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 An Oblique View of Terrain Mapping
Ryan Hamilton
Ryan Hamilton
Ryan Hamilton majored in Environmental Studies at the University of Colorado and has been employed within both the LiDAR and IFSAR mapping worlds since 1998. His interests (that all appear to be tied to mapping) include blue water sailing, backcountry skiing and big mountain and downhill mountain … More »

In the Middle of the Boulder Flood

 
September 23rd, 2013 by Ryan Hamilton

The bread and butter of terrain data and DEMs have always been hydrologic modeling. The reason is simple, water follows the rules, it goes downhill and terrain will determine where the water will go, or so I thought…..

As I write this, I am in the middle of an actual flood. Boulder, Colorado is experiencing a 100 year flood event and it has been an eye opening experience to see the difference between a model and the real world.

Our house sits on top of a ridge about 80 feet above flood level and 1200 feet away from the nearest drainage channels. If you evaluated a typical fluvial flood model, our house would be shown as well above flood levels of even a 500 year event. The problem is that the typical fluvial model only works when you focus on the drainage channel as the source of flood. In a pluvial event, where rain comes down faster than the drainage infrastructures can handle, the use of terrain data alone as an input for predicting the water movement is not enough. Not only must you know drainage infrastructure capacity but you need understand geology and the permeability of the soil, as well as the actual soil saturation.

In our situation, we felt our house was safe since, not only, are we located on a ridge top, but our lot is raised about 10 feet from street level on all sides and has fall away slopes all around it. So I felt pretty certain that we would be safe from water intrusion. But when it rains a year’s worth of rain in 12 hours – all bets are off. Despite all of our favorable terrain, I have a very wet basement and a new appreciation for the complexity of flood models

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Category: Oblique view of terrain data

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