Part I. Building the Watershed Model

How to Model Watershed
A typical watershed drainage basin

A simple watershed has been constructed and shown below and will be the topic of this tutorial. Here you will learn how to add hydrographs to a basin model and how to connect them based on the watershed configuration. This tutorial is only about learning watershed connectivity, not detention pond modeling.

Like all watersheds, you’ll begin at the uppermost drainage areas and work downstream, adding runoff hydrographs along the way to your basin model, and connecting them together when appropriate. Watershed simulation is accomplished by selecting the appropriate function(s) from the Ribbon menu in the order of the sub-catchment connectivity.

This example watershed consists of three drainage areas (subareas) and an intermediate channel. Our task here is to develop the most downstream hydrograph which outfalls into a major lower horizontal channel.

To model the watershed shown below, follow these 5 easy steps:

  1. Create runoff hydrographs for sub-areas “DA1” and “DA2” — Hydrographs 1 and 2.
  2. Add (combine) Hydrographs 1 and 2 to form Hydrograph 3. (They converge at the same point, a confluence.)
  3. Route Hydrograph 3 through the intermediate channel to create hydrograph 4.
  4. Create runoff hydrograph for sub-area “DA3” — Hydrograph 5.
  5. Lastly, add Hydrographs 4 and 5 to create Hydrograph 6.

Following is a step-by-step procedure working from the “Basin Model” tab. We’ll disregard the input particulars such as drainage areas, CNs, etc. This will be covered in more detail in Part II. This tutorial is simply to illustrate the steps involved in developing a watershed “model” in Hydrology Studio.

Here are the steps in detail:

1. Add runoff hydrographs representing DA1 and DA2

With the Basin Model tab selected as shown below, click your mouse anywhere on the open canvas. Then click the [NRCS] button on the Ribbon menu.

An NRCS hydrograph icon will be placed near the top center of your screen. Click the [NRCS] button again to add the second sub-basin, DA2.

2. Add the two runoff hydrographs to create a junction

Since subareas DA1 and DA2 converge, we will combine these hydrographs to form a junction. This junction represents Hydrograph 3. To add or combine hydrographs, select them first by dragging a rectangle around them with your mouse or alternatively, click on the icons while holding down the [Shift] key.

Then click the [Junct] button on Ribbon menu.

Your model schematic will look like this:

3. Route Hydrograph 3 through the intermediate channel to create Hydrograph 4

Hydrograph 3 then travels down a channel (Intermediate Channel) which outfalls into the Main Channel. We must perform a Channel Route. Select Hydrograph 3 and click the [Reach] button on the Ribbon Toolbar.

The updated canvas will show the following schematic:

4. Add runoff hydrograph for sub-basin DA3

DA3 must be added to the model at this point because it also outfalls into the Main Channel. Simply follow the procedure shown in Step 1, i.e., click the [NRCS] button.

The updated basin model will look like this:

5. Combine Hydrographs 4 & 5 to create Hydrograph 6

At this point we have two hydrographs that outfall into the Main Channel. Since we only want a single hydrograph, we must combine (add) them. Select hydrographs 4 & 5 as you did in Step 2.

Then click [Junct] on the Ribbon menu.

Your final basin model should look like this:
Watershed Model - Hydrology Studio
Hydrograph 6 is the final hydrograph that flows into the Main Channel.

Watershed Model Complete

No matter how large or small, that is all that’s needed to build a simple watershed. Working from the most upstream point to the downstream point, simply create runoff hydrographs, add them to together at confluences, route them through channels or detention ponds, split them up (Divert) if needed, until you have reached the downstream point of interest.

Hydrology Studio requires that Hydrograph Numbers increase as you work downstream.

You can re-position any or all of the icons on the canvas to better mimic world conditions by simply dragging them with your mouse. You can also re-position groups of icons by holding down the [shift] key while dragging.

As you have noticed, we haven’t added any data to these hydrographs or computed anything yet. That is covered in Part II. Adding Data, Computing Results.

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