SWATMOD-Prep: Interface for Preparing SWAT- MODFLOW Simulations

Transcription

1 SWATMOD-Prep: Interface for Preparing SWAT- MODFLOW Simulations Written: June 2016 User s Manual Developers Hendrik Rathjens, Purdue University Katrin Bieger, Blackland Research & Extension Center, Texas A&M AgriLife Ryan Bailey, Colorado State University (rtbailey@engr.colostate.edu) Overview of SWATMOD-Prep SWATMOD-Prep is a graphical user interface developed to create a fully linked SWAT-MODFLOW model based on an existing SWAT (version 2012) model that has been created with the ArcSWAT interface. The user defines a finite difference grid for a MODFLOW model, which is then linked with the HRUs and subbasins of the SWAT model through geoprocessing routines. Currently the software is available only for Windows. Mandatory requirements: - SWAT model version Existing ArcSWAT project with zero threshold HRUs Purpose of this User s Manual The purpose of this user s manual is to describe the process of installing and using SWATMOD-Prep on any personal computer or laptop. The manual also describes the input data that need to be provided by the user and the output that might be helpful interpreting model results. Internal input/output dependencies are not listed. Getting Started Download the executable Setup_SWAT-MODFLOW-Interface and run it by double-clicking on the file. This will bring up the Interface Setup Wizard. Follow the prompts to install SWATMOD-Prep onto your computer. The files and libraries required to run SWATMOD-Prep are now contained in the folder SWAT-MODFLOW Interface in the location you specified in the Setup Wizard. The main folder also contains the SWAT-MODFLOW model executable (SWAT-MODLFOW.exe). A desktop icon also is created. Use this icon to run SWATMOD-Prep. Layout of Interface SWATMOD-Prep consists of 4 tabs: - Spatial Setup Loading SWAT model, specifying grid cell size, performing linking operations - MODFLOW Loading required data to construct MODFLOW model - RT3D Loading required data to construct RT3D model (optional) - Simulation Specifying timing information, output options, and running the simulation 1

2 Example Dataset An example dataset for the Little River Experimental Watershed (LREW), Georgia, accompanies this tutorial to demonstrate the use of SWATMOD-Prep to construct a linked SWAT-MODFLOW model. To access the LREW datasets, unzip the file Example_Dataset.zip that accompanies this tutorial. The following folders will be made accessible: - modflow_parm_grids input rasters for MODFLOW model of the LREW - modflow_table observation grids cells for the MODFLOW model of the LREW - rt3d_parm_grids input raster (porosity) for the RT3D model of the LREW - swat_shapes shape files (HRU, River Network, Sub-basins) for the SWAT model of the LREW - SWATmodel input files for the SWAT model of the LREW The following tutorial provides step-by-step instructions for each of the 4 tabs of the interface. Generic instructions are provided with screen shots of the tabs and buttons, followed by instructions for loading LREW datasets. 2

3 1. Spatial Setup tab The first tab of the interface provides the basic linkage between the existing SWAT model and a new MODFLOW model. The interface is shown below, with the steps highlighted within the figure: Step 1.1 Step 1.2 Step 1.3 Step 1.4 Step 1.5 Step 1.6 Step 1.7 Step Specify Path to TxtInOut Folder Define the SWAT-MODFLOW project folder by specifying the path to the SWAT TxtInOut folder associated with the existing SWAT model. The TxtInOut folder usually is located in the ArcSWAT project directory in the folder \Scenarios. However, any folder containing the SWAT ASCII input files can be used. It is recommended to make a back-up of the original SWAT model. 3

