Contrasting River Styles
For this assignment, we were asked to find at least one confined, one partly-confined, and one unconfined riverscape within the same watershed. I chose Blacksmith Fork for the location of my project because I could easily visit this riverscape in person.
Blacksmith Fork
The Blacksmith Fork watershed is located in the Bear River Range in Northern Utah. This watershed is located directly south of the Logan River watershed. Blacksmith Fork is one of the larger tributaries to the Logan River. The watershed has an average temperature of 5.4 degrees celsius and receives ~ 752 mm of precipitation each year. With most of its precipitation occurring in the winter months, the flow regime of the river is highly dependent on snowmelt. As a result, the peak flows often occur in the spring/summer months when the temperatures rise and the snow begins melting. The majority of the 125 km^2 watershed is located in a limestone canyon with 40% of its landcover type being intermountain basins montane sagebrush steppe and ~20% being rocky mountain aspen forest and woodland. The two predominant ecoregions that make up the watershed are semiarid foothills and wasatch mountain zone; this can be seen in the image below. Overall, Blacksmith Fork exhibits a dendritic drainage pattern and has a mainstem length of ~ 47 km.
Unconfined Reach
This reach is located further upstream than the other reaches which is unusual for an unconfined reach. However, this is due to the river being dammed up directly downstream of this reach. As a result, the river has adjusted its base level to be the damn and therefore there is a decrease in flow and an overall increase in sinuosity. This reach has a very broad floodplain which allows for the river to adjust its channel during high flow. The majority of the bed material in this stretch of river is fine-grained as a result of sediment accumulation behind the dam. The increase in base level has also allowed for more vegetation to grow here which has created a somewhat swampy ecosystem. The cross-section below depicts how the valley bottom changes across this section of the river.
Partly-Confined Riverscape
This reach is located at the mouth of Blacksmith Fork Canyon and is located furthest downstream of all of the sites. This section of the river is partially confined by the road on one side and the valley bottom margin on the other. This reach has a gravel bed with a channel that has adjusted to the confinement of the hillslope. Ideally, the river would be able to laterally adjust in the valley bottom, but there is now a road that partially confines it on one side. During high flow, this river will not be able to laterally or vertically adjust very much and the road may flood since it is built of the floodplain of the channel. This reach currently has a smaller active floodplain than it would have had before the road was built. Unlike the unconfined reach, There is not much vegetation on the floodplain because there are pull-offs and a road running directly through this section's floodplain. The cross-section below depicts how the valley bottom changes across this section of the river.
Confined Riverscape
This reach is located roughly 1.5 km upstream of the partly-confined site. this reach is very similar to the partly-confined reach, but it is more tightly confined by the road. This section of the river has no room for lateral adjustment and in the case of high flows, the river can only just vertically. This would result in the road flooding so the river can utilize its floodplain which the road is built on top of. Once again, there is not much room for vegetation on the flood plain due to the road and pull-offs that were built on it. This is a predominantly gravel-bed river that is confined by the bedrock of the valley bottom margin. The cross-section below depicts how the valley bottom changes across this section of the river.
References
“10 meter USGS DEMs” Utah State Geographic Information Database. Utah Automated Geographic Reference Center, January 2018. Web. 30 April 2021.
“NHD Streams” Utah State Geographic Information Database. Utah Automated Geographic Reference Center, December 2016. Web. 30 April 2021.
“Watershed Areas” Utah State Geographic Information Database. Utah Automated Geographic Reference Center. Web. 30 April 2021.
“Dominant Vegetation” Utah State Geographic Information Database, Utah Division of Wildlife Resources. Utah Automated Geographic Reference Center, January 2001. Web. 30 April 2021.