You are here

Home › Forums › W2 Forum › Water Quality

Tributary Inflow Concentration - Incorrect

Tue, 07/26/2016 - 1:09pm — Baljit
I am trying to model part of the Ohio River for a conservative tracer (only). My current study area consists of 49 segments and 17 layers. I have a point source load entering at segment 38, currently included in the model as a tributary. There is no external source of tracer upstream of segment 38. However the model gives output with high concentration of tracer upstream of segment 38 which is not right. I did a sensitivity analysis by turning the tributary concentration control OFF and just showing the background tracer. The results comply by the input data. What are the factors to be taken into consideration while adding point source loadings? Manual states: “If the current upstream segment [CUS] number is greater than the segment the tributary enters, then the tributary inflows are added into the current upstream segment to maintain the waterbody water balance”. How to locate the current upstream segment? The manual also states,” The current upstream segment [CUS] is calculated by the model and may vary over time to meet restrictions imposed by the solution scheme”. I would also like to mention that I am getting negative flow values for all of the segments in the output file (tsr.opt). What could cause negative flows? I would really appreciate if I can get some assistance on my query. I am a fairly new user (3 weeks) and none of my colleagues at work have used this model before.
Forums: 
Water Quality
Wed, 07/27/2016 - 8:16am — Amir

Hi Baljit. Did you define a water level control structure that causes the reverse flow? such as spillway, gate or weir.
Wed, 07/27/2016 - 8:24am — Baljit

Hi Amir. I don't have any structures defined, the NSTR value is set to 0.
Wed, 07/27/2016 - 2:55pm — Baljit

Hi Amir, I selected the Snapshot File Output and printed the snp.opt file. As per the output file, the tributary inflow concentration for the Tracer (included in mg/L in the input file) is shown as Water Age in days. So the model is treating Age or Resident Time as the generic constituent instead of Tracer. In all of the constituent control cards, I do not have AGE constituent ‘ON’. I have only one constituent (generic constituent) TRACER that is ON. Could you please provide any suggestions where I might be going wrong? What parameters I need to check? I have checked the control file and formatted the input file several times. I would really appreciate your assistance. Thanks
Thu, 07/28/2016 - 8:32am — Amir

  • So are the kinetic parameters set to zero?
  • Manual: For a tracer, all of the kinetic parameters should be set to zero.
  • For residence time (age), the 0-order decay rate should be set to -1.0.
  • .
  • So please check if the 0-order decay rate (CG0DK) is zero.
  • .
  • GENERIC .. CGQ10 . CG0DK . CG1DK . . CGS
  • TRACER . .. . 0.000 .. 0.000 . . 0.000 . 0.000
  • AGE . . . . . . 0.000 . -1.000 . . 0.000 . 0.000
  • Coliform . . . 1.040 . . 0.000 . . 1.400 . 0.000
If all the parameters are zero and still the model treats the input as age, then define three groups as listed above instead. Maybe (again maybe) the model consider the genetic constituent as "Age" when only one groups is defined (very improbable).
Thu, 07/28/2016 - 12:38pm — Baljit

Thank you so much for responding to my query. I had the kinetic parameters set right, however the order of generic constituents listed in the graph.npt file was not matching with the control file. After changing the sequence, I got the output for tracer in g/m3. However, I am still having issues with reverse flow and higher concentration of tracer upstream of segment where tributary enters. Could you please provide any insight on it? Once again, thank you for your help.
Thu, 07/28/2016 - 3:04pm — Amir

You are very welcome Baljit. Regarding reverse flow, the only issues that come to my mind are:
  1. A water level control structure such as spillway, gate or weir
  2. External downstream head
  3. Incorrect bathymetry. Mainly in reservoirs, when the deeper parts defined at upstream
  4. Negative slope for rivers. When we gives negative values for river slope in the branch definition section
  5. It can also be due to rapid changes to flow (decreasing).
I suggest that you do some tests : for example increase the river slope and see if you still have the reverse flow. check the initial water level in the bth file. Is your DHS=0? How is the inflow compared with the outflow?
Tue, 08/02/2016 - 10:20am — Baljit

Hi Amir, Thank you so much for your suggestions. I made the following changes/checks to my control file, bathymetry file and constituent concentration file. 1. Increased slope from 0.00006 to 0.0001 2. Updated the EBOT and ELWS parameters as per the new slope 3. Checked for any outlet structures, NSTR = 0; DHS = 0 4. Checked the tributary constituent concentration file to see the format is correct 5. Checked the order of constituents matches in the Active Constituent Card and Graph Input file 6. Since I have non-stratified flow, I assumed the vertical eddy viscosity coefficient (AZMAX) = 0 7. The outflow is always zero for all segments at any given time of the year, whereas the inflow varies between negative and positive values. I would really appreciate if you could provide some assistance on resolving this issue. Thanks, Baljit
Thu, 08/04/2016 - 10:44am — Amir

Hi Baljit. I am out of idea now. Did you change the SLOPEC as well. The SLOPE is for defining the bathymetry and the SLOPEC (with exrta C) is used in flow equations. 2- How is the outflow defined? If these are not working you can send me the npt files. Maybe I find something in those. my email address is amir.sadeghian@usask.ca . Amir