How to Setup Idf Curves in Hydrology Studio

Welcome to Hydrology Studio. My name is Terry Stringer and I’m the chief software architect for this product and today, I’m going to show you how to setup your rainfall intensity-duration-frequency curves. More commonly called, IDF curves. I’m going to demonstrate this in Hydrology Studio but the procedure is identical to the one you would use in Stormwater Studio. As you may have noticed your software has been preloaded with sample IDF curves which you can use to get yourself acquainted with the product. Here’s how to setup your own local data. Start by clicking the Rainfall button located on the Ribbon menu. That opens up the Rainfall IDF Wizard. The Wizard uses a modern-day Ribbon menu located along the top. The current IDF curves are shown on this graph where you can see the 2, 5, 10, 25, 50 and 100-year frequencies. You can develop 1 and 3 year frequencies as well but the ones shown here do not use those. The horizontal section of the curve indicates the user-specified Minimum Tc. You can also view the curves in numerical form by clicking on this Table tab. The top row of this table are the current Frequency Correction Factors which I’ll go over in a few minutes. All IDF curves, no matter what method was used to develop, are equation-based. So even though the graph only shows intensities up to 120 minutes, there’s really no time limit. To setup new curves, click the “New” button. This opens a Wizard which will walk you through a series of steps. To start, you have three options on how to build your curves. 1. Create using rainfall map data where you’ll enter precipitation values directly from either Hydro-35, NOAA Atlas 2, or NOAA Atlas 14. 2. Enter intensities directly from your existing IDF curves or also from NOAA Atlas 14. And the third method allows you to directly enter the equation coefficients. Let’s do option 1. And we’ll choose the Eastern States. Here, we just need to enter six numbers. That is, the 5, 15 and 60 minute rainfall amounts for the 2 and 100-year return periods. Note that these rainfall amounts need to be in whole inches. Not intensities. The easiest and fastest way to get these numbers is by visiting the NOAA website. To do that, just click the NOAA button on the ribbon menu. Assuming you have an internet connection, that opens up a Precipitation Frequency Data Server. Now just select your state. For our example, I’m going to choose Pennsylvania. Pennsylvania is a NOAA Atlas 14 state with updated data so we can get what we want directly from this screen. Notice at the top, where it says, “Data Description”. Set the Data type to “Precipitation Depth”. If you were using Option 2 at the start of this wizard, where you would enter Known Intensities, you would choose “Precipitation Intensity” instead. Now, on the map, drag the red crosshair to the exact location of your choice. We’re going to use Pittsburgh for this example. Once you’ve selected your exact location, the table below populates with that location’s rainfall data. And it is this table where we’ll get our rainfall amounts. Again, we’re looking for the 5, 15 and 60 minute rainfall amounts for the 2 and 100-year return periods. And we’ll just enter those in real quick. The 2-year, 5 minute value is 0.376 inches. The 15 minute is 0.718 and the 60 minute value is 1.18 inches. Likewise, the 100-year, 5 minute precip is 0.71. The 15 minute is 1.33 and for the 100 year, it’s 2.56. Now click Next. That’s pretty much all you need to do. This next screen shows a table which lists intermediate intensity values derived from the rainfall amounts we entered. Click next again. This screen shows the actual coefficients for the equation that was developed for these curves. The top row shows the frequency correction factors. It is on this screen where you specify those factors. The default is set at 1. Clicking Finish takes us back to where we started. And this is what IDF curves look like in Pittsburgh, PA. I suggest changing the Title to the curves. You can just freely enter anything you wish. I’m going to enter Pittsburgh, PA. Your last step is to Save the curves. Do this by clicking the Save button and choosing a folder and entering a filename. I’ll use PittsburghPA for this tutorial. Hydrology Studio will automatically open the last IDF file that was saved upon its next launch. There’s no need to reopen each time. If you’d like a hard copy report of these curves, simply click the Report button and the document viewer opens up where you can preview before printing. Thanks for watching and thanks for choosing Hydrology Studio.