Fluvial Geomorphology - Assignment 1

 Overview

Observations of a short reach of the Blacksmith Fork River of Hyrum, UT were taken from 2:30pm-3:30pm on January 12, 2025. The selected reach was easily accessible due to its proximity to Hyrum City Park. At the time of observation, the weather was partly cloudy and temperatures were around 30° F.

The Blacksmith Fork flows from East to West at this reach. The West site was around 45 m downstream of the East site.  

The East site was just below the label for Hyrum City Park. Since our observations were taken in the middle of winter, around 6 inches of snow covered the ground and the trees had dropped their leaves. Thus, at this time of year the reach was more exposed than what is pictured above. The differences in our observations in January 2025 and this image from September 2023 suggest that there is substantial variability in shading due to tree cover over this reach throughout the course of the year. 

Additionally, the south-facing side of the canyon was much steeper and well-forested compared to the north-facing side. This is likely due to the differing amounts of sunlight received on either side of Blacksmith Fork Canyon in this area.

 Site Observations

 Observations:

• At the farthest East point I could see at this site (just past where Quinn is standing), there was a riffle. Downstream past Quinn and the willows, the flow became less turbulent and a pool and point bar were present.

• Substrate had a clear pattern from the top of the point bar to the bottom of the pool (south to north). The substrate on top of the point bar was medium-sized gravel and the water was quite shallow and slow moving.

• Moving down the point bar, the substrate became coarse gravel and the water became deeper and faster flowing.

• In the pool, substrate was mainly cobble-size with a few interspersed boulders.

• Low-hanging branches and logs were present on the West side of this site, adding habitat heterogeneity.

• Depth ranged from 1 in - 12 in at this site.

 Observations:

• The substrate size was wildly different at this site compared to the East site despite their proximity. Substrate size ranged from silt to medium-gravel at this site.

• A similar channel structure to the East site existed at this site, where the channel was shallowest on the south side and deepest on the north side. However, this site had a steep dropoff, was much deeper, and had less of a gradual increase in substrate size. This leads me to believe that this is not necessarily a point bar, and may have more to do with the heavily eroded south bank.  

• The south bank was much less stable than the south bank at the East site. The grass from the park went directly up to the water's edge, whereas at the East site there were rocks stacked on the south bank that separated the grass from the water. 

• On the western side, willows grew on both sides of the channel rather than just the south side.

• Depth ranged from around 6 in at shallowest to 4 ft at deepest.  

• In general, the water seemed less turbulent at this site than the East site. I hypothesize that this is due to the difference in channel roughness between the two sites.

 Field Sketches

 Observations:

• The cross-section would have looked much different at the West site. Instead of a gently sloping point bar, the dropoff was quite steep and the water was much deeper. 

• Willows lined the South side of the channel at both sites, whereas alder trees lined the North side of the channel. Why? Since this area is clearly managed/used by people, is that an intentional choice or natural? 

• The channel appeared to widen where the point bar was forming, then narrow around where willows had colonized the banks. This pattern appeared at both sites.

• The channel had clearly been re-routed to flow along the road (see Additional Photographs). With distance from the road, the channel seemed less engineered and more free-flowing, though not completely natural. The banks near the park boundaries appeared to be intentionally placed, rather than naturally formed (as pictured in the East view of the East site and on the left side of Figure 3). 

 Local Land Cover

 Observations:

• Land cover data supports the observation that south-facing slopes are forested whereas north-facing slopes are shrublands.

• Upstream and downstream of the observed reach are deciduous forest areas, but the observed reach itself was mainly within woody wetlands. This was supported by our field observations of willow growth in this area.

• Although the land surrounding this reach has many recreational areas (and therefore many potential direct points of contact with people), overall development in the area is low.