TWEED RIVER ENTRANCE SAND BYPASSING ...
TWEED RIVER ENTRANCE SAND BYPASSING PROJECT Overview of Project Activities Background – A Historical Perspective The project is located on a high wave energy coast with substantial movement of sand along the coastline under the action of waves and currents. Various studies have estimated the scale of alongshore sand movement along this section of coast to be in the order of a net long-term average rate of about 500,000 m3 per year to the north. The rate of net northward longshore sand movement varies considerably during the year and also from year to year, with an estimated range of about 250,000 to 1,200,000 m3 per year depending on wave conditions. The natural northward movement of large volumes of sand along the coast at the Tweed River entrance has historically caused navigation problems for commercial and recreational vessels using the river entrance. Shallow offshore sandbars build up at river mouths that are subject to littoral drift as part of the process that allows sand to move across the entrance in its transport along the coastline. The Tweed River training walls were extended in the early 1960s providing deeper navigation depths and safer crossing conditions for only a limited period. By the 1970s, the offshore bar had redeveloped to an extent that navigation was again difficult under certain conditions. Over the next two decades sand continued to accumulate on the Tweed bar and entrance navigation conditions further deteriorated. By 1995, water depths over the crest of the bar were reduced to about 2 metres at low water and waves would frequently break across the bar and create unpredictable, dangerous crossing conditions at the entrance to the river.
Photo 1 Wave Break Across the Tweed River Entrance Prior to Stage 1 Dredging Works
The extension of the Tweed River training walls also interrupted the natural northward supply of coastal sand to the southern Queensland beaches. These beaches were severely eroded by a series of cyclones and ocean storms that occurred in the late 1960s and early 1970s. The reduced natural sand supply hindered beach recovery and contributed to ongoing beach erosion. Rock seawalls were constructed along the southern Gold Coast beaches in the early 1970s to protect foreshore amenities and property from continued erosion. Rock groynes were also constructed at the western end of Coolangatta and Kirra beaches in an effort to trap and retain sand to restore beach amenity. Sand placement campaigns were carried out in the mid 1970s and mid to late 1980s using sand taken from the Tweed River and offshore sources to nourish the eroded upper beaches. By the mid 1990s, the northward reworking of nourishment sand and ongoing reduction in the natural sand supply contributed to a residual sand deficit along the southern Gold Coast beaches compared to the conditions observed prior to the construction of the Tweed River training walls. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Photo 2 Eroded Kirra Beach March 1995, immediately prior to Stage 1 Beach Nourishment Works looking towards Miles St. groyne along the rock seawall constructed in the early 1970’s to protect the foreshore from ongoing beach erosion
Introduction The Tweed River Entrance Sand Bypassing Project (TRESBP) is a joint initiative of the State Governments of New South Wales and Queensland which was set up to improve and maintain navigation conditions at the Tweed River entrance and to replenish and maintain a regular sand supply to the southern Gold Coast Beaches. The project has been carried out in two stages: •
Stage 1 Initial Dredging and Nourishment.
•
Stage 2 Permanent Sand Bypassing System.
In December 1999, the Governments awarded contracts to a consortium led by the McConnell Dowell Corporation Limited for the construction and 23 year operation and maintenance of the Stage 2 Permanent Sand Bypassing System for the Tweed River entrance. McConnell Dowell Constructors (Aust) Pty Limited commenced construction of the permanent system in February 2000. The completed system was commissioned during March and April 2001. The Tweed River Entrance Sand Bypassing Company (a subsidiary company of the McConnell Dowell Corporation Limited) commenced full-scale operation of the permanent sand bypassing system on 4 May 2001. The project is being managed by a Working Group made up of officers from the NSW Department of Lands, the Queensland Environmental Protection Agency (QEPA), the Gold Coast City Council and Tweed Shire Council. The work is coordinated by the Department of Lands.
TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Stage 1 Initial Dredging and Nourishment Works About 3 Million m3 of sand was dredged from the entrance bar and used to restore the southern beaches of the Gold Coast over the period April 1995 to May 1998. Stage 1 was undertaken in two separate phases known as Stage 1A and Stage 1B. Stage 1A Stage 1A works were carried out by Dredeco Pty Ltd under contract to the NSW/QLD Governments over the period 26 April 1995 to 20 August 1996. A total of about 2¼ million m3 of sand was dredged from the Tweed River entrance and placed along the southern Gold Coast beaches (see Table 1). Table 1 : Summary of Stage 1A Dredging and Nourishment Campaigns Period
Placement Volume (m3)
26 April to 2 June 1995
1,518,356
3 May to 19 November 1995
165,593
Krankeloon
7 January to 28 February 1996
261,478
Krankeloon
22 July to 20 August 1996
301,715
Total Stage 1A
2,247,142
Dredge Pearl River Ngamotu
Stage 1A Placement Areas are shown in Figure 1 and the distribution of sand placement summarised in Table 2 (see Figure 2 for details). Table 2 : Summary of Stage 1A Nourishment Volumes Placement Area
Nourishment Volume (m3)
Rainbow Bay Upper Beach
57,984
Greenmount Headland Upper Beach
40,101
Coolangatta / Greenmount Upper Beach
197,702
Kirra Point to North Kirra Upper Beach
294,869
Inner Nearshore
286,358
Outer Nearshore
1,315,435
Snapper Rocks Extension Total
TRESBP Overview of Project Activities, Revision 6, Jan. 06
54,693 2,247,142
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Stage 1B Stage 1B dredging and nourishment works were undertaken by McQuade Marine Pty Ltd (under contract to the NSW/QLD Governments) using the Port Frederick, a 50m long hopper dredge with a load capacity of about 400 m3 of sand. These works commenced on 20 September 1997 and were completed on 26 May 1998. Stage 1B involved the dredging of about 800,000 m3 of sand from the Tweed River entrance area and placement along the inshore and nearshore placement areas from Snappers Rocks to North Kirra. Stage 1B Placement areas are shown in Figures 3 and 4. The distribution of sand placement is shown in Table 3. Table 3 : Summary of Stage 1B Nourishment Volumes Placement Area
Nourishment Volume (m3)
Snapper Rocks Inner Nearshore
314,500
Snapper Rocks Centre Nearshore
85,000
Rainbow Bay Upper Beach
10,000
Coolangatta / Greenmount Upper Beach
1,000
Eastern Inner Nearshore
185,500
Centre Nearshore
11,500
Central Kirra to North Kirra Upper Beach
30,000
Western Inner Nearshore
163,000
Total
TRESBP Overview of Project Activities, Revision 6, Jan. 06
800,500
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Figure 1
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Figure 2
STAGE1A 1A STAGE TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Figure 3
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Figure 4
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Description of the Stage 2 Permanent Sand Bypassing System The sand collection component of the permanent sand bypassing system comprises a sand collection jetty, pumps and control building at the northern end of Letitia Spit, about 250m south of the southern Tweed River breakwater (refer to Figures 5 & 6). The jetty is approximately 450m long and extends into ocean water depths of about 5 metres. The purpose of the jetty-based system is to collect as much as possible of the net northerly moving coastal sand before it reaches and accumulates in the Tweed River entrance, thereby maintaining a clear navigational channel at the entrance. Eleven submerged jet pumps have been suspended from the jetty structure and sunk into the beach and seabed. Operation of the pumps forms a trough in the sand bed beneath the jetty to form a sand trap. Waves and currents continuously feed sand into the jetty sand trap from the ongoing drift of sand along the coast. Sand collected from the sand trap by the jet pumps is discharged through a 400mm diameter buried pipeline to feed beaches north of the entrance. The sand delivery pipeline crosses under the Tweed River about 250m downstream of Jack Evans Boatharbour (refer to Fig. 6).
