Environmental Engineering Reference
In-Depth Information
FIGURE 4.19
Notepad view of PeakFQ output table for Mud Creek.
10
4
Bull. 17-B frequency
Systematic peaks
Systematic frequency
Confidence limits
10
3
Peakfq 5 run 9/23/2008 15:55
Note: Preliminary computation
User is responsible for
assessment and interpretation.
10
2
99.5
98
95 90 80 70
Annual exceedance probability (%)
Station - 02430615 Mud Creek near Fairview, MS
50
30
20
10
5
2
1
0.5
0.2
FIGURE 4.20
PEAKFQ graphic plot for Mud Creek near Fairview, Mississippi.
or equal to 12 cfs. This extreme low analysis can be computed similarly to the peak lows, assum-
ing a Log-Pearson Type III distribution, but using the left (low probability) side of the frequency dis-
tribution. A program supported by the U.S. EPA for the computation of
X
Q
T
lows from historical
records is DFLOW. DFLOW directly incorporates the USGS SWSTAT Program (Program A193)
that statistically analyzes time-series data and uses the Log-Pearson Type III estimation method.
DFLOW also allows for the calculation of biological as well as hydrology-based design lows as
described in Technical Guidance Manual for Performing Wasteload Allocations: Book VI: Design
Conditions: Chapter 1: Stream Design Flow for Steady-state Modeling (USEPA 1986).
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