Flows and Transport in Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 99

TABLE 4.3
Peak Flow Record for Mud Creek near
Fairview, Mississippi
Year Peak Flow (cfs) Year Peak Flow (cfs)

1976 613 1991 1390

1977 683 1992 1010

1978 631 1993 1510

1979 490 1994 843

1980 731 1995 1080

1981 196 1996 875

1982 497 1997 1080

1983 683 1998 NA

1984 760 1999 1040

1985 323 2001 907

1986 516 2002 815

1987 778 2003 489

1988 619 2004 800

1989 813 2005 830

1990 677 2006 737

where N is the number of peak lows and R is the rank (1 to N ), and then tabulate the probability for
each peak low as illustrated in Table 4.4.
First, it is apparent that the highest low in this record (1510 cfs) has a return period of only
30 years. Or, with 29 years of record, we can, using this speciic method, only directly compute the
low with a return interval of 30 years ( N + 1). So, to determine the 100-year lood, we would have
to extrapolate.
An alternative is to assume some probability distribution for the data. Flow data are typically
log-normally distributed and skewed and the statistical distribution typically used for peak-low
analyses is the Log-Pearson Type III distribution. To characterize that distribution, the statistics

TABLE 4.4
Peak Flow Probabilities for Mud Creek near Fairview, Mississippi
Rank

Prob. t r Peak Flow (cfs) Rank Prob. t r Peak Flow (cfs)

1 0.033 30 1510 16 0.533 1.9 737

2 0.067 15 1390 17 0.567 1.8 731

3 0.1 10 1080 18 0.6 1.7 683

4 0.133 7.5 1080 19 0.633 1.6 683

5 0.167 6 1040 20 0.667 1.5 677

6 0.2 5 1010 21 0.7 1.4 631

7 0.233 4.3 907 22 0.733 1.4 619

8 0.267 3.8 875 23 0.767 1.3 613

9 0.3 3.3 843 24 0.8 1.3 516

10 0.333 3 830 25 0.833 1.2 497

11 0.367 2.7 815 26 0.867 1.2 490

12 0.4 2.5 813 27 0.9 1.1 489

13 0.433 2.3 800 28 0.933 1.1 323

14 0.467 2.1 778 29 0.967 1 196

15 0.5 2 760