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The University of British Columbia Department of Civil Engineering CIVL 417 – COASTAL ENGINEERING PROJECT GUIDELINES & FAQ Updated: November 4, 2023 (Note that updates to this document will be posted on Canvas, as additional questions may arise.) Wind Analysis 1. How should we utilize the wind data record to obtain the 1-hr winds with return periods of 5- years and 50-years? First, note that the wind data record includes a column of times re. PDT or PST. Ignore this column, and rely instead on the year-month-day-time columns (that have been converted to PST). First, based on an aerial view of adjacent fetches via Google Earth, decide on two or three wind directions that you will use in the analysis. These should presumably be reasonably distinct, and should include the longest fetches that are relevant. For any selected wind direction q , retain and rely on wind data for directions q , q + 10º and q – 10º and treat all such data as associated with the wind from the selected direction q . Presumably these directions (remember "from") will be selected between about 40º and 120º. Presumably you will work off the 417refSoln5 spreadsheet to obtain the relevant 1-hour wind speeds. [There is no need to obtain multi-hour wind speeds – instead use the method given under item 2 below.] In preparing the data, you should first delete all data with speeds of less than, say 30 kph; and delete all data for wind directions that are not relevant, thereby obtaining one data set for each selected direction. Please review and follow the notes within the spreadsheet regarding the approach to pasting date/time, speed and direction data. In turn, for each selected wind direction, apply this data to spreadsheet 417refSoln5. This process avoids clustering effects, so that there is eventually one maximum 1-hr wind speed for each storm (defined as being 21 or more days apart). In applying tab 5D (EVA), you only need the top 10 – 20 points to determine the 50-year wind, but you need more points, say 70 – 80 to determine the 1-year wind. Wave Hindcasting 2. What wind duration should we use in the wave hindcast analysis?

You should have obtained 5-year and 50-year 1-hr wind speeds for various directions. For each of these cases, use the following equation to obtain the corresponding 2-hr, 3-hr and 4-hr wind speeds: U(N-hr)/U(1-hr) = 1 – 0.08 × N where N is set to 2, 3 and 4 in turn. Then, for each direction, you can use the spreadsheet 417refSoln6 (hindcasting analysis) for the four durations, and select the wave height and period that are the largest. Tide Levels 3. Why use HHWLT / LLWLT and not HHWMT / LLWMT? First, please note the following terminology HHWLT higher high water large tide – referred to in charts as Large Tide, HHW LLWLT lower low water large tide – referred to in charts as Large Tide, LLW HHWMT higher high water mean tide – referred to in charts as Mean Tide, HHW LLWMT lower low water mean tide – referred to in charts as Mean Tide, LLW You want to know the most severe conditions and these will be associated with the most extreme tide levels, especially since tide levels cause wave direction (and wave length) changes and one of these combinations should lead to the most severe wave penetration into one side of the harbour of the other. Note that the chart indicates that Chart Datum corresponds to LLWLT, so the LLWLT is 0 m CD. [If required, LLWLT relative to GD is available from the CAN-ELWAT portal.] Wave Diffraction Plots 4. Please clarify how many contour plots we should obtain for wave heights within the marina? You should have already obtained sets of incident wave conditions at the marina entrance (i.e. after shoaling and refraction) for both high and low tides, for the two or three directions and for the 5-year return period. Develop one plot (for the entire marina) for the single most severe wave condition for diffraction around the south breakwater and another plot (for the entire marina) for a different single most severe wave condition for diffraction around the north breakwater. (Remember that you need only do this for the 5-year design waves, not the 50-year design waves.) The most severe wave condition will depend on the incident wave height (higher is more severe), the wave period (affecting the wave length, longer is the most severe), either high or low tide (affecting the wave length, longer is more severe), and wave direction (direction more directly into the sheltered area is the most severe). I suggest that you just try out two or three wave conditions with high / low tide, using a diffraction diagram for a typical point in the sheltered area to assess which wave condition is the most severe. And then do your computations with one wave condition only for north breakwater and one for south breakwater.