4 The interface saves all intermediate steps and the user can go back to the SWAT- MODFLOW project at any time to continue the project or change parameter values. File name Location Description interface_modflow_db.json TxtInOut folder Interface database for internal use MODFLOW_GIS Parent of TxtInOut folder Folder for saving intermediate MODFLOW GIS files LREW: Specify the path to the TxtInOut folder, located in the SWATmodel folder. 1.2 Load SWAT DEM, Sub-basin, HRU and River Shapefiles Specify the paths to the sub-basin, HRU (no thresholds) and river network shape files that were created by ArcSWAT. They are usually located in the ArcSWAT project folder in the subfolder Watershed\Shapes and named subs1.shp, hru1.shp, and riv1.shp. If multiple shape files have been created during the initial ArcSWAT setup, the number in the filename might be different. Make sure to select the files corresponding to the TxtInOut folder selected in Step 1.1. The interface saves a copy of each shape file in the MODFLOW_GIS folder once all file paths have been provided. Input files: Information and file type Sub-basins (subs<number>.shp) HRUs (hru<number>.shp) Stream network (riv<number>.shp) Description ArcSWAT sub-basin shape file ArcSWAT HRU shape file with zero thresholds ArcSWAT River network shape file File name Location Description swat_sub.shp MODFLOW_GIS Copy of ArcSWAT subbasin shapes (multiple files) swat_hru.shp MODFLOW_GIS Copy of ArcSWAT hru shapes (multiple files) swat_sub.shp MODFLOW_GIS Copy of ArcSWAT river network (multiple files) LREW: Load the subs1.shp, hru1.shp, and riv1.shp shape files, located in the swat_shapes folder. 1.3 Convert to Raster The ArcSWAT shape files need to be converted to a raster format, because in a later step the MODFLOW raster and the spatial SWAT input files need to be overlaid. Ideally, the grid cell dimension in this field should be a divisor of the desired MODFLOW grid cell size. The interface calculates a raster cell size that allows rasterization of the shape files without losing information. The user, however, can adjust this value to make it a divisor of the 4

5 desired MODFLOW grid cell size. If the input cell size is not an integer the interface will convert the input grid cell dimension to the nearest integer. Later, the interface will resample the spatial input files to the greatest common divisor of the grid cell dimensions in this field and the desired MODFLOW resolution. As a compromise between computation time, memory requirements, and spatial accuracy, it is recommended to keep the suggested grid cell dimension value and to adjust the MODFLOW grid cell size accordingly. For example, if 30 m is the suggested grid cell size and 200 m is the desired MODFLOW grid cell size, we suggest keeping the 30 m grid cell size and adjusting the MODFLOW grid cell size to 210 m. swat_subo.tif MODFLOW_GIS Subbasin raster in given resolution swat_hruo.tif MODFLOW_GIS HRU raster in given resolution swat_rivo.tif MODFLOW_GIS Stream network raster in given resolution LREW: Keep the recommended value of 30 m in the Grid Cell Dimensions edit field, and press the Convert to Raster button. 1.4 Set up MODFLOW Grid The MODFLOW grid is created during this step. As outlined in Step 1.3, it is strongly recommended to choose a MODFLOW resolution that is a multiple of the grid cell dimension selected for rasterizing the ArcSWAT shape files. mf_grid_overlay.tif MODFLOW_GIS MODFLOW raster in overlay resolution (greatest common divisor of ArcSWAT and MODFLOW grid cell dimensions). The grid value corresponds to the MODFLOW cell ID. mf_grid.shp MODFLOW_GIS Shape of MODFLOW raster (multiple files). The MODFLOW ID of each cell is provided in the attribute table. mf_grid.tif MODFLOW_GIS MODFLOW raster in MODFLOW resolution. The grid value corresponds to the MODFLOW ID. swat_sub.tif MODFLOW_GIS SWAT subbasin raster in overlay resolution. The grid value corresponds to the subbasin number. swat_hru.tif MODFLOW_GIS SWAT HRU raster in overlay resolution. The grid value corresponds to the HRU number. swat_riv.tif MODFLOW_GIS SWAT stream network raster 5

