Google Earth Pro: Another, Easy Way to Check on a Property’s Hydrologic History
Yesterday, I posted about the discovery of something called the Odom Lake Swamp on a 70-year-old map. Many of the homes that flooded in Elm Grove on May 7 were built in or near it. But learning that required scaling and aligning maps in Photoshop. It’s a time consuming process and not everyone has Photoshop. If you’re considering buying a piece of property, luckily, there’s an easier way to check on its past: the history function in Google Earth Pro.
History Function In Google Earth Pro
Google Earth Pro contains dozens of aerial and satellite images that are already scaled and aligned. The program is a free download and makes scrolling back through time simple. When you first open the program, you’ll see a map of the world. Click on the area that interests you to zoom closer in steps.
- From the menu at the top of the screen, select “View/Historical Imagery”
- Click on the Clock icon in the menu bar.
- Arrows and a timeline will appear at the top left of the screen.
- Scroll back and forth through time by clicking on the arrows.
- To show streets that exist today (but that didn’t exist when the image was taken), select View/Sidebar. Then check Labels/Borders and Roads.
Here’s what you see when you scroll back to 1978 (minus the red circle which I added to highlight the area of interest).
Looking at this, you wouldn’t have known that the large flat, featureless area was called Odom Lake Swamp. But you could tell that something unusual was going on there. And that might tell you to dig further into the area’s history.
“Reading” Satellite and Aerial Images
Google Earth Pro doesn’t show contour intervals as a topographic map would. Nevertheless, it can still tell you a lot. Flat featureless areas like this in the middle of dense forests can indicate ponding, at least on a seasonal basis. Translation: Low area.
Note several other discontinuities in the image above:
- A small pond in the lower left (north of Sherwood Trails)
- A depression near the upper left that interrupts the straight white line
- A triangular area in the upper right where no trees are growing.
In the image below, I zoomed in closer on the Odom Lake Swamp. The image shows what at the time was a dry lake bed. Taylor Gulley had just reached the area and had most likely drained what was a seasonal pond or swampy area. Taylor Gulley itself (bottom right) had not yet been excavated to the county line (thin green diagonal line in upper left).
Nature Never Forgets
As one expert told me: “Where old channels, swamps, meanders, etc. were filled in, during major floods, water always seeks the lowest point. Even if you fill in an area, it usually is still the lowest point of a larger area (or watershed) and during large rain storms, the water finds its way there.”
It only takes a one degree slope to make water move across concrete (two degrees through grass or foliage). That’s barely visible. It underscores the need to consult maps and tools like Google Earth when buying property.
Awareness of potential problems is your best way to prepare for or avoid them.
Google Earth can help in this regard. As does FEMA’s National Flood Hazard Layer Viewer.
Posted by Bob Rehak on 6/20/2019
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