Figure 5 Tweed River Entrance looking south and showing the sand collection jetty under construction and entrance dredging activity
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Figure 6
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Figure 7
Locality Plan
The system infrastructure also includes: • a clean water low pressure pump station mounted on a short jetty on the southern river training wall at the northern end of Letitia Spit, and • a compound area at the landward end of the sand collection jetty for the housing of a control building and workshop, and sand slurry collection pit (refer to Figures 5 & 7). The jetty system has been designed to capture and deliver on average 500,000 m³ of sand each year under normal operation and has the reserve capacity to deliver at higher rates to clear the jetty sand trap during events such as short-term storms. The majority of sand collected by the jetty system will be delivered to the primary placement area of Snapper Rocks East. To provide flexibility to sand delivery by the system, discharge outlets have also been established at Duranbah Beach, Snapper Rocks West and Kirra Point. The pipeline layout includes provision for future potential sand delivery to the Tweed River lower estuary shoals and Greenmount Beach. The jetty system by itself, may not be able to completely intercept the movement of sand along the beach, nor maintain a clear navigation channel all of the time. Outflanking of the jetty system during severe ocean storms and flooding in the Tweed River may deposit sand in the entrance area and compromise navigation conditions at times. Therefore the contract agreements make provision for the Tweed River Entrance Sand Bypassing Company to undertake supplementary dredging and nourishment works to clear the Tweed River entrance should this become necessary. Dredging would be typically carried out using a trailer suction hopper dredge. The dredge would deposit this sand in the nearshore zone in placement areas from Duranbah Beach to Coolangatta Beach. Dredging campaigns would typically remove and deposit in the order of 200,000 to 300,000 m³ of sand. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Operation of the Permanent Sand Bypassing System Sand Collection and Delivery by the Jetty-based Sand Bypassing System Construction of the jetty-based sand bypassing system commenced in February 2000. The system was officially commissioned at the beginning of May 2001 and full-scale operation commenced on 4 May 2001. This followed two months of intensive commissioning trials to test the capability and performance of the facility. During the commissioning period, the system pumped a total of 185,664 m3 of sand to the Snapper Rocks East and Duranbah Beach outlets. Sand collection and delivery is generally undertaken at night, to minimise public safety risks and disruptions to the community. Sand is delivered to each outlet by the Tweed River Entrance Sand Bypassing Company, in accordance with the sand delivery program developed by the Governments in consultation with the project’s community Advisory Committee. Quantities pumped to each of the sand delivery outlets are summarised in Table 4: TABLE 4
Summary of Stage 2 Sand Pumping Volumes, (4 May 2001 to 31 December 2005) Year 2001
Quantity of Sand Delivered (m3)
(4 May to 31 December)
390,205
2002
(1 January to 31 December)
721,364
2003
(1 January to 31 December)
787,026
2004
(1 January to 31 December)
496,367
2005
(1 January to 31 December)
724,931
Total
3,119,893
Delivery Outlet
Quantity of Sand Delivered (m3)
Duranbah
266,174
Snapper Rocks East
2,556,090
Snapper Rocks West (trial delivery)
1,586
Kirra Point
264,112
Greenmount Beach
31,931
Total
3,119,893
Approximately 80% of the sand quantity delivered by the jetty-based sand bypassing system was pumped to the primary Snapper Rocks East outlet. This sand was transported naturally by ocean waves and currents away from the outlet and around Snapper Rocks headland, to feed the beaches to the north west of Snapper Rocks. About 10% of the total sand delivery was pumped to Duranbah Beach to nourish the upper beach which had been badly eroded by ocean storms. During late 2000 and early 2001, Coolangatta and Greenmount Beaches accreted significantly while beaches to the north of Kirra Beach eroded. About 264,000 m3 of sand has been pumped to the Kirra Point outlet provide a more immediate supply of sand to the beaches to the north of Kirra Point to improve beach and surfing amenity. A small quantity of sand was also pumped to the Snapper Rocks West outlet near the end of October 2001 to test the Snapper Rocks West sand delivery pipeline. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Stage 2 Dredging and Nourishment Works Pre-Commissioning Remedial Dredging and Nourishment Works Tweed River entrance dredging and southern Gold Coast beach nourishment works were carried out to improve navigation and beach amenity conditions during construction and commissioning of the jetty-based sand bypassing system. McQuade Marine No. 2 Pty. Ltd., under subcontract to McConnell Dowell Constructors (Aust.) Pty Ltd, undertook the work using the ‘Port Frederick’, a 50 metre long trailer suction hopper dredge. These works commenced on 1 April 2000 and were completed on 29 April 2001. During this period, a total of 532,517 m³ of sand were dredged from the offshore bar at the Tweed River entrance to achieve a Clear Navigation Channel. The majority of the dredged sand was placed in the primary nearshore placement area east of Snapper Rocks (ie 324,567 m³ of sand). The other portion of dredged sand was evenly deposited across the inner, centre and outer nearshore placement areas west of Snapper Rocks to offshore of Coolangatta Beach in water depths of about 4 to 10 metres to develop a regular nearshore nourishment profile (ie 207,950 m³ of sand).
