Week 3 - St Vrain River (locally known as)

  

Since I live in Longmont Colorado, I didn't have to go far to explore an interesting source of running water. The St. Vrain Creek or St. Vrain river as it is known locally, "is a tributary of the South Platte River, approximately 32.2 miles long in north central Colorado. It drains part of the foothills north of Boulder and the Colorado Piedmont area in the vicinity of Longmont. The creek is formed by the confluence of North and South St. Vrain creeks at Lyons. The creek rises in several branches in the foothills of the Front Range northwest of Boulder. St. Vrain Creek is joined by Left Hand Creek south of Longmont and Boulder Creek east of Longmont." 

We really enjoyed watching how the river change as we followed its meandering path through the canyon on our way to Estes Park. Parts of the river were moving so slow it was hard to tell if the were moving at all. Other parts were flowing fast enough to create a white water effect. We could see where certain parts branched off creating a secondary, much smaller flow in and old path.

While St. Vrain Creek is typically a slower moving and calm river, in September of 2013 that changed. In 8 days, 17.15 inches of rain fell causing the St. Vrain to swell and overrun its banks, violently carving itself a new path. During the flood, the St. Vrain rivers (north and south) carved through Big Thompson canyon, dragging large boulders down stream, knocking over huge trees and taking out the road (due to erosion of the underlying ground) between Lyons and Estes park changing its flow path and the surroundings forever.

Because this river is perennial we enjoy visiting the canyon year around, exploring the banks of the river and watching the mountain landscapes change. During the summer, we as a family have enjoy a calm area of the creek in Lyons where you can tube and picnic on the bank. We had visited this area many times before but since the flood the landscape looks much different. The fast and high flowing water carved out new banks and shore lines near the river bed exposing hidden layers of red sandstone (with a unique salmon color) and limestone that had been hidden up until now. Because limestone can be easily eroded, it was easy for the powerful flow to take down 100 year old trees leaving an amazing view of the sandstone cliffs that surround the town of Lyons on 3 sides. These cliffs are composed of "ancient deposits of the 250 million-year-old Lyons sandstone found along the eastern flank of the Front Range" and were created by the flow of water millions of years ago

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The Big Thompson canyon contained a wide fairly flat floodplain from a previous flood that allowed a guide for the river when it began to flood again in 2013. When driving up the canyon on our recent trip, you could see where the river used to run, where it went during the flood (due to landscape disturbance and debris) and where the river runs now. The new wider floodplain is subject to another huge flood but hopefully the restoration of the landscape will lessen the effects when it happens again.

Refrences

https://en.wikipedia.org/wiki/St._Vrain_Creek 

http://coloradogeologicalsurvey.org/colorado-geology/sedimentary-rocks/ 

Lutgens, F. and Tarbucks, E. (2016). Essentials of Geology: Chapter 13, Running Water.  New York, NY: Pearson. 

https://www.bing.com/images/search?q=st+vrain+river+lyons+2019&FORM=HDRSC2

During the 2013 flood

Landscape change before and after the flood