6 in overlay resolution. The grid value corresponds to the channel number. mf_rivercells.shp MODFLOW_GIS MODFLOW stream network. Each MODFLOW cell that intersects a SWAT river cell is defined as a MODFLOW River cell. The MODFLOW cell ID is provided in the attribute table. LREW: Enter 210 into the Grid Cell Dimensions edit field, and press the Create Grid button. With the existing SWAT model loaded and the MODFLOW grid created, the SWAT model and the grid can now be linked and the necessary SWAT-MODFLOW input files can be written. This is described in steps Disaggregate HRUs MODFLOW is a grid based distributed model and SWAT HRUs are lumped areas which do not have a geographic position within a sub-basin. To link SWAT and MODFLOW, the HRUs need to be converted to Disaggregated HRUs (DHRUs), with each separate polygon becoming an HRU. mf_dhru.tif MODFLOW_GIS DHRU raster in overlay resolution. The grid value corresponds to the DHRU ID. hru_dhru TxtInOut Linkage table between HRUs, DHRUs and sub-basins. LREW: Press the Disaggregate HRUs button. 1.6 Intersect MODFLOW Grid and DHRUs The linkage between DHRUs and MODFLOW grid cells is provided during this step. mf_grid_overlay_active.tif MODFLOW_GIS MODFLOW raster in overlay resolution showing active grid cells. The grid value corresponds to the MODFLOW cell ID. mf_grid_active.tif MODFLOW_GIS MODFLOW raster in MODFLOW resolution showing active grid cells. The grid value corresponds to the MODFLOW cell ID. mf_grid_active.shp MODFLOW_GIS Shape of the active MODFLOW raster (multiple 6

7 files). The MODFLOW cell ID and the corresponding row and column are provided in the attribute table. grid_dhru TxtInOut Linkage between MODFLOW grid cells and DHRUs. dhru_grid TxtInOut Linkage between DHRUs and MODFLOW grid cells. LREW: Press the Intersect MODFLOW Grid and DHRUs button. 1.7 Identify river cells The linkage between MODFLOW river cells and sub-basins is provided during this step. river_grid TxtInOut Linkage between MODFLOW river cells and sub-basins. LREW: Press the Identify River Cells button. 1.8 Write SWAT-MODFLOW linkage files During this step the linkage tables created in Steps 1.5 to 1.7 are used to create SWAT- MODFLOW specific mapping files in an intermediate format. swatmf_dhru2hru.txt TxtInOut DHRU to HRU mapping file. swatmf_dhru2grid.txt TxtInOut DHRU to MODFLOW-Grid mapping file. swatmf_grid2dhru.txt TxtInOut MODFLOW-Grid to DHRU mapping file. swatmf_river2grid.txt TxtInOut MODFLOW-River-Grid to MODFLOW-Grid mapping file. LREW: Press the Write SWAT-MODFLOW Linkage Files button. 7

8 2. MODFLOW tab This tab and the associated loaded data will create a single-layer MODFLOW model for the study watershed. Required data to construct a MODFLOW model include aquifer characteristics, streambed conductivity, and initial values of groundwater hydraulic head. For the MODFLOW input files, each grid cell needs a value of each parameter. Within the interface, most parameters can be provided as a single value, which then is copied to each grid cell, or else as as spatially distributed values. The SWAT- MODFLOW interface requires all spatial input in the GeoTIFF format (*.tif). Any GIS software can be used to convert the spatial input from shape files or other raster formats to the GeoTIFF format. Make sure that the GeoTIFF file is projected. The interface will: 1) re-project the GeoTIFF to the projection given by the ArcSWAT spatial files (subbasin, HRU, and river shape files, see Step 1.2); 2) resample it to the resolution and extent of the MODFLOW grid (see Step 1.4) using bilinear interpolation; 3) interpolate data gaps by assigning the mode of the data gap s surrounding; and 4) clip it to the active MODFLOW grid cells (see Step 1.6). If a different resampling or interpolation technique is preferred, the steps outlined above can be done manually using any GIS software. The interface will keep the data as it is if no resampling, re-projecting, or clipping is necessary. Once all information has been provided, the Write MODFLOW Input Files button becomes active (see Step 2.9). 2.1 Load DEM MODFLOW needs the ground surface elevation for the grid cell (this will be used as the top of the layer). Set the path to the DEM that has been used during the initial ArcSWAT setup. Input files: Information and file type DEM (*.tif) Description Projected digital elevation model used in ArcSWAT setup. mf_dem.tif MODFLOW_GIS Ground elevation in MODFLOW resolution. LREW: Load the groundelevation30.tif file located in the modflow_parm_grids folder. 2.2 Aquifer Thickness Provide either a single value for the entire watershed or specify the path to a raster representing the aquifer thickness in the watershed. Optional input files: Information and file type Aquifer Thickness (*.tif) Folder Aquifer Thickness in meter. Optional new files: mf_aqu.tif MODFLOW_GIS Aquifer Thickness in MODFLOW resolution. LREW: Load the aquthick.tif file located in the modflow_parm_grids folder. 8

