Hi
I've set up a pretty straight forward model that involves a storage node with a pump deilvering to a force main which discharges to a gravity main. Gravity main has an orifice at the end to deliver about 60l/s. Pump cut in at 2.1 depth cutout at 1.5. Preliminary numbers on the pump done manually suggest a duty of about 110l/s@10m. Baseflow into the storage node is set at 67l/s ie pump should cycle and therefore the gravity main should empy also. The results however dont show this as the gravity line fills but never empties.
Help please!
Replies
yes that the version and yes it is that SWMM build
You perhaps can see this more clearly if I reduce the lengths of your links so that the total volume of the links is less than the inflow volume at the wet well, the orifice then reacts faster to the pump
Hi, I am getting very different answers than you show in the model current.inp, is that the actual version you used to make the graphs and are you using SWMM 5.0.022?
I am now getting some flows by using many save and use hot start iterations, the problem with the draining in your model is the amount of storage in your system - which is 3 times the inflow volume
************************** Volume Volume
Flow Routing Continuity hectare-m 10^6 ltr
************************** --------- ---------
Dry Weather Inflow ....... 0.000 0.000
Wet Weather Inflow ....... 0.000 0.000
Groundwater Inflow ....... 0.000 0.000
RDII Inflow .............. 0.000 0.000
External Inflow .......... 0.011 0.108
External Outflow ......... 0.011 0.108
Internal Outflow ......... 0.000 0.000
Storage Losses ........... 0.000 0.000
Initial Stored Volume .... 0.037 0.375
Final Stored Volume ...... 0.036 0.365
Continuity Error (%) ..... 2.043
You have the same total flow at all of your junctions and outfall that you have as an input, the storage of the links above the orifice are what is controlling the reaction of the outflows.
I've set the system up pretty much as outlined above. We have an orifice just before the outfall with the intention of limiting the outflow downstream to somewhere about 60l/s. Based on inflow to the pumpwell of 60 l/s and pump duty of110l/s the pump still cycles. My problem is that the gravity system never seems to empty and even if I put a ridiculous orifice width in, the discharge through the system seems insensitive to the size of the orifice (see attached). If I drop the inflow and pump outputs to 10l/s and 20l/s the system still does not empty (attached also). I am unsure why this is happening and why the insentivity to orifice size
If you add a break node about 95 percent of the distance along the long force main you get a better response for the gravity mains to the pump, the force main flows about equal the pump flows
A few suggestions:
1. Use a hot start file to warm up you system,
2. Use a flap gate in the long force main
3. The pump and long force main look good but the gravity mains (which you have as force mains) do not drain see this image