Detailed Analysis: Coastal Water Management and Jetty Extension Report

This comprehensive report details the analysis, design, and evaluation of a jetty extension project within the Currumbin Creek area. The study encompasses hydrodynamic research, wave data collection, sediment transport analysis, environmental impact assessment, and coastal structure design. The project aims to improve the area's inlet, reduce sediment transport, and enhance recreational access. The report includes an executive summary, introduction, study area description, environmental conditions analysis, hydrodynamic design considerations, and coastal structure design specifications. The research addresses challenges like limited data availability by using data from a nearby location. The report also highlights limitations and recommends further investigations for more accurate results. The design includes design water depth calculations, MHWS calculations, and an analysis of wave data. The findings and recommendations provide a calculated proposal for improving the conditions of the area.

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COASTAL WATER MANAGEMENT
By (Student’s name)
Tutor’s Name
Institution
City
Date

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EXECUTIVE SUMMARY
A very detailed analysis, creation and evaluation of a jetty extension inside the Currumbin zone
at a tidal inlet that is tiny is outlined in this report. Analysis techniques are as follows;
hydrodynamic research of the place, collection of wave data, the study of sediment transport,
environmental effects, coastal structure design and shoreline evolution. The appendices provide
the required calculations. The investigation results of the place indicate that the current state of
the area is passable, however, it requires certain improvements to be done. The new jetty was
specifically designed in order to minimize the sediment transport in the place and offer access to
recreational amenities to the tourist and residents.
Essentially, the research outlines a calculated and comprehensive proposal that will better the
conditions of the area. A more effective technique has been provided to boost the inlet of the area
and as a result, the latest dredging investment has been replaced. There is a need for the place to
be further monitored and investigated so as to obtain more accurate results.
The following are some of the discussed recommendations:
 The data range should be increased
 More accurate location information should be used
 The sediment transport or the sand-bypass system should be enhanced
Some of the limitations experienced while performing the analysis have also been laid down in
this report. They include:
 There was no time, given that this research requires very long timelines. The research is
required to be very detailed, more methods of design, testing and parameters.
 No available information about the area, hence, the implementation of conditions and
wave information was done using the information of an area closer to it Tweed Head.
Although the costs were a huge challenge but result to be obtained could be more exact
and applicable to the activity to be undertaken.
INTRODUCTION
A natural stream known as Currumbin creek is 24 km long like a river before it connects inside
the Coral Sea. The stream is found in South East Queensland. The local government in Gold
Coast governs the catchment areas which are about 489 kilometres square. History indicates that
Currumbin creek has been altered with over 200 years besides its natural state by use of dredges.
The major influence of these alterations is agricultural and logging activities. Besides the
stream's latest setting and development, it has experienced the late 1950's mining practices which
continued up to the 1980s. Along the sea, the creek has a wall to the south facing the side of the
sea that was built in 1973 so as to aggravate the development of headland and floods. A stable
wall was built in the year 1980 in the northern side.

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Figure 1 above shows Currumbin creek satellite images in different years.
The surrounding waters of the Currumbin creek as well as its natural latest setting is a very
famous place for leisure and recreational activities. The place is popular for boats that move into
the Coral Sea's open waters that pass through the creek's mouth consisting of the Palm Beach
Reef. The creek has a long history of water sports activities which includes the boat-goers,
kayaking, fishermen alkies, jet skiers and surfing. There are the developed residential houses that
are very fine located along the Currumbin creek flowing river that may be used as spaces for
recreation activities such as a recently created grass park and rowing clubs to replace the old club
Palm Beach Bowls. The dredging program manages the Currumbin creek so that the recreational
activities can be sustained. This program improves the quality of water, maintains it, nourishes
the beaches and mitigates the risks of flooding.
Figure 2. a map illustrating the dredge area
This report aims at helping the intervention design for the existing jetty built an extension to
point upward north so as to sustain and enable recreation activities. There are recent factors
which include recreational issues, quick swallowing beach leading to problems in suffers and