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10 2.3 Hydraulic Conductivity Provide either a single value for the entire watershed or specify the path to a raster representing the hydraulic conductivity of the aquifer in the watershed. Optional input files: Information and file type Hydraulic conductivity (*.tif) Description Hydraulic conductivity in meters per day. Optional new files: mf_hyc.tif MODFLOW_GIS Hydraulic conductivity in MODFLOW resolution. LREW: Load the hydcon.tif file located in the modflow_parm_grids folder. 2.4 Ratio of horizontal K to vertical K Provide a single value for the entire watershed. LREW: Enter 1.0 in the Ratio of K H to K V edit field. 2.5 Specific Storage Provide either a single value for the entire watershed or specify the path to a raster representing the specific storage of the aquifer in the watershed. Optional input files: Information and file type Specific storage (*.tif) Description Specific storage in meter per day. Optional new files: mf_sps.tif MODFLOW_GIS Specific storage in MODFLOW resolution. LREW: Load the specstor.tif file located in the modflow_parm_grids folder. 2.6 Specific yield Provide either a single value for the entire watershed or specify the path to a raster representing the specific yield of the aquifer in the watershed. Optional input files: Information and file type Specific yield (*.tif) Description Specific yield (dimension less). Optional new files: mf_spy.tif MODFLOW_GIS Specific yield in MODFLOW resolution. LREW: Load the specyield.tif file located in the modflow_parm_grids folder. 10

11 2.7 Hydraulic conductivity of river bed material Provide a single river bed hydraulic conductivity value for the entire watershed in meter per day. LREW: Enter 1.0 in the Hydraulic Conductivity of River Bed Material edit field. 2.8 Initial hydraulic head Provide either a single value for the entire watershed or specify the path to a raster representing the initial hydraulic head of the aquifer in the watershed. If a single value is provided, it will be treated as the depth to the water table, and the initial head for each grid cell will be calculated by subtracting this value from the cell s ground surface elevation. Optional input files: Information and file type Initial hydraulic head (*.tif) Description Initial hydraulic head in meters. Optional new files: mf_ihh.tif MODFLOW_GIS Initial hydraulic head in MODFLOW resolution. LREW: Select Single Value and enter 2.0 in the edit field. The initial hydraulic head thus will be 2 m below the ground surface for each grid cell. 2.9 Write MODFLOW input files During this step the aquifer parameters and geo-spatial information are converted into intermediate MODFLOW input. general_information TxtInOut General information required by MODFLOW in an intermediate format (grid cell dimensions, number of days in simulation, initial hydraulic head, watershed boundary). aquifer_thickness TxtInOut MODFLOW aquifer thickness input file in an intermediate format. aquifer_parameters TxtInOut MODFLOW aquifer parameter input file (hydraulic conductivity, ratio of horizontal K to vertical K, specific storage, specific yield) in an intermediate format. ground_elevation TxtInOut SWAT-MODFLOW ground elevation input file (resampled DEM) in an intermediate format. river_cells TxtInOut MODFLOW river cell input file (hydraulic conductivity of river bed material, stream 11

12 length) in an intermediate format. LREW: Press the Write MODFLOW Information button. All intermediate files for MODFLOW will be written. Note that the actual MODFLOW input files as required by the MODFLOW model code are not written until the Run Simulation button is pressed on the Simulation tab (see Step 4.7). 12