1.4.2.2 Supplementary Maintenance Dredging and Nourishment Works While pre-commissioning dredging achieved a Clear Navigation Channel through the Tweed River entrance offshore bar, these dredging activities were not able to completely remove the offshore bar because of ongoing high sand transport conditions moving sand into the entrance area. At the commencement of sand bypassing system operation, relatively shallow entrance shoals were present on the northern and southern sides of the Clear Navigation Channel. Supplementary dredging and nourishment works were carried out to reduce the entrance shoals and widen the Clear Navigation Channel during the initial operation of the jettybased sand bypassing system while the system developed a beach sand trap in the vicinity of the jetty. McQuade Marine No. 2 Pty. Ltd. were subcontracted by the Tweed River Entrance Sand Bypassing Company to undertake the supplementary entrance dredging and southern Gold Coast beach nourishment works. These works were again carried out using the ‘Port Frederick’ hopper dredge over five campaigns with a combined dredging and placement of about 1,107,000 m3 of sand (see Table 5). All of this dredged sand was deposited in the inner, centre and outer nearshore placement areas from Duranbah to offshore of Coolangatta Beach in water depths of about 4 to 12 metres. Care was taken to distribute this sand across this area to a design that was compatible with good surfing conditions. The distribution of sand placement is shown in Table 6 (i). Table 5 : Summary of Stage 2 Supplementary Dredging and Nourishment Campaigns Supplementary Campaign
Period
Placement Volume (m3)
1
11 May to 6 November 2001
289,971
2
20 May to 20 October 2002
240,129
3a
7 February to 11 March 2003
47,695
3b
13 June to 28 September 2003
183,197
4
7 July to 30 September 2004
169,926
5
22 May to 30 September 2005
176,189
Sub-Total
1,107,107
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1.4.3
Summary of Sand Quantities Delivered by the Project
A summary of sand quantities delivered to the various placement areas since April 2000 by the Stage 2 Permanent Sand Bypassing System is presented in Table 6. The project’s Stage 1 and Stage 2 works removed a total of approximately 8 Million m³ of sand from the vicinity of the Tweed River entrance over the period April 1995 to December 2005. This sand was used to nourish Duranbah Beach and the southern Gold Coast Beaches. These works have improved entrance navigability and beach amenity, built-up nearshore shoals to promote more consistent surfing amenity and reduced storm erosion hazard to foreshore development. The volume of the southern Gold Coast Beaches (ie. Point Danger to North Kirra Beach) have increased by a net amount of about 4.4 Million m³ of sand as at July 2005, as a result of sand nourishment by the project. The remainder of the nourishment sand has been reworked alongshore to feed the eroded beaches to the north.
