Dr. Nelson

Model Setup

Delineate Judy's Branch Watershed

You may use an existing delineation, but it is probably easier to start from scratch with your DEM DataThe NRCS provides

county-level (SSURGO)andstate-level (STATSGO)soils data that includes hydrologic soil group attributes. We want you to visit the NRCS sites through the GSDA web page and you may choose to download the data for Judy's Branch (Madison County). These data sets are large and can take some time to download so you can use my copies of the data previously downloaded SSURGO, and Illinois STATSGO. You should know enough about the NRCS site that you can download data for your projects later on.Load the shapefiles into WMS and then right-clicking on the layer and choose the option to join the NRCS data (Note that this option is not available in the Wizard currently).

Download the land use shape file(s) for Madison County (Judys Branch is in this county of Illinois). You can follow the links on the GSDA website for downloading landuse (use the WebGIS link which is the first one in the list). Click on the button under Web GIS, click on Land use, select coordinate system, select state and select county. These files are small enough that each team can download separately.

Create WMS soils and land use coverages from the shape files downloaded.

Notes: You will have two separate soil coverages, one from the SSURGO data and one from the STATSGO data that you will use to compare. When you load the shape files you will discover that they are Geographic NAD83 and you will have to convert to UTM NAD83 Zone 16 (or 15 depending on what you have beenw working in). Be sure to map soil polygons to the soil coverage and land use polygons to the land use coverage. It is also recommended that you select only the land use and soils polygons overlapping the watershed (particularly for the case of SSURGO data which has thousands of polygons, but many of which are not over your watershed).

For the land use data you will need two shapefiles. You can load both, convert the coordinates and then select the polygons overlapping the watershed and WMS will map the appropriate polygons to a single coverage from both shapefiles.

You can use Calculators | Compute Coverage Overlay (in the hydrologic modeling module) for the drainage and land use coverages to determine which land use types overlap your watershed boundary. For these land use types determine CN values for all four hydrologic soil groups for the three antecedent moisture conditions (pg. 158 Wanaliesta - CE 431 Hydrology Text Book and WMS TR55 documentation). You can define these CN values in WMS from the attributes of the land use polygons or importing a text file that you create (using an existing one as a template).

Use the Compute Coverage Overlay for the drainage and soil coverages to determine which hydrologic soil groups overlap your watershed boundary. For these hydrologic soil types determine appropriate Green and Ampt Parameters. The Green and Ampt parameters are discussed in page 42 of the HMS Reference Manual. You can also see this document which you will find to be useful.

In this assignment we will be looking at different parameters in HMS that affect infiltration and perform some of the sensitivity analyses between different methods, and parameters used to define them. You may use any starting and ending dates but make sure that your simulation runs long enough to capture the complete hydrograph..

Processes:

1. Curve number sensitivityHere you will see how the variation in curve number affects the runoff. The CN variation is done on the basis of antecedent moisture condition of soil. (pg. 158 Wanaliesta - CE 431 Hydrology Text Book, Appendix 1 of the HMS reference manual, and WMS TR55 documentation). You will compare the runoff hydrographs from different CN cases.

Watershed: Single Basin, Use SSURGO soil (Note it takes longer to compute CN because there are more soil polygons).

Loss Rate Method: Computed CN for Condition 2 (Normal), Condition 1 (Dry), and Condition 3 (Wet). You could create a table for dry/wet condition, or you can just adjust the composite value and change in HMS, but remember to update initial abstraction also.

Initial abstraction: Use 0.2S Where S = (1000/CN) - 10, remember this changes as CN changes.

Transform method: Clark

Lag time: SCS equation (This also changes with CN.)

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

2. Initial abstraction sensitivityHere you will see the effects of initial abstraction on runoff hydrograph. Use normal condition CN and simulate with Ia of 0, 0.1S, 0.2S, and an appropriate value as suggested on page 39 of your reference for estimating initial abstractions. You will compare the hydrographs from different initial abstractions.

Watershed: Single Basin, Use SSURGO soil

Loss Rate Method: Computed CN for Condition 2 (Normal)

Transform method: Clark

Initial abstraction: Use 0, 0.1S, 0.2S and an appropriate value as suggested on page 39 of the HMS reference for estimating initial abstractions Where S = (1000/CN) - 10

Lag time: SCS equation (This also changes with CN.)

