Tips for Long Term Precipitaiton Simulations

The Watershed Modeling System (WMS) has several options for modeling rainfall events, however many of them are built to model only single rainfall events. If you are looking to create long term simulations that include precipitation, the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) models may be the best fit for your projects. GSSHA was engineered with long term simulations in mind. GSSHA is a product of the US Army Engineer Research and Development Center (ERDC) Hydrologic Modeling Branch, in the Coastal and Hydraulics Laboratory. This blog post covers some information that may be helpful for the next time you build a long term simulation with precipitation.

Example of Long Term Precipitation Results in WMS

While HEC-HMS models are also capable of running long term simulations with precipitation, unlike GSSHA, long term projects are not the main focus of the model. If you’ve already gotten started with HEC-HMS, you may want to consider converting your project to GSSHA. We even have a tutorial that can walk you through doing just that.

There are multiple methods you can use to define precipitation data in GSSHA: Uniform, Gage, Hyetograph, and Nexrad Radar. This is done in the GSSHA Precipitation dialog. Rainfall data for GSSHA models are input as a series of single rainfall events. WMS calculates evapotranspiration between each event, which makes evapotranspiration data a required component of the simulation. There’s no limit to how many times the pattern of rainfall events and evapotranspiration can be repeated, or for what duration, as long as you have enough data.

If your model is not running as expected, there are a couple simple things you can check first when trouble-shooting your project. Be sure to check that you have included enough precipitation and hydrometeorological data. Not including enough data in your project can result in a faulty output. Each data point must be tied to a single point in time, down to the minute.

GSSHA uses gage and HMET files for precipitation and hydrometeorological data, respectively. This data can be prepared using the Time Series Data Editor application so that it can be imported into WMS for use in a long term simulation. Formatting this data properly can be a bit finicky at times, so you may need to double-check that everything is getting read in correctly. We have a tutorial that can show you how this process works, as well as many other tutorials covering different aspects of GSSHA in the WMS Learning portion of our website.

Head over to WMS and try these tips to keep your long term GSSHA simulation running smoothly.

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Using STL Files in SMS

Starting in SMS 13.0, SMS can now make use of STL files.

STL files use tessellation, the process of mimicking a surface by assigning surface coordinates to a repeated pattern of polygons. In the case of STL files, triangles are used to make a 3D mesh that can effectively be rendered into any shape needed including landscapes.

STL files are typically used for 3D printing. They also can be used for the modeling landscapes. There are several methods for creating these files. This post will not attempt to cover the specifics of those methods as other places cover how do this.

Uploading and Using STL Files

In SMS, STL files are used to model terrain. Once you have created an STL file, importing it by using the File | Open command or dragging-and-dropping the file into SMS.

When uploaded, the file is automatically transformed into a Ugrid and adjusted for the associated z values. This UGrid can then be used for all the normal uses of such in SMS.

Example of an STL file loaded into SMS

It is important to mention that the z values may or may not be representative of the elevation depending on the source of the STL file used. Fortunately, there is a way to handle such cases in SMS. After import, the Ugrid can be converted into a 2D scatter dataset. The scatter can then be interpolated to a mesh or modified with the data calculator. If desired, tim and dim files representing that data can then be created as usual.

Exporting STL Files

To create an STL file, you must have a UGrid with the corresponding elevation data attached. This UGrid must consist of only triangular elements.

Export the STL file by:

  1. Right-click on the UGrid and select the Export command.
  2. Then select a (*.stl) file type before saving the file.

There are two STL file type available for export. The binary option is often used since it requires less memory. The ASCII file is more user friendly if the file needs to be inspected. Both save data by recording the coordinates of the vertices associated with each triangle. If unaccompanied by other files, the Ugrid will also have to be manually associated with the correct projection after uploading.

We hope to add more functionality for STL files in the future. Try using STL files with your SMS projects today!

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