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jetties movements. The reasons behind the design of extending the jetty point in order to transit
swiftly into the Coral Sea are also investigated in this report. The report also outlines the
hydrodynamic concerns, environmental issues, maintain the design as well as the coastal site
management in relation to disaster susceptibility (Krishnamurthy et al., 2018).
STUDY AREA
The area research in this report covers a tiny tidal inlet that is located in the South East. Recently
the site is faced with problems associated with movement capacity designed for jetties and the
issue of land drying up is on the rise making it difficult for the jetties to move. Dredging of the
Creek’s entrance is another environmental challenge that requires to be addressed (Griffith
Centre for Coastal Management, 2009). There exists an increase in challenges in keeping the
Creek more effective and remain in operation and open for concerned stakeholders. The design
intends to increase activities in regards to jetties as well as take it further in the sea where
clashing and movements while surfing may not happen in the future.
ENVIRONMENTAL CONDITIONS
In Australia, the largest area that does not gain capital is the Gold Coast, however, the benefits
depend on the long and extensive coastal line created to improve the national hub for recreational
activities such as water sports and the competitions internationally. The development of the
creeks and the coast are among the recreational and tourism assets. In deciding to develop any
work associated with the creation of creeks, for instance, the extension of jetties project
conducted in this report, it requires complete consideration and justification the internal and
external environmental factors. In this design report, the environmental context must consist of
the quantity and quality of water associated with the freshwater fish, quality of sediments, tidal
analysis, ecological conditions, design, riverine discharges, wind and wave considerations and
complexities in their conditions of existence. The current tidal intrusion and the conditions of the
geospatial in relation to Currumbin creek are classified into two different parts namely; estuarine
and freshwater (D’Agata and Tomlinson, 2001).
Quality of water: the creek’s water quality comprises of both the estuary and freshwater sites
according to the conditions of monitoring in existence by the GHD (2004). The creek’s estuarine
upper waters are losing its value in terms of the quality of oxygen retention and turbidity,
whereby, the dissolved nitrogen concentration from the benchmarks is excess. This leads to
contamination of water rendering it harmful for aquatic and human life too. The mouth of the
creek is chocked most of the time because of the accumulated algae exposed closely to the
riverine that are released near the mouth of the creek.
Ecological conditions: in the ecological sense, the Currumbin creek is narrow, has a length of
20kms and a valley that is steep on its sides comprising of the subtropical rainforest of mixed
density. There exists mangrove, rainforests like vegetation, woodland, various seagrass
communities and wet sclerophyll forest. The tidal barrage monitors the tidal wave that is low in
regards to estuarine intrusion.
Quality of sediments: the Ecological Health Monitoring Program performed a survey and the
results indicated that the estuarine sites and freshwater sites sedimentations were in a bad

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condition. The pollution rise was proved to be the reason behind the increased toxic chemical
levels more than the acceptable limits.
The upper flow of the stream: reports have shown the spread of seasonal running of water in
which the months of September and August experienced very low flows noted down. A rise of
up to 60 MGL per day has been experienced and can increase to 880 MGL per day at the time of
rainy seasons. The flow quality has been associated with the distribution of the ecological
aspects. The flow of water has a great impact on the volume of navigation and marine life.
Tidal currents: a very huge intertidal ebb symmetry zone is under development in relation to
the levels of floods. At the most recent extended sites of the jetties points, there is a substantial
increase in the tidal currents recorded above 3m MSL. The demands of these tidal currents are
that the design interventions have been properly constituted to be able to withstand the
perpendicular forces. A lot of information and simulations able to be integrated into design
analysis are required at the time when jetty points are being designed to illustrate workability of
the structure suggested.
HYDRODYNAMIC DESIGN
Currumbin Creek is a tiny tidal inlet found in Australia, South East Queensland ( 28.1270 S,
153.4840 E.) The issues of unsecured navigation via the channel at the entrance and partial
closure sum up the creek’s long maintenance history. The entrance is more famous for surfing
and the place is also heavily used by recreational crafts navigating the ocean. The inlet
management has been rendered more complex due to the conflicts existing between various
stakeholders. Dredging must be conducted annually now that two of the entrance jetties are in
operation since 1981. This is to ensure that the entrance is open to allow access by its various
stakeholders. However, the recent dredging investment has not offered the expected results and
just after the campaign of every dredging, the entrance is faced with navigation difficulties and
indications of shallowness.
This group conducted a detailed research about the place in order to design a structure of the
coast that can help to boost the coastline area. But, the challenge is that there is a lack of
available information about the place. For the research to be conducted, the wave information of
a nearby place, Tweed Head, was applied. The creation of a wave rose plot is done by use of the
collected information to determine the direction of the waves, which have greater effects on the
structure. Applying the function of the rose plot on hydrodynamic analysis software known as
MIKE, the following figure was achieved:

