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ArcSWAT / ArcGIS 10.1

Example 3

Note: A personal flash drive is required. Create a folder named Ex3 on the flash drive for the

SWAT simulations. Go to the C:\SWAT\ArcSWAT\Databases directory and copy Example1 to

the Ex3 folder on the flash drive.

Getting Started

1. Start ArcMap New Maps Blank Map Ok Customize Extensions check

Spatial Analyst / SWAT Project Manager / SWAT Watershed Delineator

***Make sure to save your files on a flash drive***

Explanation: Create an ArcMap project file using the ArcSWAT extension of ArcGIS

10.1 that will link GIS databases with the ArcSWAT hydrologic model.

Create new SWAT project / Setup working directory / Setup Geodatabases

1. SWAT Project Setup New SWAT Project Save current document? No Project

Setup dialog box appears Project Directory select folder icon connect to folder

navigate to the flash drive Ok select the Ex3 folder

(***single click***) Ok SWAT Project Geodatabase change the name to

Ex3Output.mdb (Note: You name this file anything but it must have a .mdb extension – it will go

in the Project Directory) Raster Storage leave the name RasterStore.mdb (it will go in the

Project Directory) SWAT Parameter Geodatabase leave the default path

G:\Ex3\SWAT2012.mdb Ok wait patiently Project setup is done Ok

Explanation: The Project Directory is where all of the project files will be stored.

Watershed Delineation (Note: You can exit the Watershed Delineation and reopen it at anytime)

1. Watershed Delineator Automatic Watershed Delineation Watershed Delineation box

appears DEM Setup Load from Disk Ok go to

C:\Swat\ArcSWAT\Databases\Example1 Select DEM Add DEM projection setup

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Click on the DEM Properties box appears Check the units for the Z Unit make

sure that the Z Unit in the DEM Properties box is meters Ok

Explanation: The Digital Elevation Model (DEM) grid is added as a GIS layer to the

ArcMap project file.

Focusing on the watershed of interest using a pre-prepared “mask” – Speeds up GIS processing

2. Peg mask Click the folder icon next to the mask box select Load from Disk Ok

select amask Add

Explanation: The mask covers the watershed that you plan to simulate with a little

overlap around the watershed boundaries. The mask is pre-prepared and is added as a

GIS layer to the ArcMap project file. Later examples will show how to manually create a

mask. The mask is used to exclude areas outside of your selected watershed. Therefore

only the data inside of the mask area are utilized in the SWAT simulation thereby

speeding up computer processing time.

Defining the stream network – Use the threshold area method

3. Go to the Stream Definition box peg DEM-based go to the Flow direction and

accumulation box and click on the icon End of DEM grid preprocessing Ok in the

Area box change the value to 1000 Ha (In example 1 we set the threshold to 500. The smaller the

number, the more detailed the stream network generated.) go to the Stream network box

click on the icon End of stream preprocessing Ok

Explanation: The watershed boundaries and the stream network in the watershed is

calculated from the DEM using the flow direction and flow accumulation method. The

locations of the subbasin outlets are also defined. A minimum, maximum and suggested

subbasin areas (in hectares) can be defined.

Defining outlet and inlet definition

4. Go to the Outlet and Inlet Definition box peg Subbasin outlet click the folder icon and

select C:\Swat\ArcSWAT\Databases\Example1\nutrient.dbf Add Ok Ok we will

also add subbasin outlets manually. Click the ADD button Under edit manually Click

the 4 outlet points using the mouse (see the figure below). It shows red dots. after adding 4

points, click the right mouse button and stop editing yes

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In the Outlet and Inlet Definition box Peg inlet of draining watershed click the folder icon

and select C:\Swat\ArcSWAT\Databases\ExInputs\Inlet.dbf Add Ok Ok

In the Outlet and Inlet Definition box Peg point source input click the folder icon

and select C:\Swat\ArcSWAT\Databases\ExInputs\PntSrc.dbf Add Ok Ok

The added 4th outlet and added inlet point are close to each other now. So, we will delete the 4th

outlet peg subbasin outlet click the delete button under Edit manually select 4th

outlet Ok click the right mouse button Stop editing yes

There are 3 manually added outlets, 2 table added outlets, 1 table added inlet and 1 table added

point source.

