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Modual 3 Assignment
Catchment Scale Controls on River Geomorphology in the Logan River Watershed
Map of Logan River Watershed
Figure 1 (Above): Map of Utah that gives spatial context, the Logan River Watershed is outlined in red. Figure 2 (Right): Map of Logan watershed.
Longitudinal Profile
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Longitudinal Profile
1. Base Level Control of the Logan River today is 1344 meters along the fault line. I used the 10 m DEM within the logan riverscapes project as elevation data. In order to obtain a longitudinal profile, I traced the profile along with the Logan River Only layer in GIS and used the create profile tool. To determine the base level I looked at the attribute table of the profile graph to see where the value leveled off and remained steady. I also visually checked the map (info tool) to confirm these findings.
2. The base-level control of the Logan River 18,000 years ago was 1291 meters where it met Bonneville Lake. After a quick google search, I found that the Logan River once encompassed the entire cache valley. Interesting! I then looked for the area where Bonneville Lake used to be (the salt flats) and found the elevation there. Not the most scientific process, but it gives a general idea.
3. The mainstem of the length of the Logan river is 86.44 kilometers. To get the length of the river I used the summary statistics button within the attribute table. I looked over the attribute table itself to ensure that was the only data being referenced.
4. The concavity of the profile is approximately 0.78. This was calculated using the formula from the text. To calculate concavity my first instinct was to integrate to find the value of A. To reduce the number of steps I drew a straight line from the bottom to the top of the LP. I then determined the midpoint and approximated the value of A. H I calculated H using the total change in elevation from the headwaters to the mouth.
To determine knickpoints I looked at the longitudinal profile above (figure 3) as well as a profile created in google maps. Being unfamiliar with this watershed (I'm in Oregon), I had to do some research about its history. I discovered that there are three dams along the river which explain the larger knickpoint occurring at approximately 50,000 meters downstream of the headwaters. Beginning 20,000 meters downstream of the headwaters the longitudinal profile has a high density of smaller scale knickpoints. These knickpoints appear to occur in the area of the watershed where tributary densities increase.
Catchment Morphometrics
Calculation Methods
To calculate morphometric characteristics I used GIS, google earth, and excel.
Area of Catchment: Determined using the attribute table in GIS and cross-checked using the measurement tool and summary statistics.
Length: To determine the length I used my calculation of catchment area obtained in GIS and the formula given in the book. This calculation is measuring the length of the catchment itself and not the length of the channel. Thus; L=1.4(67.97km^2)^0.6= 67.97
Perimeter: To determine the perimeter of the catchment I added an additional field to the attribute table and calculate geometry.
Circulation ratio: I am not completely confident in this calculation. I was getting very strange values using the formula in the book and other attempts. I found this formula (youtube example problem). This is a very small value, which indicates that the catchment is elongate and controlled by geologic controls.
Elongation ratio: I used previous calculations of area and length to determine this unitless ratio. I calculated a value of 0.42, which indicates a more elongated catchment. These findings agreed with the circulation ratio.
Form Factor: The value of 9.51 that I calculated indicates lower flood intensities.
Catchment Relief: I determined the min and max elevations using my longitudinal profile data.
Relief ratio: I calculated the relief ratio to be 0.02. So the average drop in elevation per "unit length" river is 0.02.
Perennial network length: I calculated this in GIS using summary statistics.
Drainage Density: I calculated this in excel using previously calculated metrics.
Table 1. Catchment morphometric calculation values for the Logan River Watershed
Stream Order
The Logan River Watershed does follow the laws of Hortan network composition, there are a greater number of small order streams than larger order streams, larger order streams seem to be longer than short order streams, and drainage increases as stream order increases.