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Figure 3 shows the plot of Wave Rose
Looking at the figure above, one can identify that the significant and predominant height of
waves is originating from the East. There is a 4.5 meters critical height. In this study, its
proposed structure is preferably being situated in the North-North-East. Hence, the propagating
waves in the location of the build are considered.
The data collected for these waves were taken by the government between the years 2012 and
2017 should be inserted by DHI into the MIKE software to gain extreme values. The software
used in the Extreme Value Analysis statistically analyzes and distributes the estimated Peak Over
Threshold input onto values to yield results being looked for. a 5-year wave and input data were
logged in and used. The analyzed software produces Weibull, log-normal distribution and
Generalized Pareto graph that show the extreme heights of waves.
In this paper, a 200-year return period is being used with the consideration of a normal structure
within the maritime at a low hazard degree to property or life, the water height’s extreme value
was approximated at 8.977m as seen in the graph below.

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DESIGN OF COASTAL STRUCTURE
1. Design water depth:
The design water depth = local depth + storm surge + SLR
Due to the Jetty go through the area of local depth 1m and 2 m as shown Figure below:
Figure 5. The bathymetry of the area and proposed extension layout
Therefore, we choose:
The local depth head design: h = 2 (m)
The local depth of trunk design including 2 parts:
- Local depth trunk 1: htrunk1 = 2 m
- Local depth trunk 2: htrunk2 = 1 m
1.1. MHWS (Mean height water springs) calculation
As introduced in class, MHWS is considered as water level h depth for design. In this project,
Queensland Semidiurnal Tidal Planes - 2017 (Queensland Government, 2017) of Tweed
River Breakwater port where is the closest port to Currumbin Creek was referred to
determine design MHWS = 1.47m from the datum for the MSL = 0.91m also form the datum
in the report.
According to the figure above the MSL for design jetty equal 2m for the Head of Jetty and
1m for the Trunk of Jetty
Due to the MHWS is the gap between 1.47m and 0.91m => the gap = 0.56 m
Therefore, in this project MSL ( local dept h )=2 m

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¿> MHWS=0.56+2(local dept h)=2.56 m for head and Trunk (local depth 2m)
¿> MHWS=0.56+1(local dept h)=1.56 m for the Trunk (local depth 1m)
1.2. SLR (Sea Level Rise) Determination:
By referring Table 4.1 and Table 5.4 of AS4997-2005, we are designing this jetty for 100
years as its design life, 500 years as its design wave period and 0.4 (m) SLR.
 SLR: 0.4m.
1.3. Storm Surge:
For this project, we are considering the Yasi Cyclone. As claimed by DERM's Townsville
tide gauge, the setup is about 0.6m above HAT (Highest Astronomical Tide).
Thus, Strom Surge = 0.6m
Overall, the Design water depth:
hdept h 1=2.56+0.4 +0.6=3.56 ( m ) for head and Trunk (local depth 2m)
hdept h 2=1.56+0.4+0. 6=2.56 ( m ) for the Trunk (local depth 1m)
2. Wave Period
By collecting the outcomes from the MIKE software and the wave rose, Hs of 500 return
years was 8.977m.
After knowing the Hs, the wave period Tp can be easily calculated from the formula:
T p=a × Hs
b
After using the Regression method, the developed formula is: T p=9.89236 × H s
0.0773
Putting the values in the above equation, the wave period:
T p=9.89236 × 8.9770.0773=11.7 s
3. Wave Transformation
The wave height at the toe of the structure that is at deep water level can be known by
transferring the wave from the shallow water. It can be done using the phenomenon called
Shoaling (Ks) and Refraction (Kr).
In order to find Hs, we have to find Ks and Kr. Because of Hs =Ks Kr Ho
3.1. Shoaling
This phenomenon is basically the effect of the water waves when they are generating in the
shallow water. In order to find the Shoaling, we used the formula: Ks =¿ ¿ ¿ ¿

