from the dam. Similarly to the reduction in peak flows, this aggradation would serve to reduce the channel slope as shown in Figure 5.3 below. Figure 5.2: Lane’s Balance Influence of Slope Figure 5.3: Zones of Erosion, Transport, and Deposition 2013] 2013] [Rainwater [Rainwater (Equation 5.1) 5.1.3 Floods and Droughts A process resulting from a cycle of droughts and floods may contribute to channel aggradation because of a low sediment transport capacity during drought periods and then due to overbank flow during flood periods. During drought periods the channel filling with sediment leads to reduced bank height. Then when the next peak flow occurs, more flow goes overbank than otherwise would if there was not a deposition of bed sediments during drought. Evidence of plug formation following periods of drought is shown in Figure 4.1a-d. A process resulting from a cycle of droughts and floods that contributes to low bank height, variations in the channel width, and channel perching is shown in Figure 5.4 below. Figure 5.4: Flood and Drought Influence on Channel Geometry [Rainwater 2013] 5.1.4 High Sediment Supply and Low Transport Capacity A high sediment concentration may be a consequence of overbank flow that contains a relatively small amount of sediment and therefore a disproportionately large amount of sediment remains in the channel. Also, a low transport capacity may be a result of a low flow velocity, geometric factors such as a relatively flat slope or a large width-depth ratio, or an increase in the channel roughness. Overbank flow may also contribute to a large width-depth ratio as illustrated in Figure 5.4 as well as a low flow velocity since the flow with the highest velocity is located near the surface of the channel and therefore overbank flow selectively removes the flow with the greatest transport capacity. 5.1.5 Spring Runoff Magnitude, Duration, and Sequence The spring runoff discharge must exceed the overbank discharge in order for overbank flows to occur during this period. In addition to the spring runoff magnitude, a short-term
from the dam. Similarly to the reduction in peak flows, this aggradation would serve to reduce the channel slope as shown in Figure 5.3 below. Figure 5.2: Lane’s Balance Influence of Slope [Rainwater 2013] Figure 5.3: Zones of Erosion, Transport, and Deposition [Rainwater 2013] (Equation 5.1) 5.1.3 Floods and Droughts A process resulting from a cycle of droughts and floods may contribute to channel aggradation because of a low sediment transport capacity during drought periods and then due to overbank flow during flood periods. During drought periods the channel filling with sediment leads to reduced bank height. Then when the next peak flow occurs, more flow goes overbank than otherwise would if there was not a deposition of bed sediments during drought. Evidence of plug formation following periods of drought is shown in Figure 4.1a-d. A process resulting from a cycle of droughts and floods that contributes to low bank height, variations in the channel width, and channel perching is shown in Figure 5.4 below. Figure 5.4: Flood and Drought Influence on Channel Geometry [Rainwater 2013] 5.1.4 High Sediment Supply and Low Transport Capacity A high sediment concentration may be a consequence of overbank flow that contains a relatively small amount of sediment and therefore a disproportionately large amount of sediment remains in the channel. Also, a low transport capacity may be a result of a low flow velocity, geometric factors such as a relatively flat slope or a large width-depth ratio, or an increase in the channel roughness. Overbank flow may also contribute to a large width-depth ratio as illustrated in Figure 5.4 as well as a low flow velocity since the flow with the highest velocity is located near the surface of the channel and therefore overbank flow selectively removes the flow with the greatest transport capacity. 5.1.5 Spring Runoff Magnitude, Duration, and Sequence The spring runoff discharge must exceed the overbank discharge in order for overbank flows to occur during this period. In addition to the spring runoff magnitude, a short-term
USBR%20Final%20Sediment%20Plug%20Report%201-21-2014.docx