Overview:
The study section of the Logan River for this assignment is upstream/downstream of the Spring Hollow bridge in Logan Canyon. All observations of the study reach occurred on 1/21/21. This section of the Logan River is confined on the northern side from Highway 89. This confinement disconnects the Logan River from a portion of its floodplain and the eroding sediment from the limestone cliff. It should be noted that there is a remnant channel on the northern side of Highway 89 (Figure 1). Looking upstream from the Spring Hollow bridge the Logan River splits into the main on the left and a back channel on the right. The vegetation of the lowland riparian zone between the two channels consists of grasses, cattails, and a variety of shrubs. There is also a stark contrast between the bed sediment materials of the two channels. The main channel consists of a cobbly material where as the side channel consists of a fine sand alluvial sediment. The slower moving water of the side channel was habitat for trout and suckers, specifically areas within the channel that contained woody debris or deep pockets. The riparian zone around the side channel contained vast amounts of beaver sign from past and present chews as well as tracks. There were multiple springs that actively fed the side channel.
Figure 1: Map of Logan River Study Reach.
Step 1:
Upstream of the Spring Hollow bridge the main channel of the Logan River has a cobble bed in the middle of the river. The southern edge of the main channel is being eroded and the sediment is being deposited on the cobble bed. The land mass between the main channel and the side channel acts as a lowland riparian zone. During floods the riparian zone will allow for additional water storage. The side channel acts as a sediment storage area during floods.
Step 2:
During high flow events the side channel will become reconnected upstream and will decrease flow velocities, but downstream the northern floodplain is disconnected because of Highway 89. This will result in more water within the channel during high flow events and cause erosional processes. Additionally, Highway 89 blocks the Logan River from being able to migrate in that direction so it is expected that over time river processes will begin to erode the southern banks and migrate in that direction.
Step 3:
One major control along the Logan River is the presence of Highway 89. Not only does this affect the direction the channel is able to migrate, but also limits sediment supply within the river. Also downstream the river has been dammed for an agricultural irrigation water source. This changes the natural flow regime and will increase the summer low flows.
Step 4:
The surround topography is a mountainous area that is also a karst environment. The Logan River is spring fed, but also contains a large contributing area. The slope of the Logan River is high around the headwaters and through the Bear River Range of Utah, but once the rive enters Cache Valley the slope decreases, which results in more meandering of the river.
Virtual Presentation of Study Area
https://earth.google.com/earth/rpc/cc/drive?state=%7B%22ids%22%3A%5B%2215gj19x12bcSFBEELEBHvyTAHdvIp8Z47%22%5D%2C%22action%22%3A%22open%22%2C%22userId%22%3A%22100601257196187594359%22%2C%22resourceKeys%22%3A%7B%7D%7D&usp=sharing
Comentarios