5. Please describe how to obtain the diffraction coefficients at multiple points within the marina and then plot the corresponding contours ? First, develop a pair of grids as in the sketch below showing multiple points within the marina behind the north and south breakwater (only sketch for north breakwater shown). Then I would suggest using the spreadsheet 417refSoln3A to obtain the diffraction coefficients for the grid points behind each breakwater in turn. [You could do this using the diagrams instead, but that may be more cumbersome.] You will likely need to insert rows within the reference spreadsheet to the extent desired; then “copy down” so that the formulae stay intact; and then adjust the x and y values to suit. This will likely be along the lines shown in the sketch below: Then copy and paste all this into a matrix with, say, the x values in the top row, the y values in the first column and the K d values for the different (x, y) values appearing in the cells. And then convert the K d values to H values (since there are different incident wave heights for each breakwater). You might then plot the contours by eye, or use a contour plotting program. [e.g. CIVL3D, QGIS, or even EXCEL has a crude version of this: go to Chart à Surface.] 6. How do we plot the contours for the less sheltered area between the breakwaters the diffraction coefficients at multiple points within the marina and then plot the corresponding contours ? If you have the contours of wave heights for the sheltered areas behind the north and south breakwater, for the same wave condition, then you might complete the contours by eye (using rough judgement) for the non-sheltered area in between.

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Rubblemound breakwater 7. How should we calculate the rock size for the rubblemound breakwater? For the most severe incident wave condition, use the Hudson and/or Van der Meer approaches. If you use both methods, perhaps then take the rock size to be the higher of these two estimates less one third of the difference between them (i.e. somewhat higher than the average between them). 8. How should we estimate the walkway width and elevation on the south breakwater? Walkway width . Use any non-coastal guidelines, probably the width of two wheelchairs crossing, plus an extra 1 m. Walkway elevation . For the elevation, I would take the following relative to chart datum: HHWLT + Vertical Allowance + maximum wave runup for the 50-year design wave condition + 0.3 m of freeboard. I did not provide information on runup on rubblemound breakwaters in my notes. Please take this to be 0.8 × incident wave height; and don't forget that the maximum incident wave height in a storm is about 1.8 × significant wave height. Tangential Velocity at Caisson Base (540 students) 9. What formulation should we use for the tangential velocity, and how do we compute this on a spreadsheet? The tangential velocity u q at the base of the cylinder may be obtained by differentiating a known expression for the velocity potential f , using : ࠵? ! = % 1 ࠵? ( ࠵?࠵? ࠵?࠵? This leads to the following expression for the time-varying tangential velocity u q along the cylinder surface: % ࠵? ! ࠵?࠵?/࠵?࠵? ( = − 1 cosh (࠵?࠵?) :; ࠵?࠵? " . sin (࠵?࠵?) ࠵?࠵?࠵?࠵? " ($) ! (࠵?࠵?) & "’( B exp (−࠵?࠵?࠵?) Thus the corresponding amplitude of the tangential velocity, denoted U q , is given by: % ࠵? ! ࠵?࠵?/࠵?࠵? ( = − 1 cosh (࠵?࠵?) I; ࠵?࠵? " . sin (࠵?࠵?) ࠵?࠵?࠵?࠵? " ($) ! (࠵?࠵?) & "’( I This is considered analogous to the expression for runup given the text / notes. In order to utilize the above, review the available spreadsheet solution for the runup distribution (as a function of q ), given within 417refSoln7, and adapt this to obtain instead the distribution of

U q (as a function of q ). That is, you will need to modify some of the terms within the spreadsheet, e.g. replacing cos(m q ) by sin(m q ), etc. I suggest that you validate your edits by obtaining the plot and noting that U q should be zero at q = 0º and 180º; and that the maximum value of U q is expected to be of the order of twice the maximum velocity at the seabed due to incident waves alone.

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