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Where k = 2π/L and L ≈ L0 {tan h [ ( 2 π
L × √ h
g ) 3
2
] }
2
3
and Lo=1.56 × Ho
2
Substitute values into the equation above, we get
h (m) Ho (m) Tp (s) k Lo (m) L (m) Ks
3.56 8.977 11.7 0.091631 213.5484 68.57074 1.034573
3.2. Refraction
From the wave Rose as mention above the majority of the wave was from the East direction
Therefore, the angle between the wave crest and local depth contour
Using the following equations to calculate the Refraction Factors Kr:
k r= √ cos θo
cos θ Where: θ=sin−1 ( sin θ0 L/ L0 )
The result for Refraction was shown in the table below:
θ0 0.5061(rad)=29o
θ 0.1563(rad)=8.955o
Kr 0.9410
Finally, the Wave height at Jetty:
Hs =1.034573× 0.941× 8.977=8.73(m)
4. Check breaking conditions:
4.1. For Head and Trunk (local depth 2 m)
The Breaking point in shallow water can be calculated be by:
Hsb=0.095 e4 β Lb tan h ( 2 π hb
LP ,b )
Assume the bed slope ¿ 1 :50=¿ β=0.02

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The results of the breaking wave are shown in the table below:
bed slope (β ¿ hb (m) Lb (m) Hsb (m)
0.02 (1:50) 3.56 68.57074 2.22
Check Breaking:
Hs >H sb ( 8.73 m>2.22 m ) =¿ t h e designwave h eigh t H s=2.22 m
4.2. For the Trunk (local depth 1 m)
bed slope (β ¿ hb (m) Lb (m) Hsb (m)
0.02 (1:50) 2.56 68.57074 1.6256
Check Breaking:
Hs > H sb ( 8.73 m>1.6256 m )=¿ t h e design wave h eigh t H s=1.6256 m
5. Design cross section of Structure:
This project design the Jetty include
3 layers: armour, filter and permeable core layer
The slope of structure: 1:1.5=>tanα=0.667
The design structure was shown in the figure below:
Figure 6. Design Structure
5.1. Size of rock at Trunk (local depth 2 m)
Using Hudson method to calculate the size of amour unit (D50) and the Weight of amour unit
(M50)
H1/ 10
Δ D50
=¿ ¿

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H1 /10 (m) ρs kg /m3 ρw ¿ Δ tanα K D D50 (m) M 50 (kg)
2.82402 2650 1000 1.65 0.667
2 (for trunk
and
breaking)
1.186707 4428.697
As the result: we choose: D50=1.2 m=¿ M 50=4579.2 kg
Trunk’s
layer Factors Weight (Kg) Size (Dn50) (m)
Armour
layer W 4579.2 1.2
Filter layer W/10 457.92 0.557
Core W/200 to W/400 22.896 0.2
Toe W/10 457.92 0.557
5.2. Size of rock at the trunk (local depth 1 m)
H1 /10 (m) ρs kg /m3 ρw ¿ Δ tanα K D D50 (m) M 50 (kg)
2.065 2650 1000 1.65 0.667
2 (for trunk
and
breaking)
0.87 1745
As the result: we choose: D50=0.87 m=¿ M 50=1745 kg
Trunk’s
layer Factors Weight (Kg) Size (Dn50) (m)
Armour
layer W 1750 0.87
Filter layer W/10 175 0.404
Core W/200 8.75 0.15
Toe W/10 175 0.404
5.2. Size of rock at Head
Using Hudson method to calculate the size of amour unit (D50) and the Weight of amour unit
(M50)
H1/ 10
Δ D50
=¿ ¿
H1 /10 (m) ρs kg /m3 ρw ¿ Δ tanα K D D50 (m) M 50 (kg)
2.82402 2650 1000 1.65 0.667 1.6 (for 1.278 5535.87