Subject: How are Negative Transect Elevations Used in SWMM5?
You can have negative elevations in the Transects of SWMM 5 as the elevations are transformed internally to relative depths above the node inverts in the SWMM 5 engine (Figure 1). The slope of the link is calculated from the link offset elevations (Figure 3) and the cross sectional information for the irregular link in SWMM 5 (Figure 2) is computed from the Transect data (Figure 4). The Water Surface elevation of the link is based on the node inverts (Figure 5).
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Figure 1. Transect Editor of SWMM 5 |
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Figure 2. The Transect Data is Used in the Irregular of HEC-RAS Shape of SWMM 5 |
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Figure 3. The slope of the link with the Transect is calculated from the link upstream and downstream offset elevations – not the Transect data which is relative. |
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Figure 4. Transect Data Transformed into Tables of Area, Hydraulic Radius and Width from the Transect Data internally in SWMM 5. |
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Figure 5. HGL of the Water Surface Elevation from the Node Invert and Link Offset Elevations. |
