This post is part 1 of a multi-part series of posts that aims to describe numerous ways in which Google Earth Pro (GEP) is useful as a visualization tool for water resources systems planning. (GEP is a virtual globe that lets you create and analyze geographic information). You can find Part 2 here.
Specifically, this post is designed to teach you how to create a visualization of a planned reservoir’s inundated surface area, given some basic information about a planned dam site. Dam development is on the rise in river basins around the world, particularly in Asia, Africa and South America. In conducting feasibility (or pre-feasibility) studies of dam development plans, it can be useful to prepare quick, simple visualizations of reservoirs.
Interestingly, Google recently eliminated what used to be a $400/year fee for GEP, so I highly suggest you use GEP instead of regular Google Earth (GE). GEP has several helpful features not available in GE, such as the ability to compute areas of polygons.
Before you try these exercises, I suggest you download/install the latest version of GEP from: https://www.google.com/earth/explore/products/desktop.html. On this website, scroll to the bottom of the page and click on “Download Google Earth Pro”. Agree to the terms, download and install. (At some point you may be asked for a license key. Assuming you do not have a key, use your email address and the key GEPFREE to sign in when prompted). I prepared these tutorials using version 126.96.36.1991 in Windows 7. Note that you can run both GE and GEP on your computer, so if you already have GE, I suggest you try this tutorial with GEP.
Suppose we have the following information about a planned dam (MRC 2014, see references section for data source):
a.) Dam coordinates:
Latitude: 15°58’30.00″N; Longitude: 106°55’50.16″E
b) Reservoir Full Supply Level (FSL) elevation (meters above sea level): 490 masl. Let’s assume the FSL represents the upper elevation of the impounded reservoir’s active storage zone.
Follow these steps to create a placemark for the location:
- First, create a placemark by clicking on the “Add placemark” button (a yellow pushpin graphic) in the toolbar at the top of the screen. A “new placemark” window will appear. Enter a name for the dam (in the screenshot below, I call it “MyDam”), the dam’s latitude and longitude coordinates as they appear above, and any description you wish to add. It doesn’t matter where you are in the world on your screen, GEP will locate the placemark wherever you tell it to.
(Hint: before you create the placemark, you may want to zoom in a bunch using the slider on the right, as the placemark’s default view will be the one you have when you create the placemark, which makes it harder to see the pin if you’re zoomed out too much).
- In the same “New placemark” window, switch to the “View” tab, and enter the dam’s coordinates again, then Click “OK”.
- The placemark should appear in your “Places” list on the left. Double click on your Dam icon to zoom in on the location of the dam. (See the Hint from Step 1 if GEP doesn’t zoom in at all when you click on your placemark). You can zoom in on the placemark manually using the slider on the right of the screen. Your screen should appear something like:
Next, you will need to create a polygon that will ultimately represent the reservoir’s surface area. Follow these steps to do so:
- Create a new polygon by clicking on the “Add polygon” button in the toolbar at the top of the screen. (Right next to the placemark button).
In the box titled “Google Earth – New Polygon”, give your reservoir a name, such as “MyDam Reservoir”, and in the “Description” tab, add any description you wish to add.
- Switch to the “Style, Color” tab in the “Area” category to select a distinguishable color for the inundated area, such as blue.
- Use the cursor to drag over/highlight the area you want the polygon to cover (left click and hold down until you’re done covering the desired area), then Click OK. As is demonstrated in the image below, you will want to cover a fairly large area, because the reservoir you ultimately create will be a slice of your polygon at the FSL elevation. If your polygon is not large enough, your reservoir graphic may get cut off.
(Given that you don’t know what the reservoir looks like ahead of time, this can be a trial-and-error process). Note that if you hold the mouse over the GEP imagery, it lists elevation information in the lower right corner, so you can check elevations at upstream locations in the visible tributary and sub-tributary channels to see how far upstream a 490 m elevation might extend, to be sure your polygon covers that area.
If you make a mistake in drawing your polygon and wish to get rid of it and try again, you can right click on it and cut or delete it.
- Right click on your polygon, and select “properties”. Switch to the “Altitude” tab, and in the drop-down menu select the “Absolute” option. In the altitude box, enter the reservoir’s full supply level elevation (490 m).
- An approximate reservoir shape should now appear, and the polygon “MyDam Reservoir” should now appear in your “Places” list on the left.
If you zoom in on the reservoir, its appearance will take on a clearer form, as is shown below.
You may notice that the reservoir extends below the location of the dam. You can remedy this issue by editing the polygon’s control points. Right click on the polygon, and click “properties”. You will see the points appear in red (see image below). You can move some of the points up closer to the dam, as is shown below, to eliminate the blue polygon portion that extends below the dam.
Your polygon should now appear like this:
If you have managed to successfully follow all of these steps, you have created a simple visualization of what turns out to be the Xe Kong 5 dam/reservoir, planned to be constructed on the Xe Kong River in Laos, a tributary river to the Mekong River (MRC 2014).
Note that GEP may perform the process I’ve outlined here quite poorly in flat areas such as floodplains, where slight changes in elevation can create very large discrepancies in reservoir inundated area. This is why I selected a location characterized by relatively steep terrain.
Mekong River Commission (MRC) (2014), Hydropower Project Database, Basin Development Plan Programme, Mekong River Comm., Vientiane, Lao PDR.