Revision as of 16:22, 15 July 2011

This document and the software GSSHA™ are products of the Hydrologic Systems Branch, Coastal and Hydraulics Laboratory, U.S. Army Engineer Research and Development Center. For more information about GSSHA™ contact:

Dr. Aaron R.Byrd, PE
Hydrologic Systems Branch
Coastal and Hydraulics Laboratory
Engineer Research Development Center
3909 Halls Ferry Rd.
Vicksburg, MS, 39180

Aaron.R.Byrd2@usace.army.mil

CHL GSSHA Overview

Disclaimer: GSSHA™ is a reformulation and enhancement of the hydrologic model CASC2D. The CASC2D hydrologic model is Copyright 1995, 1996, 1997, 1998 by Fred L. Ogden, 1995 by P.Y. Julien and B. Saghafian. No part of this documentation may be reproduced without complete citation. The GSSHA™ code is continuously being improved. Changes in the source code and input/output requirements of GSSHA™ may be made by the authors at any time, without notice. No claims are made regarding the suitability of GSSHA™ for any purpose. The model GSSHA™ is written for research and educational purposes. Use GSSHA™ at your own risk. GSSHA and Gridded Surface Subsurface Hydrologic Analysis is a trade-mark of the U.S. Army Corps of Engineers.

Most of the images were produced by the Watershed Modeling System (WMS), which is copyrighted by Brigham Young University, 2013 and used under license. For more information on WMS please refer to http://www.aquaveo.com.

Microsoft and Excel are registered trademarks of Microsoft Corporation in the United States and/or other countries. No endorsement is made by Microsoft Corporation of this work or as to the suitability of Excel® for any of the processes described in this document

17   Nutrients

This tutorial is compatible with:

• WMS Version 8.2 and later
• GSSHA Version 5.0 and later
  
  

Disclaimer: GSSHA tutorial exercises do not represent real world conditions

Two types of reactive constituent transport are available in GSSHA. As explained in the GSSHA wiki, constituents can be simulated as simple first order reactants. The nutrient cycle can also be simulated with the Nutrient Sub-Model (NSM). In either case, the overall simulation methods within the GSSHA model are the same. Only the rates of mass absorption and decay are different. It is then possible to simulate nutrients as simple constituents, as well as simulating them with the full nutrient cycle.

Modeling of nutrients in NSM consists of three distinct parts. The first part deals with simulating the nitrogen (N) and the phosphorus (P) cycle in the soil, whereas the second part focuses on the transformation and loading of N and P species in the overland flow. The third part simulates the most important processes for N and P cycle, dissolved oxygen and phytoplankton kinetics and can be used as a basic in-stream water quality model.

Open the Base Model

1. In the 2D Grid Module select GSSHA™ | Open Project File.
2. Browse to the Judy's_Branch_tutorial/NSM directory and open the file named nsm1.prj.
3. In the 2D Grid Module select GSSHA™ | Save Project File.
4. Browse to the Judy's_Branch_tutorial/NSM/Personals directory and save the file as nsm1.prj.

Setting up a GSSHA simulation with NSM constituents requires first a running hydrology model that includes simple constituents just to see that the model is transporting constituents appropriately. Once this is working, the NSM constituents can be set up. This base model has already been set as a long term simulation model with two simple constituents, as well as precipitation data and meteorological data for one week. If you have questions on how to set a long term simulation model or a simple constituent model, please refer to the the Long Term Simulations Tutorial and the Simple Constituent Transport Tutorial.

Adding NSM Constituents

1. Make sure that your project has 12 coverages, 9 of which should be rainfall events as shown in Figure 1 . GSSHA™ should be the active coverage in the Project Explorer.

Figure 1

Figure 2

1. Select the 2D Grid Module if not already selected. Go to GSSHA™ | Job Control.
2. In the dialog box that opens, click on the box beside Nutrients to select this option. Make sure that Long Term Simulation and Contaminant Transport are also selected. See Figure 2.
3. Click on the Edit parameter button for Nutrients. In the dialog box that opens, you can see four tabs: Point-Source, Non-Point Source, Other and Uniform Properties as shown in Figure 3. click on the Other tab.

Figure 3

In the Other tab you will see a list of parameters. Only temperature and channel pH have values assigned. The other parameters refer to rainfall concentrations for each constituent. In real life, we may or may not know the rainfall concentration of each constituent being simulated and in this case values of zero can be assigned. In addition, these concentrations may vary for each rainfall event as they are dependent on pollution at a given time. For the purpose of this tutorial, enter the following values:

Notice that contaminant 1 (1 mg/L) and contaminant 2 (0.5 mg/L) are included in this dialog box. The concentrations should be the same as the ones previously specified in the contaminant transport dialog box.

1. Click OK to close the nutrients dialog box.
2. Next to the Long Term Simulation check box, click on Edit parameters . In the dialog box that opens, toggle on the Use Soil Contaminant Transport and enter the following: Top Layer depth:1m, Mixing Layer Depth:0.5m
3. Make sure your soil moisture depth is set to 1.5m. Click OK to close the Continuous Simulation Dialog Box. Click ok to close the Job Control Dialog box.

The next step in setting an NSM Model is to create a Stream Index Map. This map is used to input aquatic kinetic constants for the stream network.

1. With the 2D grid as your active module, go to GSSHA™ | Maps.
2. In the dialog box that opens, select the Index-Stream Tab
3. Click the Add button and rename your index map as "Stream". See Figure 4.
4. Click Done.

