Assignment
III (3 pt extra credit on exam 3)
Recurrence
Interval of Flooding
due:
November 29th at the
beginning of class
The purpose of this assignment is to allow you to determine the frequency of flooding along the Brazos River in the vicinity of Simonton, Texas, just south of Sealy. Floods in 1991 and 1994 caused serious damage in the Simonton area. Before any analysis can be done to evaluate alternative methods of flood control, the recurrence interval of these two floods must be determined. Unfortunately, there is no gaging station at Simonton. For this reason, we must use historical discharge data obtained from the Richmond gaging station, where Highway 59 crosses the Brazos River, approximately 12 miles downstream from Simonton.
You must first rank the maximum annual discharge data provided in the table below from largest to smallest. You then need to determine the recurrence interval (RI) of each flood, where:
RI = N+1 / m
N = total number of years of record
m = rank (largest = 1)
and
P = 1/ RI
P = annual exceedence probability
|
Water Year |
Max. Discharge |
Rank (m) |
R.I. (yrs) |
Annual Probability |
|
1923 |
54900 |
|
|
|
|
1924 |
64800 |
|
|
|
|
1925 |
24200 |
|
|
|
|
1926 |
86900 |
|
|
|
|
1927 |
42500 |
|
|
|
|
1928 |
36800 |
|
|
|
|
1929 |
123000 |
|
|
|
|
1930 |
78800 |
|
|
|
|
1931 |
52100 |
|
|
|
|
1932 |
80500 |
|
|
|
|
1933 |
34000 |
|
|
|
|
1934 |
71400 |
|
|
|
|
1935 |
90900 |
|
|
|
|
1936 |
74700 |
|
|
|
|
1937 |
77100 |
|
|
|
|
1938 |
68600 |
|
|
|
|
1939 |
41900 |
|
|
|
|
1940 |
82100 |
|
|
|
|
1941 |
117000 |
|
|
|
|
1942 |
79400 |
|
|
|
|
1943 |
45500 |
|
|
|
|
1944 |
93800 |
|
|
|
|
1945 |
85000 |
|
|
|
|
1946 |
82500 |
|
|
|
|
1947 |
51000 |
|
|
|
|
1948 |
22100 |
|
|
|
|
1949 |
56000 |
|
|
|
|
1950 |
44500 |
|
|
|
|
1951 |
11100 |
|
|
|
|
1952 |
34400 |
|
|
|
|
1953 |
83100 |
|
|
|
|
1954 |
32400 |
|
|
|
|
1955 |
19300 |
|
|
|
|
1956 |
17900 |
|
|
|
|
1957 |
119000 |
|
|
|
|
1958 |
87600 |
|
|
|
|
1959 |
39200 |
|
|
|
|
1960 |
60300 |
|
|
|
|
1961 |
78800 |
|
|
|
|
1962 |
20600 |
|
|
|
|
1963 |
17400 |
|
|
|
|
1964 |
14400 |
|
|
|
|
1965 |
98800 |
|
|
|
|
1966 |
74400 |
|
|
|
|
1967 |
13400 |
|
|
|
|
1968 |
89600 |
|
|
|
|
1969 |
58100 |
|
|
|
|
1970 |
47800 |
|
|
|
|
1971 |
20100 |
|
|
|
|
1972 |
24400 |
|
|
|
|
1973 |
72500 |
|
|
|
|
1974 |
55300 |
|
|
|
|
1975 |
64000 |
|
|
|
|
1976 |
44300 |
|
|
|
|
1977 |
80500 |
|
|
|
|
1978 |
16100 |
|
|
|
|
1979 |
88100 |
|
|
|
|
1980 |
45500 |
|
|
|
|
1981 |
64700 |
|
|
|
|
1982 |
61300 |
|
|
|
|
1983 |
58600 |
|
|
|
|
1984 |
10600 |
|
|
|
|
1985 |
36400 |
|
|
|
|
1986 |
45600 |
|
|
|
|
1987 |
67800 |
|
|
|
|
1988 |
17100 |
|
|
|
|
1989 |
43800 |
|
|
|
|
1990 |
55800 |
|
|
|
|
1991 |
51400 |
|
|
|
|
1992* |
94000 |
|
|
|
|
1993 |
60100 |
|
|
|
|
1994 |
34000 |
|
|
|
|
1995* |
88100 |
|
|
|
|
1996 |
24700 |
|
|
|
|
1997 |
61200 |
|
|
|
|
1998 |
53000 |
|
|
|
|
1999 |
80300 |
|
|
|
|
2000 |
14600 |
|
|
|
|
2001 |
46700 |
|
|
|
|
2002 |
523300 |
|
|
|
|
2003 |
74800 |
|
|
|
1) Determine the recurrence interval and annual
probability for all floods over 80,000 cfs.
2) What is the probability of a flood at
least as big as the 1995 flood occurring in the next 12 months from now?