guadalupe.csv contain the annual maximum discharges of the Guadalupe River at Victoria for the period 1935 – 2002.   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 2002.

(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 1935-2002.

(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 four years of data, i.e. 1935-2002.

(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 27

 Annual Maximum Discharges of Guadalupe River at Victoria Date of Occurrence Year Peak Discharge (cfs) 6/20/1935 1935 38500 7/3/1936 1936 179000 10/4/1936 1937 17200 4/30/1938 1938 25400 6/6/1939 1939 4940 7/3/1940 1940 55900 5/3/1941 1941 58000 7/9/1942 1942 56000 10/21/1942 1943 7710 6/1/1944 1944 12300 4/6/1945 1945 22000 9/3/1946 1946 17900 10/17/1946 1947 46000 5/28/1948 1948 6970 4/30/1949 1949 20600 10/28/1949 1950 13300 6/8/1951 1951 12300 9/16/1952 1952 28400 5/4/1953 1953 11600 10/26/1953 1954 8560 5/22/1955 1955 4950 5/18/1956 1956 1730 5/2/1957 1957 35300 2/26/1958 1958 58300 4/15/1959 1959 10100 7/1/1960 1960 23700 6/22/1961 1961 55800 11/17/1961 1962 10800 2/21/1963 1963 4100 11/11/1963 1964 5720 2/21/1965 1965 15000 12/8/1965 1966 9790 9/21/1967 1967 70000 1/25/1968 1968 44300 4/13/1969 1969 15200 5/20/1970 1970 9190 9/12/1971 1971 9740 5/16/1972 1972 58500 6/17/1973 1973 33100 10/16/1973 1974 25200 5/29/1975 1975 30200 4/19/1976 1976 14100 4/24/1977 1977 54500 9/14/1978 1978 12700 5/12/1979 1979 19300 5/19/1980 1980 11600 9/2/1981 1981 105000 5/19/1982 1982 18500 11/20/1982 1983 10900 10/21/1983 1984 3280 4/21/1985 1985 10600 11/29/1985 1986 13700 6/7/1987 1987 83400 11/28/1987 1988 3900 5/21/1989 1989 4280 9/12/1990 1990 5230 4/5/1991 1991 17000 12/25/1991 1992 61500 6/30/1993 1993 17700 5/19/1994 1994 13300 10/19/1994 1995 39600 9/22/1996 1996 9760 4/4/1997 1997 32700 10/13/1997 1998 20600 10/20/1998 1999 466000 6/12/2000 2000 6220 9/3/2001 2001 39300 7/10/2002 2002 71700