Figure 4

1. With the 2D grid as your active module, go to GSSHA™ | Map Tables. Values for Roughness, Evapotranspiration, Infiltration, Initial Moisture and Contaminants should already be defined. We will now fill in the values for Nutrients.
2. Click on the Nutrients Tab. You will see three drop down menus, one for a grid map, one for a stream map and one for a map table as shown in Figure 5. From the Grid Map Drop down Menu select "Uniform". From the Use Stream Map select "Stream" and from Map table Select "Aquatic Kinetic Constants".

Figure 5

1. Click Generate IDs . You will have one column of values as we are using a Uniform Index Map. Notice that in the Use grid map drop down menu you had the option of choosing between Uniform, Land Use, Soil Type and Combined Index Maps. The index map you use will depend on the nature of your model. The Uniform Index map can be used to set up your model and make sure it is working as it simplifies the setup, but it does not necessarily represent real-world conditions.
2. WMS populates the column with default values and we will use those default values in this tutorial. Notice that the dispersion coefficients were assigned values of zero. Please enter the following values:

1. In the Map Table drop down menu there are 13 other options that require values. Select each one of the map table options, and generate IDs for each one using the maps indicated in Table 3.
2. Input the values found also in Table 3.

The last step before saving and running your model is specifying the output files you want to simulate and display in WMS.

1. In the 2D grid module, select GSSHA™ | Job Control
2. Click on Output Control.
3. In the Data Type Drop Down Menu, select Nutrients-Overland.
4. You will see a list of nutrients that can be simulated in the overland flow. Turn output on for all of the nutrients.
5. Scroll down the Link/Node Data sets options. You will see a list of nutrient output that can be turned on for nodes in the stream network. Select all of them starting from Stream Nitrite and ending with Stream dissolved oxygen. Your dialog box should look something like Figure 6.
6. Click OK to close the GSSHA Output Control dialog box. Click OK to close the GSSHA Job Control dialog box.

Figure 6

Save and Run the Contaminants Model

1. In the 2D Grid Module select GSSHA™ | Save Project File.
2. Save the file as nsm1.prj
3. When prompted to replace the existing file, click yes.
4. Select GSSHA™ | Run GSSHA™.
5. When GSSHA™ is done running, make sure the option to Read solution on exit is toggled on and click Close.

View Results

There are several different outputs generated when running the model. In the outlet location, you should get two constituent graph solutions, one for Constituent Mass and one for Constituent Concentration.

1. In the Project Explorer, right-click on the Outlet Constituent Mass graph, located below the GSSHA™ solution folder (the folder with the letter "S" on it)
2. Select View Graph. You have the option of selecting the constituents you want to view. For example, for nitrite and organic phosphorus, the graph should be similar to the one in Figure 7.
3. Close the constituent plot.
4. You can follow the same steps for Constituent Concentration graph. A plot for the concentration of ammonium and organic nitrogen is shown in Figure 8.

Figure 7

Figure 8

To view overland contaminant mass and concentration, do the following:

1. In the 2D Grid module select Display | Display Options
2. Turn on the 2D Grid Contours.
3. Select OK.
4. In the data tree, right-click on OV_no2_mass under the solution folder.
5. Select Contour Options.
6. Under Contour Method select 'Color Fill.'
7. Click on Color Ramp. A dialog box as shown in Figure 9 will appear. Click the Reverse button.
8. Select OK.
9. In the OV_no2_mass Contour options dialog, the number of contours should be defaulted to 20. Reduce this number to 10.
10. In the Contour Method drop down menu that is defaulted as ‘use Color Ramp’, select ‘Specify each color’.
11. You will note that the colors have now a drop down menu. Change your first color from blue to white. Leave the rest as they are. See Figure 10.
12. Click OK to exit the dialog box.

Figure 9

Figure 10

A set of time steps appear in the right pane of your WMS window as you selected OV_no2_mass. Click around on a few of them between 2:45am-11:00p.m. on 08/24/2001. It would be helpful if we knew what the colors represented.

1. Right-click on OV_no2_mass in the data tree.
2. Select Contour Options.
3. Turn on the legend.
4. Click OK.

Your mass overland display for OV_no2_mass (08/24/01 at 9:45 am) should look something like Figure 11.

Figure 11

1. You can follow steps from 4-16 if you want to visualize the rest of the constituents. Units of mass are in g/s and units of concentration are in mg/L.

In order to visualize mass and contaminant concentrations along the stream network, we need to turn on the contours for the 2D Scatter Data.

1. In the project explorer, right click the Link/node icon. Select the Display Options dialog.
2. Turn on the contours for the 2D Scatter Data.
3. Select a radius and Z Magnification (try a radius of 4 and a Z magnification of 50). If the lines are too big, you might need to decrease the Z magnification.
4. Click OK.
5. Select Dissolved P mass in the 2D Scatter Data folder in the data tree. Make sure that the Dissolved P mass is also selected for the overland plane (Under the Solution Folder in the Project Explorer).
6. Select a time step other than the first one in the Properties window, such as 08/24/2001 between 7:00-12:00 am.
7. If you rotate into 3D mode , or change from plan view to perspective view , you will see the lines representing stream mass. In the properties folder you will see the time steps. As you select individual time steps the data for that time step both the 2D grid data and the 2D scatter data will be contoured.

Your display for Dissolved P mass on the stream network (08/24/2001 9:45 am) should look something like Figure 12:

Figure 12

If you want more information on the project results we can open the summary file and get information on this and the rest of the processes simulated.

1. Double-click on Summary File under the solution folder.
2. If WMS asks for your editor just click OK.
3. Look through the summary file. Notice the kinetics of overland, stream and soil column constituent transport. It is also good to check things like mass balance and the volume remaining on the surface
4. When you are done you can close the window.

This concludes the GSSHA™ NSM tutorial.