QUAL2K is a 1-dimensional, steady state, instream water quality model for well mixed channels (laterally and vertically). Constituents modeled include: ammonia, nitrate, organic and inorganic phosphorous, algae, sediment, pH and pathogens. QUAL2K was developed by Dr. Steve Chapra and his grad students at Tufts University.
To model a WEAP constituent using QUAL2K, choose "Modeled in QUAL2K" in the Calculate By column. If you want to model any constituents in QUAL2K, you must also model water temperature in QUAL2K. QUAL2K will calculate water temperature for each river reach based on WEAP climate data (air temperature, dew point, wind speed, and cloud cover and shade fractions) input in the Data view (under the Climate tab for the reach). For each constituent that will be modeled in QUAL2K, choose the corresponding QUAL2K constituent in the Link to QUAL2K Constituent column. Note: you can choose to model just a subset of your constituents in QUAL2K, with the others modeled in WEAP.
QUAL2K has many parameters and options, too many to include in WEAP. Therefore, you will need to first create a QUAL2K data file (.q2k) with the appropriate parameters. Use the Excel file QUAL2K.xls in the WEAP directory to create and edit QUAL2K data files. Put that .q2k input file into the WEAP area's subdirectory and select it using the .q2k data file drop down in the lower left of the Water Quality Constituents window. Alternatively, choose < Copy file from another directory > from the drop down to copy the .q2k file from another directory.
If the QUAL2K data file (.q2k) includes more than one river, you will need to match the rivers in the QUAL2K data file with those in WEAP. Click the "Link WEAP Rivers to QUAL2K Rivers" button below the .q2k data file drop down (the button will only appear if the .q2k file has multiple rivers). Note: you do not need to model all WEAP rivers in QUAL2K -- you may choose to model some and not others. However, every river in the QUAL2K file (.q2k) must be linked to a river in WEAP, and those WEAP rivers must have Model Water Quality? turned on, and all WEAP rivers not linked to QUAL2K must have water quality modeling turned off.
When WEAP calculates, it will read in the specified .q2k data file, add to it the data specified in WEAP (headflows, point and diffuse sources of water and pollution, climate data), write the new .q2k file and run QUAL2K. Because QUAL2K provides for more detailed water quality modeling than is available in WEAP, you may want to take the .q2k file created by WEAP and examine, modify and run it yourself in the QUAL2K Excel interface. To do so, check the Save every .q2k file created (for each time step) checkbox, and specify Where to save each .q2k file. After WEAP calculates, you will find a new .q2k file in this directory for every scenario and time step (e.g., for a monthly time step over 20 years for 4 scenarios, there will be 960 .q2k files created). Each .q2k file occupies about 20K of disk space. You may then load any of these files yourself in QUAL2K and change data (e.g., add diurnal variation to climate data) and view results in the many graphs available in the QUAL2K Excel interface.
See QUAL2K Overview for more information about QUAL2K, and Running QUAL2K in the Calculation Algorithms section for more information about the linkage from WEAP.