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Defining the main watershed outlet

4. Go to the Whole watershed outlet(s) box and click on the icon Ok use the mouse

to draw a box around the watershed outlet (note: you may have to zoom-in if outlets are close-

together to make sure the box is drawn around the correct outlet) 1 outlets selected Ok

Explanation: Selecting the watershed outlet will define the boundary of the main

watershed.

Delineate the watershed

5. Go to the Delineate watershed box and click on the icon Watershed delineation is

done Wait patiently Ok

Explanation: After this step the delineated watershed with all subbasins will be added as a

GIS layer to the ArcMap project file.

Calculate the subbasin parameters

6. Go to the calculate subbasin parameters box and click on the icon Wait patiently

Subbasin parameter calculation successfully done Ok

Main watershed outlet

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In this exercise, we will add a reservoir. Click add reservoir button Ok click on the

main watershed outlet click the right mouse button stop editing yes back to the

watershed delineation window Exit

Explanation: This function calculates basic watershed and subbasin characteristics from

the DEM. A Topographic Report can be opened by going to the Watershed Delineator

tab Watershed Reports Topographic Report Ok. Each subbasin is given a

unique ID number.

Defining the Land Use

1. HRU Analysis Land Use / Soils / Slope Definition Land Use Data tab the Land Use

Grid box and click on the open file folder icon peg Load Land Use dataset(s) from disk

Open Is the grid or shapefile projected? Yes highlight the landuse grid file

(C:\Swat\ArcSWAT\Databases\Example1) Select Ok go to the Choose Grid Field box

and from the drop-down menu select Value Ok click the LookUp Table button peg

User Table Ok highlight luc.dbf Select Reclassify Ok

Explanation: The landuse dataset is added as a GIS layer to the ArcMap project file. The

SWAT LandUse Classification Table will be created automatically (see Figure below).

However, in order to fill the 3’rd column (LandUse SWAT) a look-up table (in .txt or

.dbf format) can be imported or the 3’rd column can be manually entered. The look-up

table converts the GIS landuse classification to a classification code recognized by the

SWAT model (RNGE, PAST, URBN, etc).

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Defining the Soil Types

1. Click the Soil Data tab go to the Soils Grid box and click on the open file folder icon

peg Load Soils dataset(s) from disk Open Is the grid or shapefile projected? Yes

highlight the soil grid file Select Ok go to the Choose Grid Field box and from the

drop-down menu select Value Ok go to the Soil Database Options box peg

ArcSWAT STATSGO from the ArcSWAT STATSGO drop-down box select Stmuid

click the LookUp Table button highlight soilc.dbf Select Reclassify Ok

Explanation: The soils dataset is added as a GIS layer to the ArcMap project file. The SWAT

Soil Classification Table will be created automatically (see Figure below). However, in order to

fill the 3’rd column (Stmuid = STATSG (State Soil Geographic database) polygon number,

dominate soil phase) a look-up table (in .txt or .dbf format) can be imported or the 3’rd column

can be manually entered. The look-up table converts the GIS landuse classification to a

classification code recognized by the SWAT model. The soil map grid must be linked to the U.S.

soils database that is provided with the ArcGIS interface or to a customized User Soils database.

