Four Areas in a Link in SWMM 5

Note: Four cross sectional areas are used in a link of SWMM 5. The weighted hydraulic radius (Rwtd) is a function of the Froude Number of the link and the upstream and downstream hydraulic radius. The Rwtd value is used in the computation of the friction slope or the dq1 term in the file dynamic.c

dq1 = Time Step * RoughFactor / Rwtd^1.333 * |Velocity|

The weighted area (Awtd) is used in the dq2 term of the St. Venant equation:

dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) / Link Length

Time Base is T + T*K from the Time(T) and Storage (K) values

Note:  Each of the RDII UH’s has a base time for the convolution of the RDII from each UH.  The Time Base is T + T*K from the Time(T) and Storage (K) values  used in the RTK data.  In this particular case:

 ·         The Fast UH has a time base of 22 hours,

·         The Medium UH has a time base of 430 hours, and

·         The Slow UH has a time base of 4212 hours.

 If this is altered as in the  bottom image you can see the difference in the total  RDII I&I Flow

 ·         The Fast UH has a time base of 22 hours,

·         The Medium UH has a time base of 36 hours, and

·         The Slow UH has a time base of 52 hours.

H2OMAP-Sewer - FM Split Issue

Note:  One method would be to add a duplicate Wet Well/Pump/Force Main set of links to pass the flow from the upstream Force Main to the two downstream Force Mains (FM).  The pump should be fixed capacity to handle all of the split GM flows.  In this particular example the flows are split 50/50 to links 25 and 35 after leaving the loading manhole 24. 

Pumps and Force Mains in InfoSWMM

Note:  A pump is modeled in InfoSWMM somewhat akin to InfoSewer.  You have a Wetwell connected to a Pump which in turn is connected to a Force Main.  You can decide wheter a pipe is a Force Main or a Gravity Main by using the Atribute Browser and selecting Yes for Force Main and entering a FM Roughness.

 You can also use the PickAx tool in the Attibrute Browser to convert the node from a Manhole to a WetWell / Storage node.