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

3. Soil Type sensitivityYou have downloaded two different soil types with the county level and state level resolutions. In this part we will see how the soil resolution affects the runoff. So, determine CN from i) SURGO soil and ii) STATSGO soil. Use these curve numbers and simulate. you will compare the hydrographs from two different soil types.

Watershed: Single Basin, Use both SSURGO and STATSGO soils for computing different CN's from the table previously compiled.

Loss Rate Method: Computed CN for Condition 2 (Normal) using i) SURGO soil and ii) STATSGO soil

Transform method: Clark

Initial abstraction: Use 0.2S Where S = (1000/CN) - 10, remember this changes as CN changes.

Lag time: SCS equation (This also changes with CN.)

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

4. Initial and Constant-rate Method (Single Basin)This is the most basic loss rate model. You can estimate parameters relatively easily, however it is difficult to know the right values without performing some kind of calibration. We'll use this model to compare to the SCS and Green and Ampt methods.

Watershed: Single basin, Use SSURGO soil

Loss Rate Method: Initial and Constant-rate Method. Use your soils and land use data to estimate parameters from the information on pgs 38-39 of the HMS reference.

Transform method: Clark

Lag time: SCS equation (Use a CN = 69.5 for this calculation)

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

5. Green and Ampt Method (Single basin)Another method to consider the infiltration is the Green and Ampt method. The parameters are determined based on the soil and land use information. As already explained use the references stated above and estimate Green and Ampt Parameters and simulate. You will compare the results form Green and Ampt with the results from Single basin HMS (With SSURGO soil Normal condition, Ia = 0.2S). Be sure to save this model as you will use it to adjust % impervious in a comparison with GSSHA in the next assignment.

Watershed: Single basin, Use SSURGO soil

Loss Rate Method: Green and Ampt

Transform method: Clark

Lag time: SCS equation (Use CN = 69.5 for this calculation)

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

Note: If you get 0 runoff try adjusting moisture deficit to 0.0 (saturated), or decrease hydraulic conductivity until you see some runoff - be prepared to comment on what this means?

6. Spatial variation sensitivityIn this section, you will divide the watershed into two sub basins. Your watershed should look somewhat like this. You have to route the hydrograph from right basin to the outlet. Use the following methods.

Watershed: Two basins, Use SSURGO soil

Loss Rate Method: SCS method

Initial abstraction: Use 0.2S Where S = (1000/CN) - 10 (Different value for each sub-basin)

Transform method: Clark

Lag Time: SCS equation (Different for each sub-basin)

Routing: Muskingum method with Muskingum K = 2.5 hrs, Muskingum X = 0.25 and Number of sub reaches = 10

Precipitation: 2.5 inches with a Type II temporal distribution.

Model Run: 36 hrs @ 6 mins interval

7. Gridded SCS Method with MODClarkFinally, you will use the distributed model to see the effects of lumped and distributed parameter models on runoff. Use 100 by 100 MODClark grids and compare the results with Single basin and two basin HMS models with SSURGO soil and Ia = 0.2S.

Watershed: MODClark Grids, Use SSURGO soil

Loss Rate Method: Gridded SCS method

Initial abstraction ratio 0.2, potential retention = 1.0.

Transform method: MODClark method

Lag Time: SCS equation (Use CN = 69.5 for this calculation)

Precipitation: 2.5 inches with a Type II temporal distribution.

NOTE: You must define this as a user hyetograph option.Model Run: 36 hrs @ 6 mins interval

To turn in with modeling exercises:

Hydrographs from all of the above scenarios. Download the template found here and copy and paste in your outflow hydrograph values from HMS into the appropriate column. The graphs should already be set up, but feel free to include any other graph of interesting comparisions you think of. The template will only work if you correctly set up your models to run for 36 hours at 6 minute intervals.

To turn in with losses review (but at least think about these now):

Comparison from the curve number sensitivity

Comparison from Initial abstraction sensitivity

Comparison from soil type sensitivity

Comparison from the SCS, Initial and Constant Rate, and Green and Ampt methods

Comparison from spatial variation sensitivity using the SCS method as a single basin, two basins, and with MODClark

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