Defining Slopes

1. Click the Slope tab peg Multiple Slope go to the Number of Slope Classes box and in

the drop-down menu select 3 go to the Current Slope Class box and in the drop-down menu

select 1 go to the Class Upper Limit (%) box and type-in 0.6 Add go to the Current

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Slope Class box and in the drop-down menu select 2 go to the Class Upper Limit (%) box and

type-in 1.5 Add Reclassify Ok Overlay Ok

Explanation: The slope of each subbasin is taken into account to determine the areas of

each Hydrologic Response Unit (HRU). The Overlay command adds the landuse, soil and

slope layers to the ArcMap project file. A report on landuse, soil and slope distribution

can be found by going to HRU Analysis tab HRU Analysis Report.

Hydrologic Response Unit (HRU) Definition

1. HRU Analysis HRU Definition HRU Thresholds peg Multiple HRUs go to the

Land use percentage (%) over subbasin area box and type-in 10% go to the Soil class

percentage (%) over land use area box and type-in 10% go to the Slope class percentage (%)

over soil area box and type-in 10% Create HRUs Ok

Explanation: The distribution of HRUs within each subbasin is calculated based on the

landuse, soil and slope layers. The interface allows the user to specify criteria for landuse,

soil and slope to be used in determining the HRU distribution. One on more unique

landuse, soil and slope combinations can be created for each subbasin. Runoff is

simulated separately for each HRU and routed to the stream channel in the subbasin.

Input the Weather Data

Search and find the weather stations and database Go to http://www.ncdc.noaa.gov/cdo-

web/search

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For Weather Observation Type/Dataset Choose Daily Summaries

For Select Date Range Beginning: Jan. 1, 1975 End: Dec. 31, 1976

For Search For Select Stations

For Enter a Search Term GHCND:USC00412902

Then press Search

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Only one station should appear Click Emory, TX, US

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Click ‘ADD TO CART’

Hover the mouse over ‘Cart (Free Data) 1 Item’. Click on View All Items (1).

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Make sure that the Date Range is Jan. 1, 1975 to Dec. 31, 1976. Select ‘Custom GHCN-Daily

CSV. Click ‘Continue’.

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Check ‘Station Name’, ‘Geographic Location’, ‘Precipitation’ and ‘Air Temperature’. Click

‘Continue’. Type in your email address and press ‘Submit Order’. The weather data will be sent

through email.

Note: During the day, the email will be sent quickly, but after 6 pm it takes a lot longer!

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Click the download data button to get the data.

The weather data format will need to be changed for input into SWAT. Four files are needed.

a. PCP_FORK.txt (includes rain gauge info)

b. TMP_FORK.txt (includes temperature gauge info)

c. pcp_emory.txt (includes dates and precipitation in mm)

d. tmp_emory.txt (includes dates and max and min air temperatures in oC)

First, make the PCP_FORK.txt file

Open notepad in the first line put ID, NAME, LAT, LONG, ELEVATION as shown in the

figure below in the second line put 1 (station ID number), pcp_emory (file name for precip

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values), lat (location of weather station in decimal degrees), long (location of weather station in

decimal degrees), elevation (of weather station in meters)

Second, make the TMP_FORK.txt file

Open notepad in the first line put ID, NAME, LAT, LONG, ELEVATION as shown in the

figure below in the second line put 1 (station ID number), tmp_emory (file name for

temperature values), lat (location of weather station in decimal degrees), long (location of

weather station in decimal degrees), elevation (of weather station in meters)

Note: As shown below, the NOAA air temperatures are in tenths of degrees C (0.1 oC) and

precipitation data is in tenths of mm (0.1 mm). But in SWAT, the precipitation data must be in

mm and the air temperatures must be in oC. Therefore the units must be converted in Excel using

the procedure shown below.

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Convert precipitation units from 0.1 mm to 1 mm

Open the NOAA data in Microsoft Excel copy the Precipitation and Min and Max Temp data

in a new sheet click the cell next to the first precipitation data type “=” , select the first

precipitation data, and type “/10” to convert the precipitation to mm extend it to the bottom of

the data.

Convert air temperature units from 0.1 oC to 1 oC and comma separated max and min air temps

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Use the same procedure shown above to convert air temperature from tenths of a oC to 1 oC.

