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Showing results for tags 'Surcharge'.
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Q: Is there an easier way to determine whether or not the manholes/gullies are surcharging other than using the EOF file, take the elevation of each MH, and take the max stage and compare the two together? A: When I want to visualise surcharging pits I load the mmQ layer and thematically map to see if there are any negative values in the Qmin column. I’ve popped an example in the first image below. You can do this by thematically mapping in MapInfo or using graduated styles in QGIS. You can so use the TuPlot plugin for QGIS to get more information on flows and how the pits are performing. Refer to the second image. Comments on how you visualise things most welcome!
Q: Why is the loss coefficient set to 1.56 when flow is surcharging against a bridge deck in a 1D bridge channel? A: The loss coefficient is derived from AustRoads, Waterway Design. Refer specifically to Figure 5.18 (pg 47, 1994 edition) (attached) The discharge coefficient, Cd, for a surcharging deck is 0.8, as shown highlighted in the attached figure Assuming that V=Q/(bn*Z) and rearranging the equation given at the bottom of the figure, one arrives at V=Cd* (2g* dh)^(0.5). Where bn is the net waterway width. Also given the loss formula used by the ESTRY engine dh=k*(V^2/2g), the final formula is k=1/(Cd^2). Thus, using a Cd of 0.8 as stated in AustRoads, k=1.5625.