Content deleted Content added
|
|
|
As discussed in the Manning’s n table above, the main creek n value of 0.20 is considered very high, especially in the lower reaches of the study area. A sensitivity analysis was carried out by lowering all the Manning’s n values in the main channel (modeled as 1D cross-sections) to 0.10.
The image below shows the flood depths and extent of thisfor sensitivitythe casetwo whichnon-infiltration showsimulations someat slight100ft differenceresolution (left with channel 'n' = 0.2, right with channel 'n' = 0.1). Some significant deviations in flood extent whencan comparedbe toobserved, particually soth of the 0main channel.2 This can be largely attributed to the higher conveyance in the channel for the 'n'=0.1 case. <br>
[[File:FMA3_3.jpg|600px]][[File:FMA3_4.jpg|600px]]<br>
The beloweffect figureof provideschannel roughness can also be seen in hydrograph outflows from the model downstream boundary. Of particular interest is that reducing the n value to 0.1 has a significant effect on the arrival time of the flood waters at the model outlet (much earlier), and reduces the volume of water flowing onto the floodplain by around 20% due to the higher conveyance of the creek. Also of interest is that for the n=0.2 scenario, some overbank floodwaters return to the main creek near the model outlet causing a delayed second rise in the outlet flow hydrographs as illustrated in the chart further below. This effect does not occur for the n=0.1 scenario, with all overbank floodwaters remaining on the floodplain.<br>
|