13 3. RT3D tab SWAT-MODFLOW includes an optional linkage to RT3D (Reactive Transport in 3 Dimensions), which simulates the reactive transport of solutes through the aquifer system. Currently, only nitrate is included in the transport module. Other solutes can be included in future versions of the interface. Inside the SWAT-MODFLOW code, RT3D is called as a subroutine by MODFLOW. RT3D uses the same finite difference grid as MODFLOW. The RT3D module requires several parameters representing the aquifer characteristics that affect solute transport, including porosity, longitudinal dispersivity, ratio of transverse to longitudinal dispersivity, and first-order denitrification rate constant. For now, only porosity can be specified as spatially-variable (i.e. a value for each grid cell). In the future, the spatial option can be extended to the other parameters based on user demand. The SWAT-MODFLOW interface requires all spatial input in the GeoTIFF format (*.tif). Any GIS software can be used to convert the spatial input from shape files or other raster formats to the GeoTIFF format (see Section 2). 13

14 3.1 Select RT3D option Write RT3D Input Files Usage of RT3D in the SWAT-MODFLOW simulation is optional. Leave the box unchecked and move on to the Simulation tab if simulating the reactive transport of nitrate through the aquifer system is not needed. Check the box if using RT3D is desired. LREW: If groundwater nitrate transport is desired, check the Write RT3D Input Files box. We recommend not using this option until a SWAT-MODFLOW simulation has already been run. This will help the user become familiar with the SWAT-MODFLOW inputs and outputs before simulating groundwater solute transport. 3.2 Porosity Provide either a single value for the entire watershed or specify the path to a raster representing porosity of the aquifer in the watershed. Optional input files: Information and file type Porosity (*.tif) Description Porosity (dimension less). Optional new files: rt_porosity.tif MODFLOW_GIS Porosity MODFLOW resolution. LREW: Load the Porosity.tif file located in the rt3d_parm_grids folder. 3.3 Longitudinal Dispersivity Provide a single longitudinal dispersivity value in meter for the aquifer. LREW: Enter 2.0 in the Longitudinal Dispersivity edit field. 3.4 Ratio of Transverse to Longitudinal Dispersivity Provide a single ratio of transverse to longitudinal dispersivity for the aquifer (dimension less). LREW: Enter 0.1 in the Ratio of Transverse to Longitudinal Dispersivity edit field. 3.5 Denitrification Rate Constant Provide a single value of the denitrification rate constant per year for the aquifer. LREW: Enter 0.05 in the Denitrification Rate Constant edit field. 3.6 Write RT3D Input files (Write RT3D Information button) Aquifer parameters and geo-spatial information are converted into an intermediate SWAT- MODFLOW format. 14

15 rt3d_parameters TxtInOut General information and parameters required by the RT3D module in an intermediate format (output frequency, porosity, longitudinal dispersivity, ratio of transverse to longitudinal dispersivity, denitrification rate constant). LREW: Press the Write RT3D Information button. All intermediate files for RT3D will be written. Note that the actual RT3D input files as required by the RT3D model code are not written until the Run Simulation button is pressed on the Simulation tab (see Step 4.7). 15

16 4. Simulation tab General SWAT-MODFLOW simulation settings such as simulation period and output specifications can be defined in the Simulation Tab. Once all information needed has been provided, the Run Simulation button becomes active and the user can start the SWAT-MODFLOW simulation (see Step 4.7). 16

