Catchment-Scale Controls on River Geomorphology: Logan Watershed

The Logan River watersheds mainstem begins in souther Idaho at the Utah-Idaho broader, where the river enters Utah and lives in the the central Bears River range till is deposits in Cache valley and joins the Little Bear River. Below is a map that highlights the relative location of the catchment in Utah.

The trunk of Logan river beings near Franklin basin in Idaho at 2,465 meters and descends to 1,344 meters at the Cache Valley floor where it drains into Cutler Marsh; the valley floor represents the base-level control of Logan River. Comparatively if we were to take a trip through time and flash back 18,000 years ago that number would be drastically different, during which time the historic pluvial Lake Bonneville's shoreline was at its highest. While what remains of Lake Bonneville today is the Great Salt Lake, many morphological impressions remain allowing geologist to infer the elevation of the historical shoreline at approx. 1,546 meters (Inkenbrant, 2021), indicating the base control of a historic Logan river.

The longitudinal profile (above) of Logan River above indicates the path water takes from the head waters to its deposition in cache valley, this graph allows for a few simple inferences and calculations to help better understand the energy, erosional patterns, and slope throughout the river path

• Concavity is calculated with the measured distance between the mid-point at river elevation and a line drawn from end points(A, demonstrated in the graph by the intersection of the blue and black line) divided by the total change in elevation (H)

  • • • • • Concavity = 2A/H

          • A=1900 m - 1561 m = 339 m , H=2,465-1342=1,123 m

          • 2(339)/1,123= 0.60, this value represents a concave river profile

• Knickpoints are major sudden changes in elevation often due to lithology differences along the riverbed which shows a difference in erodibility. Along the Logan river I notice one major change beginning near 33.8 km, this coincides with the beginning of the three dams located along Logan River near the mouth of Logan Canyon.

• Catchment area, these were provided through USGS calculations

  • 646.56 km^2

  • 646,560,000 m^2

• Catchment length is synonymous with the length of the longest stream in the catchment, indicating the length of Logan River

  • 83,200 m

  • 42,662 m is the length of the catchment along the axis

• Catchment perimeter length, I was able to use a measurement tool in USGS to get a rough calculation

  • 157,360 m

  • 157.36 km

• Circularity is a simple calculation that allows for a general understanding of how elongated or circular a catchments shape is

  • • • Found by taking the area of the catchment and dividing it by the area of a circle with the same circumference as the catchment

      • Circumference = 2𝝿r ,157.36 = 2*𝝿*r, r= 25.0578

      • Area= 𝝿r^2 = 3.14*25.0578^2 = 1,971.57

      • Rc= 646.56/1,971.6 = .3 , this low circularity ratio indicated that the Logan River catchment is strongly controlled by the geologic structure

• Elongation ratio (Er)is another similar calculation to indicate the shape of the catchment

  • • • Take the square-root of the area divided by the length of the catchment

      • Er = A^.5/L

      • (646.56)^.5/83.2 =.3, this low ratio indicates an elongate catchment and can also indicate a strong influence of geologic structure as well as slow drain times

• The last calculation that we will make to indicate catchment shape is the form factor (Rf) which utilizes the length and area similar to the Er , but indicates the potential for floods of high magnitude

  • • • Rf =A/L^2

      • Rf =646.56/ (83.2)^2 =0.09

• Catchment relief

  • Catchment relief (H) can be calculated with the highest point in the catchment and subtracting the elevation at the mouth of the river. In the Bear River range Naomi Peak (3038.91 m) is the highest elevation point and on the east aspect drains to the Logan River. This highlights the total fall of a catchment

    • • H=Emax -Emin

      • H=3039 -1344 = 1695 m

  • Relief ratio (Rh) can be utilized in the case of better understanding the average drop per segment of river by taking the catchment relief (H) and divides by the length (L)

    • • Rh = H/L

      • Rh = 1695/82.3 = 20.6 units

• Drainage density

  • Drainage density (Dd)can be calculate with the total length of the catchment network (L) divided by the area of the catchment(A), which is treated like a constant. This can be indicative of the complexity of the drainage network, how relatively old the network is and how it could influence the the movement of sediment and water. Area has been previously calculated, but a total length of the perennial network was required for computing I achieved this through a statistics feature in USGS

    • • Dd = L/A

      • Dd= 216.68/ 646.56 = 0.34

      • *this number is very low which could indicate a young network or possibly an insufficient network map

    • Understanding drainage patterns helps infer what lithology is controlling the network and how sediment is transferred. The Logan River catchment (below) most closely resembles a dendritic patter and tributary patterns support this. There is one mainstem with a few larger tributaries and additionally the confluence trends towards a shallow meet point angle. The drainage pattern implies no strong geologic influences.