Monday, July 11, 2011

Dry Weather Flow in SWMM 5

Subject:   Dry Weather Flow in SWMM 5

Dry Weather Flow in InfoSWMM and H2OMap SWMM

by dickinsonre
Dry Weather Flow in InfoSWMM and H2OMap SWMM 
Dry weather flow can be added to any node in H2OMAP SWMM.  The dry weather flow is computed as the average flow * the monthly pattern * the daily pattern * hourly pattern * the weekend daily pattern to give the Dry Weather Flow at any time step (Figure 1).   Since the four types of patterns (Figure 2) are all multiplied together then for Saturday and Sunday the hourly pattern and the weekend hourly pattern will both be used.   This will have the effect of overestimating the flow if the multipliers are greater than 1 and underestimating theflow if the multipliers are less than one.  You should enter the  Pattern X for the Weekend Hourly Pattern in H2OMAP SWMM  where 
X  = Weekend Hourly Pattern / Hourly Pattern 
So that when the pattern X is multiplied by the Hourly Pattern the program will use the intended Weekend Pattern. 
Figure 1.  How Dry Weather Flow is Computed in H2OMAP SWMM

Figure 2.  The Four Types of Time Patterns in H2OMAP SWMM, InfoSWMM and SWMM 5 

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