We are attempting to simulate dry weather flows and pollutant loads with the sanitary layer of Visual Hydro. When we run the simulation without water quality the results seem fine.

Once we add the water quality parameters the computed flows are almost zero.

As we review the output file, we found something very strange!!

We had input T_ADWF as 262 cfs, and it was reported corrected in the ASCII output data group O1. However, ADWF was stated at the bottom of the labeled OUTPUT OF SUBAREA CALCULATIONS as follows;

"Comparison of measured (adwf) and calculated (smtdwf) Total sewage flow:

ADWF = 0.499 CFS. SMTDWF = 5.483E+02 CFS.

Dry=weather flow quantity (and quality load rate) is multiplied by a
correction factor, adwf/smtdwf = 9.101E-04 at each inlet."

(Note this text did not appear when the model was run without the water quality parameters)

The "measured (adwf)" is not the value we input as ADWF=262 CFS, but the sewage flow listed for the last manhole in the table following this text:

###########################################################
#         DRY WEATHER FLOW GENERATION SUBAREA DATA        #
 #  Land Use = 1 is Single Family Residential              #
 #  Land Use = 2 is Multi-Family Residential               #
 #  Land Use = 3 is Commercial                             #
 #  Land Use = 4 is Industrial  Land Use = 5 is Parkland   #
 #  Dry Weather Sewer Flow Method = 1 is Sewage Flow       #
 #  Dry Weather Sewer Flow Method = 2 is Winter Water Use  #
 #  Dry Weather Sewer Flow Method = 3 is Estimated         #
 #  Water Unit = 0 means 1000 gallons/month                #
 #  Water Unit = 1 means 1000 cubic feet/month             #
 #  Note: The process flow concentrations are not listed   #
 #        in the output file after 8/27/97                 #
###########################################################

We believe that the dry flow is multiplied by this incorrect correction factor resulting in a very small flow. Is this correct or are we doing something wrong? One would expect that adding water quality parameters should not have affected the way flows were calculated.

Do you have any comment on this?

Jee and Frank,

The total population that you entered in the total study area dialog was 200000. This population is in units of 1000. Therefore you had over 200 million as the total population. On the level of an individual node you had the correct population density and area thus forcing the model to overcorrect for the small population per node compared to the overall large population.

It looks like you want to use the normal "filth" option in Transport, but this often has unforeseen consequences based on the data you have entered compared to Baltimore in the 1950s. I would suggest that you use the DWF=1 or DWF=3 options in Visual Hydro or XP-SWMM and simply use the average sewage flow and average sewage water quality concentration that you have entered at the transport node. The options DWF=1 and DWF=3 are entered in the SWMM configuration dialog.

I have also had problems with the ADWF computations in XP-SWMM's sanitary layer. I was hoping that Visual Hydro would have fixed them. My problems related to incorrect processing of Transport Block FILTH subroutine input parameters for computing dry weather flow quantity. I then found out that XP-SWMM and VH DWF routines do not process all the FILTH parameters. Whey then the input dialogues for them? With the advent of GIS and public domain census data we now have an opportunity to estimate DWF quantity and quality internally rather than input a pre-estimated or measured flow value. It will be helpful if the full FILTH capability is implemented.