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EPA SWMM5 supports near-surface groundwater processes (interflow) using two-compartment (unsaturated and saturated zones) aquifer objects that can interact with surface/subsurface hydraulic components.
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The recession limb of a flow hydrograph can especially exhibit the effect of groundwater. Under these situations, flow hydrograph may be significantly impacted by the contribution from groundwater. This is the case where there is a large proportion of pervious areas (with permeable soils) and in rural areas. While it is sufficient to consider only the overland flow runoff for many modeling situations, natural streamflow can combine both overland flow and subsurface flow. The only time I have not trusted EPANET’s modeling results is when I have gotten a message about the system not being stable.Interaction between surface water and groundwater is an important consideration under some hydrologic/hydraulic conditions.
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At this point, we can reduce the flow causing the warning or upgrade the piping system appropriately to deliver such flows. In summary, I believe EPANET generates the warning when the system is unable to meets a particular demand. This can be easily accomplished by filtering the data using the table icon. A good modeling practice is to check for extraordinary demands in the model prior to running a simulation.
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For this reason, prior to running a simulation I make sure that the model is set up as supposed to be.įor example, when performing fire flow simulations sometimes we forget to delete the fire demand at a node(s). Unless I’m testing at for rate of flow a transmission line’s air valve opens, I interpret this message as something wrong with my model. See Statutus Report for details” After we acknowledge it, by clicking on the OK bottom, the Status Report displays the warning: Negative pressures at xx hrs. I'm sure someone else from the List may share his/her experience or knowledge on this issue to complete answering your question.Īs you pointed out, sometimes after running a simulation EPANET displays a window with the following message: “ Warning messages were generated. pipe joints) or even worse, pipe internal collapse. However, this principle is used with gas chlorinators to dose chlorine to the outlet of reservoirs.įrom the cross connection standpoint, it is very important to keep feeding the break from the source of supply, until local isolation of the break is accomplished locally, to avoid developing negative pressure that may contaminate part of the system by the introduction of debris through small leaks (i.e. Normally, there are no vacuum gages in a water distribution system to measure the negative pressure. If we look at Bernoulli equation, the pressure head just transforms to velocity head during an event like that. Based on my experience while working as water supply operator and later on as hydraulic modeler, so far I find no reason not to trust the results of EPANET simulations when negative pressure is reported by the model.įor example, if a large water-main break occurs close to a pressure sensor, the telemetry may report zero pressure at this gage.