Instead, some period of time will elapse before the main refills and can then start obeying "outflow equals inflow".
PCSWMM 7.1 FULL
Thus the main no longer remains full throughout its length, so when the pump cycles on again, the flow at the pump will not be immediately seen at the outlet since the main is no longer pressurized throughout. During the time that the pump is off but the main keeps discharging water, mass continuity says that somewhere along the main there must be empty volume that becomes available to make up for the volume being discharged. This is simply Newton's Second Law at work (a body in motion tends to stay in motion unless subjected to an opposing force). The momentum contained in this column of water will continue to carry it out of the downstream end, until such time that frictional forces dissipate its forward motion. When the pump shuts off, the water in the main is moving at about 2 ft/sec. Note that during periods of prolonged pumping, when the main remains fully pressurized, the outflow from the main is perfectly matching the varying inflow from the pump.Īn objection has been raised about this behavior, based on the belief that once the main is pressurized, the outflow should equal the inflow at every instance of time, including those times when the pump is turned off (implying that the main will not de-pressurize during such times).
PCSWMM 7.1 SERIES
If you run this example, graph the time series of flows for the pump and the last force main segment with the X-axis interval adjusted to focus on the period from 16 to 18 hours so you can more easily observe the behavior just described.
![pcswmm 7.1 pcswmm 7.1](https://i.ytimg.com/vi/NLt3ZzKMZgg/maxresdefault.jpg)
![pcswmm 7.1 pcswmm 7.1](https://d3pcsg2wjq9izr.cloudfront.net/files/28837/video/1037063/28837_20_202108190834429062998_thumbnail_Auto.jpg)
A typical diurnal DWF pattern is fed into the pump's wet well and the Type 3 pump turns on at 5 feet and turns off at 1 feet. A fixed downstream boundary condition with water level 0.1 ft above the top of the force main is used.
![pcswmm 7.1 pcswmm 7.1](https://ars.els-cdn.com/content/image/1-s2.0-S1470160X18304461-gr5.jpg)
It has a 50,000 foot long flat force main divided into 10 conduit sections of 5,000 feet each. The input data for an example showing this behavior is listed below. The net result is that the initial flow rate seen at the pump when it turns on again is significantly attenuated at the outlet of the main. When the pump starts up again, there is a lag and then a gradual increase in flow out of the main for several minutes until such time as the main completely re-fills and re-pressurizes once again. This causes it to de-pressurize at some point along its length since flow is leaving but not entering the main during this period of time. When the pump shuts off, SWMM shows that flow continues to exit from the end of the force main for several minutes at a decreasing rate.
![pcswmm 7.1 pcswmm 7.1](https://www.mdpi.com/water/water-11-02583/article_deploy/html/images/water-11-02583-g007.png)
The results demonstrate that OSTRICH-SWMM is a promising tool for automatic calibration of SWMM models.It has been brought to my attention that several users do not believe that SWMM 5 is correctly simulating the behavior of a long, pumped force main during times when the pump rapidly cycles on and off. The Pareto front for the case study was obtained using a multi-objective calibration algorithm and this allowed for evaluating tradeoffs between the peak flow and total volume criteria. A catchment in Buffalo, NY was selected as a case study and was calibrated according to two competing criteria: (1) minimizing errors in simulated peak flow, and (2) minimizing errors in total flow volume. The newly developed OSTRICH-SWMM is an open-source tool with dozens of parallelized optimization algorithms.
PCSWMM 7.1 SOFTWARE
In this study, SWMM was integrated with the Optimization Software Tool for Research Involving Computational Heuristics (OSTRICH) to perform single- and multi-objective automatic calibration. Consequently, model calibration is a challenging task. A typical SWMM project has hundreds or thousands of sub-catchments and more than 20 parameters associated with six different physical processes for each sub-catchment. The USEPA (United States Environmental Protection Agency) Storm Water Management Model (SWMM) is one of the most widely used numerical models to simulate urban runoff and drainage.