17 4.1 Period of Simulation Define the simulation period by specifying a starting and ending date. The interface reads in the information from the file.cio and provides the dates defined during the initial ArcSWAT setup. LREW: Leave the default values in the Starting Date and Ending Date edit fields. 4.2 SWAT Printout Settings Define the warm-up period (NYSKIP, i.e. no output is printed during the first NYSKIP years) and specify the SWAT output time step (daily, monthly or yearly). The interface reads the information from the file.cio and provides the NYSKIP and the output time step defined during the initial ArcSWAT setup. LREW: Enter 5 in the NYSKIP edit field, and set the Time Step to Daily. 4.3 Frequency of MODFLOW Runs Define the MODFLOW time step. LREW: Enter 1 in the Frequency of MODFLOW Runs edit field. MODFLOW will thus be called for each daily time step. 4.4 SWAT-MODFLOW Output I This step is optional. Specify the path to a csv-formatted (coma delimited) table containing the row, column and layer of each MODFLOW grid cell for which groundwater hydraulic head is to be output at each time step. The file mf_grid_active.shp (see Step 1.6) can be used to find MODFLOW row and columns for locations which are of interest to the user. Optional input files: Information and file type Table of observation cells (*csv) Description Table of observation cells in a coma delimited format. The first line is reserved for the header. Information that needs to be provided: row (first column), column (second column), and layer of the cell (third column). Optional new files: observation_cells TxtInOut Table of observation cells. LREW: Load the observation_cells.csv file located in the modflow_table folder. This file lists 9 grid cells for which daily output (i.e. groundwater hydraulic head) is desired. 4.5 SWAT-MODFLOW Output II SWAT-MODFLOW provides several output options. Check the boxes for the desired output. - Deep Percolation for each SWAT HRU [mm] - Recharge for each MODFLOW Grid Cell [m³/day] - Channel Depth for each SWAT Subbasin [m] - River Stage for each MODFLOW River Cell [m] 17

18 - Groundwater/Surface Water Exchange for each MODFLOW River Cell [m³/day] - Groundwater/Surface Water Exchange for each SWAT Subbasin [m³/day] LREW: Check each box (explanations of the output data for each of these options are presented at the end of this tutorial). 4.6 RT3D option and RT3D output frequency These options are available if the RT3D option has been selected on the RT3D tab. RT3D will output cell-by-cell groundwater nitrate concentration according to the value entered in the RT3D Output Frequency edit field. LREW: If the RT3D option has been selected, set the desired frequency. If cell-by-cell concentration is desired every 30 days, then enter 30 in the edit field. 4.7 Run Simulation During this step: (1) Some of the intermediate input files are updated based on information provided in the Simulation Tab; (2) Input in the final SWAT-MODFLOW format is created based on the intermediate input files (see Sections 1 to 3); and (3) The SWAT-MODFLOW model executable is called and the simulation begins running. Updated input files: File Folder Description file.cio TxtInOut Simulation time and print out settings are updated in SWAT s master watershed file. general_information TxtInOut The number of simulation days is updated. See step 2.9 for detailed information. rt3d_parameters TxtInOut The RT3D output frequency is updated. See Step 3.6 for detailed information. MODFLOW input files: File / folder name(s) Folder Description modflow.obs, modflow.mfn, modflow.bas, modflow.dis, modflow.lmt, modflow.nwt, modflow.rch, modflow.oc, modflow.riv, modflow.upw TxtInOut MODFLOW input files. Detailed information about each file can be found in the MODFLOW manual. MODFLOW output files: File / folder name(s) Folder Description modflow.hed, TxtInOut Hydraulic head output file for MODFLOW. Detailed information about each file can be found in the MODFLOW manual. swatmf_out_swat_recharge, swatmf_out_mf_recharge, swatmf_out_swat_channel, swatmf_out_mf_riverstage, TxtInOut 18 Optional SWAT-MODFLOW output depending on the options selected in Step 4.5.

19 swatmf_out_mf_gwsw, swatmf_out_swat_gwsw RT3D input files: File / folder name(s) Folder Description rt3d.adv, rt3d_filenames, rt3d.btn, rt3d.gcg, rt3d.dsp, rt3d.ssm, rt3d.rct TxtInOut RT3D input files. Detailed information about each file can be found in the RT3D manual. RT3D output files and folders: File / folder name(s) Folder Description rt3d_no3grid, rt3d_averages TxtInOut Spatial RT3D NO 3 output and annual RT3D averages for each grid cell. RT3Dout TxtInOut/ rt_output General RT3D output file. CONCNO3, XZNO3 TxtInOut/ rt_output/1concentration RT3D concentration output files. SSMASS_NO3, TxtInOut/ rt_output/2ssmass RT3D mass output files. SSMASS_CUMUL_NO3 OBSNO3 TxtInOut/ rt_output/3observations RT3D output at observation points, currently for cell at row 1 and column 1. LCH_NO3 TxtInOut/ rt_output/6leach RT3D leaching output file. TxtInOut/ rt_output/7mass Empty folder 19

