| Product(s): |
SewerCAD, SewerGEMS |
| Version(s): |
V8i, CONNECT Edition |
| Area: |
|
Problem
Using the GVF-Convex solver in SewerCAD or SewerGEMS, how are the results like flow and population computed downstream of a flow split (diversion rating table) when unit loads and extreme flow factors are involved?
Solution
Here is the general process:
1) In the node upstream of the diversion link, the total contributing population of all incoming pipes (plus any local loads) is added up and the extreme flow factor is computed based on the appropriate extreme flow method. This is done independently for all unique unit load types (you could have multiple different types entering from upstream manholes, each one could have a different extreme flow method associated with it).
2) The extreme flow factor is multiplied against the contributing base sanitary loads (unit load count time unit load) to acheive the total sanitary load entering the diversion
3) The total sanitary load is added to any incoming wet weather loads / infiltration to acheive the total flow
4) The total flow from step 3 is considered in the diversion rating table's "Upstream flow", and the corresponding "diverted flow" determines the flow split. From this split, a ratio is determined; the percentage that becomes diverted (flows down the diversion link) versus the percentage that flows down the other conduit.
5) To get a complete picture of the results of the diversion, view the results in the next downstream conduit. Meaning, do not look at the conduit directly downstream of the manhole from which the diversion splits off, but rather look at the next downstream conduit. Consider adding an intermediate node (transition or manhole) such that the immediate downstream pipe is short and no additional loads enter, to make it easy to observe the calculation and resulting flow split.
6) In the two downstream conduits, the computed total population will be the population at the diversion node (step 1) multiplied by the ratio (see step 4). For example for a total incoming population of 100, if the flow split is 75/25 with 25% diverted, then the population downstream of the diversion link is 25 and the population in the other conduit is 75.
7) Similarly, any incoming wet weather flows are split according to the same ratio.
8) With the new, smaller population from step 6, a new extreme flow factor is calculated in each conduit. If multiple unit load types had contributed, they will be split according to the proportion identified by way of the total flow split on the diversion rating table (step 4)
9) With the new extreme flow factor from step 8, (and new unit load count) a new total sanitary load is calculated in each of the downstream pipes. The sum of the two may be more than the total sanitary load at the upstream diversion node, due to the decrease in population at each downstream node.
10) The new total sanitary load from step 9 is added to the new split wet weather flow from step 7 to acheive the total conduit flow.
Below is a forum discussion where an example case is detailed - two incoming pipes and two outgoing pipes.
SewerGEMS+ Extreme load factor+DIversion