HydroTools has been tested using the Fishkill Creek example in "Guidelines for Determining Flood Flow Frequency" (Bulletin 17B of the Hydrology Committee, U.S. Geological Survey, Reston, VA). The annual peak flow data given below.
Using a skew coefficient of 0.7, the reported value for the 100-year discharge is 1150 cfs. Using the HydroTools LogPearson() function without specifying the skew coefficient (and thus having it estimated from the observed annual peak discharges), the estimated 100-year flood is 1170 cfs. Specifying the skew coefficient to be 0.7 (to match the published analysis), the estimated 100-year discharge is 1160 cfs. The slight difference between the published value and that estimated using the LogPearson() function reflects rounding errors.
The published value for the 1.01-year discharge is 841 cfs with 95% confidence limits of 568 cfs and 1100 cfs. Using the HydroTools LogPearson() function with a skew coefficient of 0.7 and the confidence limits of 0.95, the estimated 1.01 year discharge is 838 cfs with lower and upper confidence limits of 565 cfs and 1092 cfs. Again, the light difference between the published value and that estimated using the LogPearson() function reflects rounding errors.
Year Annual Peak Discharge (cfs)
1945 2290
1946 1470
1947 2220
1948 2970
1949 3020
1950 1210
1951 2490
1952 3170
1953 3220
1954 1760
1955 8800
1956 8280
1957 1310
1958 2500
1959 1960
1960 2140
1961 4340
1962 3060
1963 1780
1964 1380
1965 980
1966 1040
1967 1580
1968 3630