The four cross sectional areas in a link of SWMM 5 and InfoSWMM

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

Possible Link Graph and Computational Variables

The 4 Areas of a  Link in SWMM 5 - Rising Limb

The 4 Areas of a  Link in SWMM 5 - Rising Limb and Falling Limb


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