DWR_2801666 - Laserfiche WebLink

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