Flow and Slope Calculation in SewerCad

Question

Hi, 
 I have tried to run a 20 pipe layout imported from AutoCAD entered data, gave the Extreme flow calculation coefficients as follows: 
 c1= 0.0; c2 = 5.17; c3 = 0.0; e1 = 0.0 ; e2 = 0.11 ; m1 0.0 ; m2 = 0.001 and population unit in equation = Residents. = 18 
 For the Flow I get 0.36 l/s where as a simple hand calculation would yield me a flow of 0.58 l/s 
 What can be the problem. 
 Also, the program appears to be taking the pipe in and pipe out invert levels as those of manhole center levels and calculate the slopes using the center to center distances of manholes. 
 Shall be grateful for an answer. 
 Aloy

Jesse Dringoli · Accepted Answer

Aloy, 
 
Regarding the extreme flow factor question: 
 
Unit count = 18 
Base flow = 18 * 350 L/d = 0.0729 L/s 
 
EFF = 0 + ( (5.860 + (0*P)^1) / (0+(0.001*P)^0.2 ) ) 
EFF = 5.860 / ((0.001 * P)^0.2) 
EFF = 5.860 / 0.44777 
EFF = 13.087 
 
13.087 is greater than the Cutoff Value of 5.0 (set in the Extreme Flows dialog) So, 
 
EFF = 5.0 
 
Total load = EFF * base flow 
Total load = 5.0 * 0.0729 L/s = 0.36 L/s 
 
0.36 L/s is what you see as the total load from the manhole.

Sushma Choure · Answer

Hello Aloy, 
 The reason why you are not able to get the results is, you haven't specified any size of the conduit from the conduit catalog. 
 After you have selected, conduit type as conduit catalog, you need to pick one size from by selecting the catalog class, later software will design the size as required based on the flow and provided sizes in the conduit catalog.. 
 
 You can define the size of conduit from properties, flex table or physical alternatives. 
 Also I see that you have defined the unit sanitary load but there is no loading unit count, so there will be no flow through the pipes.

Sushma Choure · Answer

Hello Aloy, 
 Looks like we missed this thread, do you still need assistance with this? 
 % of pipe full is right as mentioned in the sewer modeling book, however that also depends upon the criteria what the council of your refion is accepting the designs for. So you should set that % as per your criteria. 
 For V8i, you can go to Componenets>Default Design Constraints>Gravity Pipe>Extended Design>Is Part Full Design? 
 Here you can specify the % of conduit full for the design.

Jesse Dringoli · Answer

Regarding your question on center to center distance - yes, that is currently how scale lengths and slopes are calculated. See more here: 
 
 communities.bentley.com/.../22291.center-to-center-vs-wall-to-wall-length-and-slope-calculations

Sushma Choure · Answer

Hello Aloy, Thanks for uploading the model files. As for the pipe invert levels and slope, you have set up "Set Invert to Start?" & "Set invert to Stop" for conduits to TRUE, meaning pipe inverts will be equal to that of the manholes, so the slope is calculated based on the manhole invert levels. You should set up a conduit catalog, allow software to select the pipe sizes, set "Set Invert to Start?" & "Set invert to Stop" to FALSE which will consider the drop structure allowing you to have drops as required.

Sushma Choure · Answer

Hello Aloy, 
 
Did you create the items in the conduit catalog or imported from engineering library? 
Please make sure that you are selecting the pipes which are available in the conduit catalog for design. 
If this doesn't help then please, upload the revised model files.