20 5. Using Output Files to View Model Results The SWAT-MODFLOW simulation will produce several primary output files and, if selected in the Simulation tab, up to 6 additional output files. These are in addition to the typical SWAT output files used in displaying water budgets, stream discharge, etc. modflow.hed This file contains the calculated groundwater hydraulic head for each MODFLOW grid cell, for each specified time step of the simulation (the time steps at which values will be written are specified in the modflow.oc file). For each output time, there is a header line (time step, stress period), followed by the hydraulic head values written by row and column. No-data values (i.e. cells outside of the watershed boundary) are represented by swatmf_out_mf_obs Created only if option is selected in the Simulation tab. This file contains the groundwater hydraulic head of the observation cells, for each MODFLOW time step. For each time step, the head values for each observation cell are printed on a single line, in the same order as the cells are listed in the.csv file loaded in the Simulation tab. swatmf_out_swat_recharge Created only if option is selected in the Simulation tab. This file contains the depth (mm) of deep percolation ( = recharge to MODFLOW) calculated for each HRU, for each day of the simulation. Following the header line ( SWAT deep percolation (mm) (for each HRU) ), the deep percolation values for each HRU (beginning with HRU #1) are written for the first day, followed by a blank line, followed by the values for the next day, etc. swatmf_out_mf_recharge Created only if option is selected in the Simulation tab. This file contains the volumetric flow rate of recharge (m 3 /day) of recharge provided to each MODFLOW grid cell, for each day of the simulation. The values are written in a 2D format according to the number of rows and columns in the MODFLOW grid. These values can be displayed as raster datasets in GIS to display the recharge to the water table. swatmf_out_swat_channel Created only if option is selected in the Simulation tab. This file contains the channel depth (m) for each sub-basin channel, for each day of the simulation. For each day, the depths are written on a single line, with the depth for sub-basin #1 in the first column, depth for sub-basin #2 in the second column, etc. up to the last sub-basin. swatmf_out_mf_riverstage Created only if option is selected in the Simulation tab. This file contains the river stage ( = channel depth) (m) for each MODFLOW river cell, for each day of the simulation. These values are obtained from the sub-basin channel depths computed by SWAT. Output from consecutive days is separated by a blank line. 20

21 swatmf_out_swat_gwsw Created only if option is selected in the Simulation tab. This file contains the volumetric exchange rates (m 3 /day) between the stream network and the aquifer for each SWAT sub-basin (numbered consecutively), for each day of the simulation. Positive values signify groundwater flow to the channel, whereas negative values signify stream seepage to the aquifer. Output from consecutive days is separated by a blank line. swatmf_out_mf_gwsw Created only if option is selected in the Simulation tab. This file contains the volumetric exchange rate (m 3 /day) between the stream network and the aquifer for each MODFLOW River cell (numbered consecutively), for each day of the simulation. Negative values signify groundwater flow to the channel (MODFLOW treats the aquifer as the control volume, and water leaving the aquifer is denoted by a negative value), whereas positive values signify stream seepage to the aquifer (i.e. a source to the aquifer). Output from consecutive days is separated by a blank line. rt3d_no3grid Created only if RT3D option is selected in the RT3D tab. This file contains groundwater nitrate concentration for each grid cell, for each day of the simulation. Values are written in a 2D format according to the number of rows and columns in the grid. These values can be displayed as raster datasets in GIS to display spatially-variable nitrate concentration in the aquifer. Output from consecutive days is separated by a blank line. ssmass_no3 Created only if RT3D option is selected in the RT3D tab. This file is located in the rt_output/2ssmass folder. It contains the mass (grams) of nitrate exchanged between the stream network and the aquifer for each MODFLOW River cell (numbered consecutively), for each day of the simulation. Negative values signify nitrate loaded from the aquifer to the stream channel (RT3D treats the aquifer as the control volume, and nitrate mass leaving the aquifer is denoted by a negative value), whereas positive values signify nitrate loaded from the stream to the aquifer (i.e. a source of nitrate to the aquifer). Output from consecutive days is separated by a blank line. 21