Oct 02 2013

South Platte River Aerial Imagery at Peak Flood Stage

South Platte at US 34 just east of Greeley

It’s been a whirlwind here in the two weeks since the flooding! We’ve had a lot of our folks in the field doing everything from construction oversight to high water marking to assessments of some of the damage (from a hydraulic perspective at least).

Another area we’ve been involved with is the collection of digital aerial imagery. Working with the Colorado Water Conservation Board (CWCB) and several municipal and county entities, our folks (here at Ayres Associates) collected digital aerial imagery for the South Platte River from the Weld/Adams County line downstream to Sterling and the Poudre River and Big Thompson River from their canyon mouth to their confluences with the South Platte.

The flooding began roughly the Wednesday night of September 11. We had flights up to collect the imagery on Saturday, September, 14, 2013, only a few days later! The imagery was collected at a ground sample distance of approximately 29 cm. Roughly 500 aerial images were collected to support the development of the 12-inch resolution orthoimagery.

The picture at the top is of US 34 just east of Greeley, a portion of the road that they actually just opened (single lane each way) earlier today. The river got very wide at this crossing, as the portion of the road that was damaged was not actually at the main thalweg crossing!

The image below is of the Big Thompson at County Road 29 just upstream of the Loveland Water Treatment Plant. We visited this area before and after the peak of the flood, as I documented in an earlier post. In this aerial image, you can see the damage to the road on both sides of the channel. You can also see traces of how it overtopped the bridge.

County Road 29 at the mouth of the Big Thompson Canyon


This next image is of an area in southeast Evans, which is southeast of Greeley. Just look at the inundation of this neighborhood.

Southeast Evans

Here is a more zoomed out shot of E 18th Street not far north of US 34 and some of the pictures above. The width of the flow over the floodplain is unreal to see in an aerial image.


I have one more image from the dataset that I thought was interesting. Our flight timeframe caught most of the peak but as you move further downstream, you see that the peak has not reached as far as the imagery goes. In the image below, northwest of Fort Morgan, you can see on the left (west) that the peak is nearly in full force. However, to the right of the image, there is not quite the full width of flow quite yet. This stretch would be my guess as to where the edge of the peak flow is.

Edge of Peak Northwest of Fort Morgan

We will have more analysis of some of this imagery to come. Meanwhile, the long clean up and recovery along the Colorado Front Range moves forward.

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