CVEN9640_T12024_Assessment2

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University of New South Wales *

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9640

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Civil Engineering

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Apr 3, 2024

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CRICOS Provider Code 00098G Coastal Engineering – CVEN9640 Assessment 2 2024 ASSESSMENT SCOPE – G OVERNMENT B RIEF For this assessment you will use the SBEACH numerical simulation model that is very commonly used by Coastal Engineering consultants, to predict beach, berm and dune erosion during storms. The assessment is set up as a hypothetical government brief in which you will apply a model to provide engineering advice to your client Dr. Sophie Scamps, MP for Mackeller, Parliament of Australia . You will find it useful to refer to the ‘Beaches, Hazards, Climate Change’ and ‘Cross-shore Sediment Transport’ notes from weeks 3 & 4. The information that you will need to complete the assessment is provided in Moodle, as well as some additional resources that you may find useful; plus any other engineering reports/academic journal papers you may discover online. Ministerial briefs must be short and to the point. Highlighting the points needed to help debate and make decisions. Scenario : A new beachfront restaurant development is proposed at Narrabeen – Collaroy Beach located on Sydney’s Northern Beaches. You have been asked by your client to develop Coastal Hazard lines at the preferred location for a new beachfront development, to assess how far back from the present-day shoreline it should be located. The Minister requires hazard lines for present day (2024) as well as the years 2050 and 2100 so she can discuss these in an upcoming parliamentary session on climate change. For an introduction to the concept of ‘Coastal Hazard Lines’ refer to your ‘Beaches, Hazards, Climate Change’ notes from last week. To complete this assessment, you will also need to carefully read the more detailed publication (available in Moodle) by Nielsen et al. (1992) . Background information (NB: these values change EVERY YR so do not rely on old reports!): • Assume no erosion due to a negative sediment budget and/or beach rotation at this site. • Projected sea level rise (SLR) for the Sydney region has been adopted as 0.2 m (2050) and 0.75m (2100) compared to present day (2024) mean sea level. • The Council has advised that storm erosion demand is to be based on a 100yr ARI (‘average recurrence interval’) storm for Sydney. • The effective grain size (D 50 ) of beach sand at Narrabeen is 0.35 mm. • The latitude/longitude of the origin (i.e. x= 0) of the cross-shore beach profile PF4 where the proposed new building is to located is: ( -33.7171, 151.29970 )

Page 2 INSTALL SBEACH SOFTWARE AND LOAD CALIBRATED PROJECT FILE The model and various help and data files are located within the .zip file “SBEACH 64bit” in Moodle. Note that this model does not run in macOS (refer below). Download, install and run the SBEACH software. Now load the project file (available in Moodle) that has already been calibrated for this site: File à Open… CVEN9640_2024.SB . *** NOTE This file changes every year so make sure you use the 2024 version! ***** If you are unable to install the software on your own PC, SBEACH is also installed on all the PCs located in the School’s computer laboratories on level 2 (room CE201) & level 6 (room CE611) of the Civil & Environmental Engineering Building. You can access these PCs remotely from anywhere in the world using myAccess ( https://www.myaccess.unsw.edu.au/ ) by logging in and choosing ‘Desktops’ at the top and CIVIL-LABPC-H20- Rm611 (Note: if you really want to use a Macbook or iMac for this assessment you will need to install your own Windows shell program before installing SBEACH). ASSESSMENT TASKS *PART 1: How well does the calibrated model predict the observed June 2016 storm erosion? (15 MARKS) Run the model for the pre-storm beach profile (termed a ’reach’ in SBEACH) using the scenario Narrabeen Profile PF4 June 2016 and assess the expected uncertainty in your results based on the existing model calibration that is based on the June 2016 storm. Important: make sure that you do not change any of the parameters in this SBEACH project file for your analysis, as it has already been calibrated for you. Make sure you are using the 2024 file! 1.1) Present a clearly labelled figure that compares both the measured and modelled June 2016 post-storm profiles to the original (measured) pre-storm beach profile. Summarise your calculations and briefly comment of the accuracy of the SBEACH model at predicting: 1.2) the magnitude of subaerial (i.e., above mean sea level: elevation = 0) beach volume change caused by the 2016 storm, and 1.3) the change in beach width. To calculate this use the horizontal change in beach width corresponding to the 0.7 m above MSL contour, which at this site is equivalent to the mean spring high tide water elevation. 1.4) Briefly comment on any key differences between the post-storm observed and predicted surfzone shape (ie below MSL). *PART 2: Estimate the 100yr ARI storm erosion to determine Coastal Hazard lines (20 MARKS) Using the same project file CVEN9640_2024.SB but this time using the scenario 100yr ARI storm Sydney :

Page 3 2.1) Present a clearly labelled figure that compares the modelled 100-year ARI post-storm profile to the 2016 pre-storm measured beach profile. 2.2) Calculate the subaerial (i.e., above 0 m MSL) 100yr ARI storm demand volume at this site. How does this compare to the 250 m 3 /m that is considered the typical storm demand for open coast NSW Beaches? Based on this 100yr ARI subaerial storm demand and the initial June 2016 pre-storm profile, use the approach described in Nielsen et al., 1992 to summarise your calculations of: 2.3) the zone of wave impact (assume an average ground level of 10 m above MSL) 2.4) the zone of slope adjustment (assume an angle of repose of 34 degrees) 2.5) the zone of reduced foundation capacity (assume the depth of scour is 1 m below MSL for an open beach). 2.6) Summarise these results by plotting each of these three zones on a clearly labelled cross-section of the PF4 2016 pre-storm Narrabeen Beach profile. *PART 3: Long-Term Erosion/Accretion Trends (15 MARKS) The data file “ Narrabeen_PF4_BW_1976_2024.xlsx ” (available in Moodle) contains monthly beach width measurements based on the 0.7m contour at the Narrabeen PF4 profile downloaded and processed from http://narrabeen.wrl.unsw.edu.au/ . 3.1) Using this data file, estimate using linear regression the long-term recession or accretion rate corresponding to the 0.7 m contour elevation at this location. Provide your answer in metres/year. 3.2) Compare this rate with an equivalent estimate obtained from the “NSW Beach Profile Database” online tool ( http://www.nswbpd.wrl.unsw.edu.au ). [HINT: Use the “Block 4, Profile 6” contour timeseries and make sure you are using the same elevation]. 3.3) Based on these two estimates, select the most appropriate long-term recession-accretion estimate to use in Part 5 below. Briefly justify your selection based on the likely accuracy of each estimate. *PART 4: Estimate shoreline recession due to projected sea level rise by 2050 and 2075 (20 MARKS) The Bruun Rule (refer to the week 4 notes) can be used to estimate shoreline recession due to future projections of sea level rise (SLR). Berm height B can be estimated from the profile data given in the NSW Beach Profile Database. Depth of closure ( h c ) and active surf zone length ( L ) can be estimated either by equation(s) from your notes or otherwise (state your assumptions). 4.1) Calculate an appropriate depth of closure

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