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TABLE 6 Sand Quantities Delivered to Each Placement Area by the Stage 2 Permanent Sand Bypassing System to 31 December 2005 (i)
Operation Stage Sand Delivery : 4 May 2001 to 31 December 2005 (cubic metres) Pumping by the Jetty-based System Sand Delivery Outlet
Total Pumping
Duranbah
Snapper Rocks East
Snapper Rocks West
Kirra Point
Greenmount Beach
266,174
2,556,090
1,586
264,112
31,931
(ii)
Dredge Deposition
3,119,893
Dredge Placement Area
Duranbah
Snapper Rocks East
Snapper Rocks West
Inner Nearshore
Centre Nearshore
Outer Nearshore Reserve
58,608
513,559
149,106
63,919
81,873
240,042
Total Deliver
1,107,107
4,227,000
Pre-Commissioning Sand Delivery : 1 April 2000 to 3 May 2001 (cubic metres) Pumping by the Jetty-based System Sand Delivery Outlet
Dredge Deposition Total Pumping
Duranbah
Snapper Rocks East
Snapper Rocks West
Kirra Point
Greenmount Beach
21,680
163,984
0
0
0
(iii)
Total Dredge Deposition
185,664
Dredge Placement Area
Duranbah
Snapper Rocks East
Snapper Rocks West
Inner Nearshore
Centre Nearshore
Outer Nearshore Reserve
0
246,987
15,509
30,279
106,531
133,211
Total Dredge Deposition
Total Deliver
532,517
718,181
Total Sand Delivery by the Stage 2 Permanent Sand Bypassing System : 1 April 2000 to 31 December 2005 (cubic metres) Pumping by the Jetty-based System
Maintenance Dredging
Total Delivery
3,305,557
1,639,624
4,945,181
TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Photo 1 Wave Break Across the Tweed River Entrance Prior to Stage 1 Dredging Works
The extension of the Tweed River training walls also interrupted the natural northward supply of coastal sand to the southern Queensland beaches. These beaches were severely eroded by a series of cyclones and ocean storms that occurred in the late 1960s and early 1970s. The reduced natural sand supply hindered beach recovery and contributed to ongoing beach erosion. Rock seawalls were constructed along the southern Gold Coast beaches in the early 1970s to protect foreshore amenities and property from continued erosion. Rock groynes were also constructed at the western end of Coolangatta and Kirra beaches in an effort to trap and retain sand to restore beach amenity. Sand placement campaigns were carried out in the mid 1970s and mid to late 1980s using sand taken from the Tweed River and offshore sources to nourish the eroded upper beaches. By the mid 1990s, the northward reworking of nourishment sand and ongoing reduction in the natural sand supply contributed to a residual sand deficit along the southern Gold Coast beaches compared to the conditions observed prior to the construction of the Tweed River training walls. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Photo 2 Eroded Kirra Beach March 1995, immediately prior to Stage 1 Beach Nourishment Works looking towards Miles St. groyne along the rock seawall constructed in the early 1970’s to protect the foreshore from ongoing beach erosion
Introduction The Tweed River Entrance Sand Bypassing Project (TRESBP) is a joint initiative of the State Governments of New South Wales and Queensland which was set up to improve and maintain navigation conditions at the Tweed River entrance and to replenish and maintain a regular sand supply to the southern Gold Coast Beaches. The project has been carried out in two stages: •
Stage 1 Initial Dredging and Nourishment.
•
Stage 2 Permanent Sand Bypassing System.
In December 1999, the Governments awarded contracts to a consortium led by the McConnell Dowell Corporation Limited for the construction and 23 year operation and maintenance of the Stage 2 Permanent Sand Bypassing System for the Tweed River entrance. McConnell Dowell Constructors (Aust) Pty Limited commenced construction of the permanent system in February 2000. The completed system was commissioned during March and April 2001. The Tweed River Entrance Sand Bypassing Company (a subsidiary company of the McConnell Dowell Corporation Limited) commenced full-scale operation of the permanent sand bypassing system on 4 May 2001. The project is being managed by a Working Group made up of officers from the NSW Department of Lands, the Queensland Environmental Protection Agency (QEPA), the Gold Coast City Council and Tweed Shire Council. The work is coordinated by the Department of Lands.
TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Stage 1 Initial Dredging and Nourishment Works About 3 Million m3 of sand was dredged from the entrance bar and used to restore the southern beaches of the Gold Coast over the period April 1995 to May 1998. Stage 1 was undertaken in two separate phases known as Stage 1A and Stage 1B. Stage 1A Stage 1A works were carried out by Dredeco Pty Ltd under contract to the NSW/QLD Governments over the period 26 April 1995 to 20 August 1996. A total of about 2¼ million m3 of sand was dredged from the Tweed River entrance and placed along the southern Gold Coast beaches (see Table 1). Table 1 : Summary of Stage 1A Dredging and Nourishment Campaigns Period
Placement Volume (m3)
26 April to 2 June 1995
1,518,356
3 May to 19 November 1995
165,593
Krankeloon
7 January to 28 February 1996
261,478
Krankeloon
22 July to 20 August 1996
301,715
Total Stage 1A
2,247,142
Dredge Pearl River Ngamotu
Stage 1A Placement Areas are shown in Figure 1 and the distribution of sand placement summarised in Table 2 (see Figure 2 for details). Table 2 : Summary of Stage 1A Nourishment Volumes Placement Area
Nourishment Volume (m3)
Rainbow Bay Upper Beach
57,984
Greenmount Headland Upper Beach
40,101
Coolangatta / Greenmount Upper Beach
197,702
Kirra Point to North Kirra Upper Beach
294,869
Inner Nearshore
286,358
Outer Nearshore
1,315,435
Snapper Rocks Extension Total
TRESBP Overview of Project Activities, Revision 6, Jan. 06
54,693 2,247,142
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Stage 1B Stage 1B dredging and nourishment works were undertaken by McQuade Marine Pty Ltd (under contract to the NSW/QLD Governments) using the Port Frederick, a 50m long hopper dredge with a load capacity of about 400 m3 of sand. These works commenced on 20 September 1997 and were completed on 26 May 1998. Stage 1B involved the dredging of about 800,000 m3 of sand from the Tweed River entrance area and placement along the inshore and nearshore placement areas from Snappers Rocks to North Kirra. Stage 1B Placement areas are shown in Figures 3 and 4. The distribution of sand placement is shown in Table 3. Table 3 : Summary of Stage 1B Nourishment Volumes Placement Area
Nourishment Volume (m3)
Snapper Rocks Inner Nearshore
314,500
Snapper Rocks Centre Nearshore
85,000
Rainbow Bay Upper Beach
10,000
Coolangatta / Greenmount Upper Beach
1,000
Eastern Inner Nearshore
185,500
Centre Nearshore
11,500
Central Kirra to North Kirra Upper Beach
30,000
Western Inner Nearshore
163,000
Total
TRESBP Overview of Project Activities, Revision 6, Jan. 06
800,500
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Figure 1
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Figure 2
STAGE1A 1A STAGE TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Figure 3
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Figure 4
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Description of the Stage 2 Permanent Sand Bypassing System The sand collection component of the permanent sand bypassing system comprises a sand collection jetty, pumps and control building at the northern end of Letitia Spit, about 250m south of the southern Tweed River breakwater (refer to Figures 5 & 6). The jetty is approximately 450m long and extends into ocean water depths of about 5 metres. The purpose of the jetty-based system is to collect as much as possible of the net northerly moving coastal sand before it reaches and accumulates in the Tweed River entrance, thereby maintaining a clear navigational channel at the entrance. Eleven submerged jet pumps have been suspended from the jetty structure and sunk into the beach and seabed. Operation of the pumps forms a trough in the sand bed beneath the jetty to form a sand trap. Waves and currents continuously feed sand into the jetty sand trap from the ongoing drift of sand along the coast. Sand collected from the sand trap by the jet pumps is discharged through a 400mm diameter buried pipeline to feed beaches north of the entrance. The sand delivery pipeline crosses under the Tweed River about 250m downstream of Jack Evans Boatharbour (refer to Fig. 6).
