CVEN9640 Coastal Engineering Assessment 2 Brief | UNSW

CVEN9640 Assessment Scope-government Brief 

For this assessment you will be introduced to the SBEACH numerical simulation model that is very commonly used by Coastal Engineering consultants, to predict beach, berm and dune erosion during storms. You will also use and interpret data and provide engineering advice to a client. 

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 apartment complex 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 (2025) as well as the years 2050and 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).

Page 2 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. 
• For the purposes of this assignment, the projected sea level rise (SLR) for the region has been adopted as 0.25 m (2050)and 1.0m (2100)compared to present day (2025) mean sea level. You can assume linear changes between now and 2050 and between 2050 and 2100. 
• 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 (D50 ) of beach sand at Narrabeen is 0.32 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) 

IN CLASS DEMONSTRATION 

SBEACH 

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). This year we will run this in class as part of the demonstration! You can choose to also look at the model yourself in your own time, but the output files we generate in class together will be what we use for the analysis.

In pairs or small groups, discuss how well does the calibrated model predict the observed June 2016 storm erosion? This will come in handy when you get to Part B below. 

Run the model for the pre-storm beach profile (termed a 'reach' in SBEACH) using the scenario Narrabeen Profile PF4 June 2016and assess the expected uncertainty in your results based on the existing model calibration that is based on the June 2016storm. 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 2025 file!

In the demonstration we will run both the 2016 storm and the ARI storm for you. Output files will be provided to you in Moodle for further analysis. During this demonstration, work in pairs or groups to consider the following (this part is NOT handed in).

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). 

CVEN9640 PART B: Recommendations to the Client - Written Brief (50 MARKS) 

To be Submitted in Moodle as a single PDF document. The document should be no more than 3 pages in length. 

Combine all your knowledge of the 100yr ARI design storm erosion (Part 2), long-term recession/accretion rate (Part 3) and SLR recession (Part 4) at PF4 to provide your client advice on where the present (2025), 2050 and 2100Coastal Erosion Hazard Lines should be at this location.

Your brief should include the following: 

1. Calculate and explain how you have determined the location of each of these three hazard lines (2025, 2050, 2100). This should include representative equations for EACH of the hazard lines and indicate what of the above components you considered and WHY. (this should be no more than ½ page) 
2. Indicate these three hazard lines on an aerial image (e.g. using a screenshot of Google Earth or other GIS software) in the area of interest. This should be done on 1 (one) clearly labelled figure that takes up about ½ of a page. 
3. Briefly discuss two limitations of the methodology you have used to establish these hazard lines. (2-3 sentences) 
4. Briefly discuss any limitations from the SBeach modelling done in class as part of the demonstration. How well did the model calibrate to the training data done in the workshop? How confident are you in your Storm-demand results? (2-3 sentences)
5. Considering the 2 methods used to determine long term recession at this beach. How similar were they? Which did you choose to use in your hazard calculations and justify why? (2-3 sentences) 
6. Consider the Nielsen et al., 1992paper and the description of the various coastal hazard zone provided (see figure below), including the 'zone of slope adjustment', and 'zone of reduced foundation capacity'. In words, answer the following: if you were building a temporary structure, such as lifeguard tower, what landward extent would you choose to represent your storm demand (ie do you choose the zone of wave impact, zone of slope adjustment, or zone of reduced foundation capacity)? Would your decision change if this was a house on piles? Or for the proposed development described above? Provide 1 sentence for your justification for each of the 3 options (total 3 sentences). 
7. Based on the methods you used above in (1) and your answer to (6) along with the building type being planned, have you included all the necessary setback distances? Why/Why not? 
8. The proposed developer has determined that your company is doing the hazard line assessment for local council and has asked you to reconsider your estimates - they are too conservative in their mind and will mean they can't maximize their profits as they would like to. Referring to the Engineers Australia code of ethics; what should you do, and why?Refer to at least 3 of the dot points in the ethics document as part of your reasoning. 

Additional reference Figure from Nielsen et al. 1992.