Fume Observations
1.) Flume Controls
1.1 Water discharge (Q) is defined as the rate of the volume of water flowing through a river. This can have many impacts on a river, one being how much of the bed load is being transported. 1.2 Slope (S) is the gradient of the river and is the angle of incline or decline; this can determine which erosional and depositional processes occur in a system. 1.3 Sediment discharge (Qs) is the amount of sediment leaving the system; in your experiment, it is the amount of sediment that went out of the plug and was collected in the net. 1.4 The channel profile is the change in elevation for the entire length of the river. A change in base level can change the longitudinal profile of the river drastically. 1.5 The base level of a system is the lowest point in elevation that all of the water flows to. In our experiment, it was represented by raising or lowering the drain plug.
2.) Fluvial Geomorphic Processes
2.1 Bed erosion can be defined as the entrainment of sediment from the bed of the river. It is controlled by how much power the river is exerting and whether that has the ability to move the bed material. 2.2 Bank erosion is when the sides of a river are being chipped away at. This usually occurs on the outside bends of rivers. 2.3 Deposition refers to when there is no longer enough stream power to transport the sediment load and therefore the sediment is deposited in the stream. This often occurs when there is a rise in base level and the river is having to adjust its profile. 2.4 Sediment transport is the river's ability to move sediment downstream. The grain size of sediment determines whether it is more likely to be transported as bed load or suspended load.
3.) Fluvial Geomorphic Mechanisms
3.1 Grain-size sorting occurs because larger grained sediments require more energy to be transported so they will be found in higher energy areas. However, sediments of smaller grain sizes require much less energy and can be found in lower energy areas. 3.2 A meandering river is one that is very sinuous as a result of it being unconfined laterally. They can be found in areas with lower elevation and stream power. 3.3 Braiding occurs in rivers when there are multiple unstable channels and bars that are a result of high sediment transport rates. 3.4 An avulsion is when a river channel switches and forms an entirely new channel. This often happens as a result of structural forcing within the old channel. This can be seen in the flume experiment when vegetation was added to the stream. 3.5 Chute dissection occurs when flow levels drop and the river begins to carve into previously submerged deposits. In the flume experiment, this occurs as seepage. 3.6 Structural forcing is when an object (rock, debris, vegetation, etc.) obstructs the channel and causes a disturbance in the flow path; this often results in an avulsion occurring.
3.7 Meandering Channel in Flume
While we were able to observe meandering in the flume experiment, we were not able to produce a classic single-thread meandering channel in any of the experiments. In order to create a true single-thread channel, the sediment within the flume must have enough cohesive strength (through clay particles or vegetation) to stabilize its banks just enough to allow meandering to occur. However, the sediment in the flume we were using had almost no cohesion and therefore there was no ability for banks to truly stabilize and create a single-thread meandering river.
4.) Events
4.1 A small flood was simulated in the flume by increasing the flow rate. As a result, some of the smaller channels became one large channel in an attempt to keep up with the flow. Also, the sediment transport rate drastically increased during this small flood event. 4.2 We simulated a big flood by building a "dam" and stopping up all the water; eventually, after increasing the flow the dam began to erode until it broke. As a result, water rushed into the basin near the base level and a big flood occurred. 4.3 A channel realignment was simulated by increasing the flow of the river. After doing so, the multiple braided channels in the center of the flume became one straight channel.
4.4 Small vs. Big Flood
Both the small and the big floods managed to turn multiple braided channels into one somewhat straight channel as a result of increased flow in the channel. However, the big flood was able to transport significantly more sediment in comparison to the small flood which can be seen in the previous section (4.1 & 4.2).
4.5 Overbank flows, Bankfull flows and Baseflow flows?
Overbank flow was observed in every video in the event section as well as the avulsion and structural forcing videos. Bankfull flow can be observed in the sediment transport, bed erosion, and braided river videos. In all of these videos, there is rapid sediment and bedload transport and very little lateral channel movement. Baseflow occurs in both the meandering river and deposition videos; in both videos, the low flow rate creates the ability for sediments to be deposited in the system.
4.6 Hyporheic Flow
As a result of the flume having relatively large grain sizes of sediments in relation to the overall channel size, the flume had a large hyporheic zone for its channels. Hyporheic flow can be seen as seepage in the flume experiment and was a large contributing factor to the formation of new channels and avulsions
4.7 Recession Limb Flow
Recession limb flow, which is also referred to as the return from flood conditions to baseflow conditions, can be seen when the large single-channel flood system changes to a sinuous and braided system. This happens because a decrease in discharge means less sediment can be transported; this creates depositional features and leaves an abandoned flood plain.