Figure 5 Tweed River Entrance looking south and showing the sand collection jetty under construction and entrance dredging activity
TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Figure 6
TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Figure 7
Locality Plan
The system infrastructure also includes: • a clean water low pressure pump station mounted on a short jetty on the southern river training wall at the northern end of Letitia Spit, and • a compound area at the landward end of the sand collection jetty for the housing of a control building and workshop, and sand slurry collection pit (refer to Figures 5 & 7). The jetty system has been designed to capture and deliver on average 500,000 m³ of sand each year under normal operation and has the reserve capacity to deliver at higher rates to clear the jetty sand trap during events such as short-term storms. The majority of sand collected by the jetty system will be delivered to the primary placement area of Snapper Rocks East. To provide flexibility to sand delivery by the system, discharge outlets have also been established at Duranbah Beach, Snapper Rocks West and Kirra Point. The pipeline layout includes provision for future potential sand delivery to the Tweed River lower estuary shoals and Greenmount Beach. The jetty system by itself, may not be able to completely intercept the movement of sand along the beach, nor maintain a clear navigation channel all of the time. Outflanking of the jetty system during severe ocean storms and flooding in the Tweed River may deposit sand in the entrance area and compromise navigation conditions at times. Therefore the contract agreements make provision for the Tweed River Entrance Sand Bypassing Company to undertake supplementary dredging and nourishment works to clear the Tweed River entrance should this become necessary. Dredging would be typically carried out using a trailer suction hopper dredge. The dredge would deposit this sand in the nearshore zone in placement areas from Duranbah Beach to Coolangatta Beach. Dredging campaigns would typically remove and deposit in the order of 200,000 to 300,000 m³ of sand. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Operation of the Permanent Sand Bypassing System Sand Collection and Delivery by the Jetty-based Sand Bypassing System Construction of the jetty-based sand bypassing system commenced in February 2000. The system was officially commissioned at the beginning of May 2001 and full-scale operation commenced on 4 May 2001. This followed two months of intensive commissioning trials to test the capability and performance of the facility. During the commissioning period, the system pumped a total of 185,664 m3 of sand to the Snapper Rocks East and Duranbah Beach outlets. Sand collection and delivery is generally undertaken at night, to minimise public safety risks and disruptions to the community. Sand is delivered to each outlet by the Tweed River Entrance Sand Bypassing Company, in accordance with the sand delivery program developed by the Governments in consultation with the project’s community Advisory Committee. Quantities pumped to each of the sand delivery outlets are summarised in Table 4: TABLE 4
Summary of Stage 2 Sand Pumping Volumes, (4 May 2001 to 31 December 2005) Year 2001
Quantity of Sand Delivered (m3)
(4 May to 31 December)
390,205
2002
(1 January to 31 December)
721,364
2003
(1 January to 31 December)
787,026
2004
(1 January to 31 December)
496,367
2005
(1 January to 31 December)
724,931
Total
3,119,893
Delivery Outlet
Quantity of Sand Delivered (m3)
Duranbah
266,174
Snapper Rocks East
2,556,090
Snapper Rocks West (trial delivery)
1,586
Kirra Point
264,112
Greenmount Beach
31,931
Total
3,119,893
Approximately 80% of the sand quantity delivered by the jetty-based sand bypassing system was pumped to the primary Snapper Rocks East outlet. This sand was transported naturally by ocean waves and currents away from the outlet and around Snapper Rocks headland, to feed the beaches to the north west of Snapper Rocks. About 10% of the total sand delivery was pumped to Duranbah Beach to nourish the upper beach which had been badly eroded by ocean storms. During late 2000 and early 2001, Coolangatta and Greenmount Beaches accreted significantly while beaches to the north of Kirra Beach eroded. About 264,000 m3 of sand has been pumped to the Kirra Point outlet provide a more immediate supply of sand to the beaches to the north of Kirra Point to improve beach and surfing amenity. A small quantity of sand was also pumped to the Snapper Rocks West outlet near the end of October 2001 to test the Snapper Rocks West sand delivery pipeline. TRESBP Overview of Project Activities, Revision 6, Jan. 06
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Stage 2 Dredging and Nourishment Works Pre-Commissioning Remedial Dredging and Nourishment Works Tweed River entrance dredging and southern Gold Coast beach nourishment works were carried out to improve navigation and beach amenity conditions during construction and commissioning of the jetty-based sand bypassing system. McQuade Marine No. 2 Pty. Ltd., under subcontract to McConnell Dowell Constructors (Aust.) Pty Ltd, undertook the work using the ‘Port Frederick’, a 50 metre long trailer suction hopper dredge. These works commenced on 1 April 2000 and were completed on 29 April 2001. During this period, a total of 532,517 m³ of sand were dredged from the offshore bar at the Tweed River entrance to achieve a Clear Navigation Channel. The majority of the dredged sand was placed in the primary nearshore placement area east of Snapper Rocks (ie 324,567 m³ of sand). The other portion of dredged sand was evenly deposited across the inner, centre and outer nearshore placement areas west of Snapper Rocks to offshore of Coolangatta Beach in water depths of about 4 to 10 metres to develop a regular nearshore nourishment profile (ie 207,950 m³ of sand).
