Manhole Elevations in InfoSWMM and SWMM 5

Subject: Manhole Elevations in InfoSWMM and SWMM 5

Starting from the bottom of the manhole you have these regions of computational interest:

1.   Manhole Invert to the lowest link invert – the node continuity equation is used with the area of the manhole being the default surface area of a manhole,

2.   Lowest Link Invert to the Highest Link Crown Elevation – the node continuity equation is used with surface of the node being normally half of the surface area of the incoming and outgoing links,

3.   Highest Manhole Pipe Crown Elevation to Manhole Rim Elevation – the node surcharge algorithm in which the surface area of the manhole is not used and the surcharge depth is iterated until the inflow and the outflows of the node are in balance,

4.   The region above the Manhole Rim Elevation which can use one of four options to calculate the depth and/or flow out of or into the manhole:

1.   No Surcharge Depth is entered and No Ponding area is used – the excess water into the manhole is lost to the network and shows up as internal outflow in the continuity tables,

2.   A Ponding Area is used and the excess flow will  pond on the surface of the manhole and later go back down into the conveyance pipes.

3.   A Surcharge Depth is used and the depth will continue to be calculated using the node surcharge algorithm in which the surface area of the manhole is not used and the surcharge depth is iterated until the inflow and the outflows of the node are in balance,

4.   A Dual Drainage system is simulated and the excess flow of the manhole is simulated in the street gutters or the actual street,

5.   You use a 1D/2D linkage between the 1D manhole and 1D links to a 2D Mesh and simulate the flow out and the flow into the manhole using a bottom outlet orifice that switches automatically between weir and orifice flow based on the depth on top of the manhole.

Pump / Force Main System in InfoSWMM and SWMM 5

Subject:  Pump / Force Main  System in InfoSWMM and SWMM 5

The basic system consists of:

·         Wet Well and its associated physical parameters,

·         Pump Type

·         Defined Pump Curve,

·         Downstream Pressure Node and

·         Downstream Force Main

Figure 1:  The Basic System

Step 1:  Wet Well Data

Enter the invert elevation, maximum depth of the Wet Well, the physical shape as either a function or shape table and any evaporation or infiltration.

Step 2:  Define the Pump Type

The pump type is defined by a Pump Curve and the On and Off elevations:

The four types of pumps are:

·         Volume - Flow

·         Depth – Flow

·         Head – Flow

·         Depth - Flow

Step 3:  Define the Pump Curve in the Operation Tab

Step 4:  Set a Surcharge or Pressure Depth at the Downstream end of the Pump

Any positive Surcharge Depth in the Node will allow the program during the simulation to keep the node under pressure forcing flow through the Force Main.

Step 5:  Force Main Data

Define the downstream pipe(s) from the pump as Force Main conduits with either a Hazen Williams or Darcy-Weisbach coefficient  (defined in the SWMM 5 options or the Run Manager of InfoSWMM)

Step 6: HGL Plot of the Force Main System

Step 7:  Pump Summary in the RPT File

 

 

Buildup/Washoff from a Subcatchment in SWMM 5

Subject:  Buildup/Washoff from a Subcatchment in SWMM 5

A pollutant concentration from a subcatchment in SWMM 5 can come from the precipitation, event mean concentration (EMC) in the washoff, rating curve washoff as a function of the surface runoff or power/exponential washoff from pollutants built up on the  land surface.  The pollutant washoff is mixed in the node and links for the network and can undergo first order decay, BMP or LID removal and  CSTR mixing.

Figure 1:  The COD buildup in pounds or kilograms from the initial loading, dry day loading and interevent loading.

Figure 2:  The COD Washoff based on the amount built up and the amount of runoff.

Figure 3:  The COD concentrations washing off the watershed based on the washoff equation, the runoff and the amount of buildup.

Figure 4.  COD Exponential Washoff and the Runoff from one Subcatchment.