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<br />5
<br />Conclusions
<br />The wind-generated wave characteristics and the
<br />related wind setup and wave runup on a sloping
<br />embankment within a reservoir must be considered for
<br />the purposes of designing embankments and
<br />embankment slope protection. Slope protection for
<br />the embankment must also be considered and a
<br />procedure for the design of riprap slope protection is
<br />described in the following article titled, “Design of
<br />Riprap for Slope Protection against Wave Action.”
<br />NOAA Climatological Data Links
<br />Local Climatological Data:
<br />http://www.ncdc.noaa.gov/IPS/lcd/lcd.html
<br />Climate Maps of the United States:
<br />http://cdo.ncdc.noaa.gov/cgi-bin/climaps/climaps.pl
<br />NOAA Climate Data Online:
<br />http://www.ncdc.noaa.gov/cdo-web/
<br />References (with Links where available)
<br /> USDA (1983), Technical Release No. 69: “Riprap for Slope Protection
<br />against Wave Action.”
<br /> Reclamation (1992), ACER Technical Memorandum No. 2: “Freeboard
<br />Criteria and Guidelines for Computing Freeboard Allowances for
<br />Storage Dams.”
<br /> Reclamation (1987), Design of Small Dams, Third Edition.
<br /> USACE (1976), Engineering Technical Letter No. 1110-2-221: “Wave
<br />Runup and Wind Setup on Reservoir Embankments.”
<br /> Saville, Thorndike J. (1954), “The Effect of Fetch Width on Wave
<br />Generation,” Technical Memorandum No. 70, Beach Erosion Board,
<br />USACE.
<br />Example #1:
<br />Find the wind setup, the wave height and the wave
<br />runup of a reservoir as shown on Figure 1. The
<br />observed fastest mile wind speed is 75 mph for this
<br />site. The average depth of the reservoir is 10 feet, and
<br />the riprap protected embankment has a 3H:1V or 18°
<br />slope.
<br />Calculations:
<br />1. To measure the lengths of the central (longest)
<br />and radial lines as shown in Figure 1, compute the
<br />effective fetch using Equation 1. The computation
<br />is shown in Table 2.
<br />
<br />
<br />
<br />
<br />Table 2: Procedure to determine the effective fetch
<br />Radial
<br />No.
<br />Radial Length
<br />(mi), Xi
<br />α
<br />(Degree) cos α Xi·cos2 α
<br />1 1.7 42 0.74 0.96
<br />2 1.8 36 0.81 1.20
<br />3 1.9 30 0.87 1.45
<br />4 2.0 24 0.91 1.70
<br />5 2.2 18 0.95 2.02
<br />6 2.3 12 0.98 2.23
<br />7 2.4 6 0.99 2.41
<br />8 2.6 0 1.00 2.63
<br />9 2.5 6 0.99 2.51
<br />10 2.4 12 0.98 2.33
<br />11 2.3 18 0.95 2.11
<br />12 2.1 24 0.91 1.78
<br />13 2.0 30 0.87 1.53
<br />14 1.8 36 0.81 1.20
<br />15 1.7 42 0.74 0.96
<br /> Sum= 13.51 27.02
<br /> ∑( )
<br />∑( )
<br />
<br /> miles
<br />This effective fetch of 2.0 miles or 10,560 feet
<br />from the given reservoir with a longest fetch of
<br />2.6 miles is estimated.
<br />2. Refer to Figure 5 of TR-69 or Table 1 in this article,
<br />the generalized maximum wind speed-duration
<br />relationship is plotted as the red line on Figure 5.
<br />This is computed by using the observed fastest
<br />mile wind speed, 75 mph, interpolating the ratio
<br />of land wind speed to the fastest mile wind for
<br />each of the durations shown and then multiplying
<br />this ratio by the observed fastest wind speed. The
<br />results of these computations are shown in Table
<br />2.
<br />Table 2: Maximum Wind Speed-Duration Relationship
<br />for a Fastest Mile Wind of 75 mph
<br /> 1 min 30 min 60 min 100 min
<br />Interpolated Ratio
<br />from Table 1 100% 59% 53% 49%
<br />Corresponding Max.
<br />Wind Speed (mph) 75 44 40 37
<br />3. By using Equation 2 and the effective fetch, 2.0
<br />miles, the relationship of overland wind speed-
<br />duration for the selected fetch is determined for a
<br />range of selected speeds (in this case, UL= 90
<br />mph, 60 mph, and 35 mph). Remember to first
<br />convert UL to ft/sec and fetch length to feet. T is
<br />calculated in seconds with Equation 2 and then
<br />converted to minutes for the plot. The results are
<br />shown as the blue curve in Figure 5.
<br />