flooding of comparable magnitudes but shorter durations and thus plugs did not form during these periods. In Figure 4.5 the normal conditions represent periods in which the El Niño index does not exceed 0.5 or fall below -0.5 for more than two months during the year. Therefore, the influence of the El Niño and La Niña periods can be compared individually rather than simply comparing these periods against one another. It appears from Figure 4.5 that the La Niña periods are characterized by a duration of overbank flows that is generally much shorter than the normal conditions and the El Niño periods are characterized by having a longer period of discharge greater than two thousand cubic feet per second than the normal conditions but of comparable periods for discharges greater than three thousand, four thousand, or five thousand cubic feet per second. A possible explanation for the El Niño events having a similar or shorter duration of discharges that are greater than three thousand, four thousand, and five thousand cubic feet per second is due to the presence of dams upstream that prevent large peaks by releasing a greater quantity of water over a longer period of time. Therefore, although the El Niño events typically experience a greater overall discharge during the year, this period is not subjected to longer durations of high discharges. Overall it appears that it is less likely that a relatively long duration of overbank flow will occur during La Niña periods and it is more likely that a relatively long duration of overbank flow will occur during El Niño periods in regions with an overbank discharge of less than approximately three thousand cubic feet per second. Figure 4.4: Average Days per Year with an Average Discharge beyond a Threshold Magnitude between 1986 and 2012 for La Niña, El Niño, and Normal Conditions [Rainwater 2013] : Description of Plug Formation The flow chart as shown in Figure 5.1 below illustrates the process that is believed to produce sediment plugs on the Middle Rio Grande. This process has been categorized into four stages to illustrate this process. The first stage is entitled the causing factors since these factors represent the initial circumstances that enable the resulting effects in stage two. The spring runoff duration and sequence however has been separated from the spring runoff magnitude because it is not expected that this factor contributed to the resulting effects. The spring runoff duration and sequence and the resulting effects are expected to be capable of forming a sediment plug, perching, and avulsion but it would require multiple seasons. However, when combined with
flooding of comparable magnitudes but shorter durations and thus plugs did not form during these periods. In Figure 4.5 the normal conditions represent periods in which the El Niño index does not exceed 0.5 or fall below -0.5 for more than two months during the year. Therefore, the influence of the El Niño and La Niña periods can be compared individually rather than simply comparing these periods against one another. It appears from Figure 4.5 that the La Niña periods are characterized by a duration of overbank flows that is generally much shorter than the normal conditions and the El Niño periods are characterized by having a longer period of discharge greater than two thousand cubic feet per second than the normal conditions but of comparable periods for discharges greater than three thousand, four thousand, or five thousand cubic feet per second. A possible explanation for the El Niño events having a similar or shorter duration of discharges that are greater than three thousand, four thousand, and five thousand cubic feet per second is due to the presence of dams upstream that prevent large peaks by releasing a greater quantity of water over a longer period of time. Therefore, although the El Niño events typically experience a greater overall discharge during the year, this period is not subjected to longer durations of high discharges. Overall it appears that it is less likely that a relatively long duration of overbank flow will occur during La Niña periods and it is more likely that a relatively long duration of overbank flow will occur during El Niño periods in regions with an overbank discharge of less than approximately three thousand cubic feet per second. Figure 4.4: Average Days per Year with an Average Discharge beyond a Threshold Magnitude between 1986 and 2012 for La Niña, El Niño, and Normal Conditions [Rainwater 2013] : Description of Plug Formation The flow chart as shown in Figure 5.1 below illustrates the process that is believed to produce sediment plugs on the Middle Rio Grande. This process has been categorized into four stages to illustrate this process. The first stage is entitled the causing factors since these factors represent the initial circumstances that enable the resulting effects in stage two. The spring runoff duration and sequence however has been separated from the spring runoff magnitude because it is not expected that this factor contributed to the resulting effects. The spring runoff duration and sequence and the resulting effects are expected to be capable of forming a sediment plug, perching, and avulsion but it would require multiple seasons. However, when combined with
USBR%20Final%20Sediment%20Plug%20Report%201-21-2014.docx