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Data from the sky informs flood planning on the ground Posted on September 16, 2020



Manuel Razo—Flood Mapping Manager, Texas Water Development Board

Flooding is a serious problem here in the state of Texas; we experience various types of flooding. So, one way that we want to really represent that and address some of those issues is through providing mapping services statewide, and we want to use accurate data. And so, in order to do that, we use the lidar data, and that provides a really detailed representation of the terrain. 

We need to have this up-to-date, accurate depiction of what the flood risk is, and that's through up-to-date science. And we need that lidar data to better understand that.

Joey Thomas—Strategic Mapping Project Manager and Elevation Specialist, Texas Natural Resources Information System

Lidar data creates a very detailed representation of the earth’s surface. Lidar stands for light detection and ranging. Typically, there is a laser and a sensor mounted to the bottom of a plane. And as the plane flies over the surface of the earth or the area you're surveying, it pulses a laser at hundreds of thousands of times a second. What is measured is the time it takes for the pulse to hit the ground and return to the sensor on the bottom of the plane. And using that time lapse, they can calculate what the distance from the plane to the earth is.

The final data set produced by a lidar acquisition can give you information about anything on the earth's surface. So, because you can filter out portions of the point cloud, such as vegetation and buildings, you're left with just the ground surface. And that surface can be used to more accurately represent flooding and flood modeling and doing the baseline engineering required for FEMA floodplain mapping.

Manuel Razo—Flood Mapping Manager, Texas Water Development Board

So, in order for the flood planners to be able to identify areas that need mitigation, they need that updated science. And through the lidar, it provides the data that we need to go in there and do the modeling and identify the flood risk areas.

Older floodplain maps were derived off of the old U.S. Geological Survey 30-meter or 10-meter digital elevation models. It was a representation of the terrain, but it was a 30- by 30-meter grid. Where now, we use a 1-meter by 1-meter grid to represent the terrain. So, it's a lot more detailed and accurate. It gives us that real detailed picture of the terrain to understand where the high spots and the low spots are. And you know, the low spots are, tend to be the ones that are more susceptible to flooding.

As the state grows, we get more development; we get more people moving in, which we're seeing right now. We can get that lidar, and it will be reflective of what's happening on the ground so that we can better model and better understand what's going to happen during a flood.


Recent lidar acquisitions in Central and North Texas

Joey Thomas—Strategic Mapping Project Manager and Elevation Specialist, Texas Natural Resources Information System

"This past winter during the leaf-off season, the Strat Map Program collected lidar data in the North and Central Texas regions. In Central Texas, we collected an area along the I-35 corridor that stretched north and south of McLennan County. The main reason why the refresh cycle is needed is because of land cover change. And as the land cover changes, especially in areas along the 35 corridor, and areas north of the Metroplex, there's been urban sprawl in addition to substantial amount of construction along I-35. And so those areas would benefit from having updated data, especially data that is nearing almost 10 years old, by the time the new dataset gets released."

This article is posted in Flood / Technology .