. DMS : Diagnostic Modeling System. Sedimentation and deposition; Channels (Hydraulic engineering). 100 80 60 O 40 20 k- sta1 Measured Modeled. 252 254 256 258 260 262 264 266 268 270 272 Year Day 1997 Figure 26. Comparison of calculated and measured velocities at sta 1 At sta 2, shown in Figure 27, calculated velocity matched the measured current in phase, but overestimated the peak magnitude by as much as 50 percent during some periods (, YD 253 at 1800). During other periods, such as YD 255 at 0600, the calculated peak velocity matched the measured velocities to within 4 cm/sec. Inspect
. DMS : Diagnostic Modeling System. Sedimentation and deposition; Channels (Hydraulic engineering). 100 80 60 O 40 20 k- sta1 Measured Modeled. 252 254 256 258 260 262 264 266 268 270 272 Year Day 1997 Figure 26. Comparison of calculated and measured velocities at sta 1 At sta 2, shown in Figure 27, calculated velocity matched the measured current in phase, but overestimated the peak magnitude by as much as 50 percent during some periods (, YD 253 at 1800). During other periods, such as YD 255 at 0600, the calculated peak velocity matched the measured velocities to within 4 cm/sec. Inspecting currents at sta 2 together with both the wind directions recorded at the East Matagorda station and the water-surface elevations recorded at the Galveston Pleasure Pier, it appears that the model overestimates water velocity if the wind is blowing in the same direction as the current. For example, the model over-predicts water velocity during ebb flow when the wind is from the north. During periods when the wind direction differs by more than 50 deg from the current direction, the calculated velocities nearly match the measurements. The matching of calculated and measured velocity for these transient wind events is difficult because the current meter measures at a point in the water column, whereas the model calculates an average over a relatively large grid area (approximately 1,000 sq m). A second cause for these discrepancies at sta 2 can be attributed to driving the model with water-surface elevation and wind measured at sites outside the study area. Galveston Pleasure Pier and East Matagorda Bay stations are located about 70 and 20 miles, respectively, to the northeast from the MSC entrance. Given these relatively large distances, the wind-induced setup and setdown contained in the time series of water- surface elevation measured at the Galveston station may not be synchronous with the wind measured at East Matagorda. Thus, the forcing imposed on the model is not synch
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