Next, create a column with Min and Max air temperatures separated by a comma for input into

SWAT. Use the method shown below

It should look like the table shown below.

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select all precipitation data and copy Open a new notepad document make sure the

first date is in the correct format yyyymmdd (In this case, 19750101) paste the precipitation

data beneath the first date Save as pcp_emory.txt in your working folder (see example file

below)

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select all the comma separated air temperature data and copy Open a new notepad

document make sure the first date is in the correct format yyyymmdd (In this case, 19750101)

paste the air temperature data beneath the first date Save as pcp_emory.txt in your

working folder (see example file below)

Okay, let’s go back to the SWAT simulation.

1. Write Input Tables tab Weather Stations Weather Generator Data tab Select WGEN

user Ok Ok go to the Rainfall Data tab peg Raingages go to the Precip Timestep

box and in the drop-down menu select Daily go to the Locations Table box and click on the

open files folder icon Navigate to your working folder highlight the file PCP_FORK.txt

Open Ok go to the Temperature Data tab peg Climate Stations click on the open

files folder icon Navigate to your working folder highlight TMP_EMORY.txt Open

Ok Exit from the Weather Stations box.

Generate SWAT Input Files

1. Write Input Tables tab Write SWAT Input Tables Select All Create Tables Yes

Ok Exit from the input screen

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Explanation: Many of the input data files required by the SWAT model are generated by

this step.

***If the .wgn file is not being written properly an error message will prevent you from

continuing this step. In order to fix this issue you must go to the folder where you are saving

your files. Double click “SWAT 2012” to open the Access software. Go to the “wgnrng” and

locate the ‘PR_W1’ and ‘PR_W2’ fields in the “CRNAME” column. Add an underscore to the

end of both of these fields (So it should be ‘PR_W1_’ and ‘PR_W2_’). Save the file, close

Access and rerun the Write SWAT Input Tables.

Edit SWAT Input (Optional)

1. Edit SWAT Input tab click point source discharges. (In Example 2, we edited databases)

select point source discharges. There is only one point source. select ‘9’ ok Edit

point source inputs window is opened click Edit values go to select point source data type

select annual records go to observed loadings input files/Average Annual Daily loading

file click the folder icon select pointsyearly.txt (C:\Swat\ArcSWAT\Databases\ExInputs)

If you can’t see the txt file, change Files of type to txt files (*.txt) open click Cancel Edits

Exit Cancel

2. Edit SWAT Input tab Inlet Discharge select ‘8’ ok you can do the same way as

editing point source discharges. Exit

3. Edit SWAT Input tab Reservoirs select reservoir subbasin. There is only one reservoir.

Select it Ok click the Edit values Reservoir Data tap put the value 10000 RES_SED

(mg/L) click the next column value, and you will get out of range a message Click ok

In the Reservoir Management box IRESCO select Measured Daily Outflow go to

RESDAYO Table box click the folder icon highlight the resdaily.dbf

(C:\Swat\ArcSWAT\Databases\ExInputs\) If you can’t see the dbf file, change Files of type to

dBase files (*.dbf) Open go to Monthly Data tap go to Lake Water Quality Data tap

Cancel Edits Exit Cancel

Explanation: Monthly Data controls the constant monthly parameters of the reservoir.

Lake Water Quality Data control the water quality parameters of the reservoir.

Setup SWAT Simulation

1. SWAT Simulation tab Run SWAT Start Date: 1/1/1975 Ending Date: 12/31/1976

go to the Printout Settings box and peg Monthly Setup SWAT Run Ok Run SWAT

Ok Fini!!!

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Explanation: The dates of the SWAT simulation and the printout frequency is specified in

this step. More SWAT input data files (CIO, COD, PCP.PCP and TMP.TMP) are

generated at this time. The Run SWAT command runs the SWAT executable file.