Module 3-Coastal Hydraulics Assignment 2020 PDF

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CVEN90051 Civil Hydraulics – 2015

Melbourne School of Engineering

Coastal Hydraulics Assignment Coastal Environment of Port Phillip Bay Weighting (10%)

Due Date: Sunday November 1st, 11:59PM

General Instructions This assignment is to be submitted individually. Overall, the assignment should be equivalent to 2,000 words including calculations where appropriate and it should take no longer than a combined effort of approximately 20 hours. The background information and figures provided should primarily be used, however additionally researched material may be used. All sources must be referenced in-text following an author date format and with a bibliography appended. This assignment consists of four parts. Answer questions chronologically and succinctly, showing simple calculations in text and extended calculations in an appendix. Marks will be equally assigned for correct evaluation of the questions and your conceptual interpretation of results. There is no need to adopt a formal report format. The weighting of each section is shown in the heading to the section, and will be marked accordingly. Although each section is marked independently, later questions require reflection on your responses to earlier ones. Submission will be made electronically via Canvas. Late assignments will have marks deducted. Any form of plagiarism is unacceptable and will be dealt with in accordance with the University’s ‘Academic Honesty and Plagiarism Policy’ (https://academicintegrity.unimelb.edu.au/).

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CVEN90051 Civil Hydraulics – 2015

Melbourne School of Engineering

Background Information Port Phillip Bay (shown in Figure 1) covers a surface area of 1950 Km2 and is relatively shallow, with more than half the bay having a depth less than 8 m (DPI, 2010). The 5, 10, 15 and 20 m bathymetric contours are also shown in Figure 1. Figure 2 shows . It also shows the tidal levels at Williamstown (Near Melbourne’s CBD) at the most northern extent of Port Phillip Bay. The stretch of water connecting Port Philip Bay with Bass Strait is relatively narrow and often shallow, with its bathymetry shown in Figure 3.

Figure 1: Bathymetric chart of Port Philip bay showing the locations of Port Phillip Heads and Williamstown where the tides shown in Figure 1 were recorded (DPI Victoria, 2010: Fish in our waters).

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CVEN90051 Civil Hydraulics – 2015

Melbourne School of Engineering

1.6

1.4

SWL (m)

1.2

1

0.8

0.6

0.4

0.2 0

24

48

72

Figure 2: Diurnal Tidal Variation at Port Philip Heads and Williamstown between 17-19 July, 2012 (BoM, 2012)

The entrance of the channel connecting Port Phillip Bay with Bass Strait has become known as ‘The Rip,’ because of the large currents observed. Recent dredging works have been undertaken to ensure the passage of large ships through the channel, which is of great navigational significance. The channel and the location of these dredging works have been shown in Figure 3.

Figure 3: Bathymetric chart of Nepean Bay Bar in 1836 [Holdgate et al., Australian Journal of Earth Sciences (2011) 58, (157–175) from (DCNR, 1995)] Page 3

CVEN90051 Civil Hydraulics – 2015

Melbourne School of Engineering

Part 1: Offshore Processes (10%) There are a number of tools for wave-forecasting available online. The service provides by www.windy.com is based on the global model that is operated by the European Centre for MediumRange Weather Forecasts. To access the service for the region around Melbourne directly, click on the following link: https://www.windy.com/?-37.741,145.001,5 . There are a number of options on the righthand side that would let you explore different layers (parameters). Make sure that wind sea and swell options are selected. Using windy to assist you, focus on the marine forecast for Bass Strait to get a close-up view of the processes nearby the entrance of Port Philip Bay and Portsea. Answer the following questions. a) Briefly state the difference in sea and swell waves being produced by windy. b) List reasons why waves inside Port Phillip Bay differ significantly in magnitude compared with offshore sea state. Particularly, discuss i. How wave properties change as waves propagate around Port Philip Heads ii. What factors influence the generation of waves inside Port Philip Bay (Note – as these questions depends on the specific day you consider, make sure to add some figures showing the wave conditions outside and inside the bay in support to your answers)

Part 2: Surf-zone Processes (40%) Assume a deep-water significant wave height of 20m, significant period of period of 15s and a wave direction of 240 degrees (coming from) a) What is the breaker wave height and direction of propagation in front of the Nepean Peninsula at depths of 10, 5 and 2.5m? b) Would breaker wave height and direction of propagation be the same when approaching the beach at Point Lonsdale (the western side of Port Philip Heads)? c) Assuming a beach slope of 10% for Nepean Peninsula (ocean side) and 5% for Port Lonsdale, what kind of breaking waves would dominate at these two locations? d) What is the magnitude of the setup at the shoreline at these two locations? e) What longshore processes do you expect will occur along Point Nepean and Point Lonsdale? Provide calculations to support your answer. f)

Based on your findings, do you believe wave-induced surf-zone processes impact on sand deposition in Port Philip Heads (“The Rip”)? Can these surf-zone process affect navigation? Can you propose a solution? Justify your response with reference to theory.

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CVEN90051 Civil Hydraulics – 2015

Melbourne School of Engineering

Part 3: Tides (30%) Using the supplied information and Figures 1-3, answer the following questions (show full working in calculations and assumptions made): a) What is the average tidal propagation speed between Port Philip Head and Williamstown? b) Calculate (stating assumptions made) the tidal prism and maximum current magnitude between Point Lonsdale and Point Nepean. You will need to select a suitable cross section at the channel entrance. c) What other factors impact on the magnitude of the current? How could the offshore bathymetry further increase the magnitude of the current? d) Do you believe this current is capable of maintaining an open channel, making reference to your answer to 2f)? Do you believe that dredging is justified? (Hint: revisit the theoretical concepts you learnt in the Natural Channels Module Topic 6)

Part 4: Weather and Climate (20%) a) Consider the scenarios of a major low-pressure system (“East Coast low”) in Bass Strait, which induces a surge of 1m. With reference to your answers in Question 2 and 3d, what impact would this have on the surf-zone processes on Point Nepean, Point Lonsdale and Port Phillip Heads. Would there be risk of closure of Port Philip? b) Considering the whole environmental condition (waves, tides, storm surges, etc…), over what time scales would the surf-zone processes occur? In this context, do you think dredging is a viable option in the long term to maintain maritime traffic through Port Philip heads? Would there be other options to ensure navigation?

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