1.4.2.2 Supplementary Maintenance Dredging and Nourishment Works While pre-commissioning dredging achieved a Clear Navigation Channel through the Tweed River entrance offshore bar, these dredging activities were not able to completely remove the offshore bar because of ongoing high sand transport conditions moving sand into the entrance area. At the commencement of sand bypassing system operation, relatively shallow entrance shoals were present on the northern and southern sides of the Clear Navigation Channel. Supplementary dredging and nourishment works were carried out to reduce the entrance shoals and widen the Clear Navigation Channel during the initial operation of the jettybased sand bypassing system while the system developed a beach sand trap in the vicinity of the jetty. McQuade Marine No. 2 Pty. Ltd. were subcontracted by the Tweed River Entrance Sand Bypassing Company to undertake the supplementary entrance dredging and southern Gold Coast beach nourishment works. These works were again carried out using the ‘Port Frederick’ hopper dredge over five campaigns with a combined dredging and placement of about 1,107,000 m3 of sand (see Table 5). All of this dredged sand was deposited in the inner, centre and outer nearshore placement areas from Duranbah to offshore of Coolangatta Beach in water depths of about 4 to 12 metres. Care was taken to distribute this sand across this area to a design that was compatible with good surfing conditions. The distribution of sand placement is shown in Table 6 (i). Table 5 : Summary of Stage 2 Supplementary Dredging and Nourishment Campaigns Supplementary Campaign
Period
Placement Volume (m3)
1
11 May to 6 November 2001
289,971
2
20 May to 20 October 2002
240,129
3a
7 February to 11 March 2003
47,695
3b
13 June to 28 September 2003
183,197
4
7 July to 30 September 2004
169,926
5
22 May to 30 September 2005
176,189
Sub-Total
1,107,107
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1.4.3
Summary of Sand Quantities Delivered by the Project
A summary of sand quantities delivered to the various placement areas since April 2000 by the Stage 2 Permanent Sand Bypassing System is presented in Table 6. The project’s Stage 1 and Stage 2 works removed a total of approximately 8 Million m³ of sand from the vicinity of the Tweed River entrance over the period April 1995 to December 2005. This sand was used to nourish Duranbah Beach and the southern Gold Coast Beaches. These works have improved entrance navigability and beach amenity, built-up nearshore shoals to promote more consistent surfing amenity and reduced storm erosion hazard to foreshore development. The volume of the southern Gold Coast Beaches (ie. Point Danger to North Kirra Beach) have increased by a net amount of about 4.4 Million m³ of sand as at July 2005, as a result of sand nourishment by the project. The remainder of the nourishment sand has been reworked alongshore to feed the eroded beaches to the north.
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TABLE 6 Sand Quantities Delivered to Each Placement Area by the Stage 2 Permanent Sand Bypassing System to 31 December 2005 (i)
Operation Stage Sand Delivery : 4 May 2001 to 31 December 2005 (cubic metres) Pumping by the Jetty-based System Sand Delivery Outlet
Total Pumping
Duranbah
Snapper Rocks East
Snapper Rocks West
Kirra Point
Greenmount Beach
266,174
2,556,090
1,586
264,112
31,931
(ii)
Dredge Deposition
3,119,893
Dredge Placement Area
Duranbah
Snapper Rocks East
Snapper Rocks West
Inner Nearshore
Centre Nearshore
Outer Nearshore Reserve
58,608
513,559
149,106
63,919
81,873
240,042
Total Deliver
1,107,107
4,227,000
Pre-Commissioning Sand Delivery : 1 April 2000 to 3 May 2001 (cubic metres) Pumping by the Jetty-based System Sand Delivery Outlet
Dredge Deposition Total Pumping
Duranbah
Snapper Rocks East
Snapper Rocks West
Kirra Point
Greenmount Beach
21,680
163,984
0
0
0
(iii)
Total Dredge Deposition
185,664
Dredge Placement Area
Duranbah
Snapper Rocks East
Snapper Rocks West
Inner Nearshore
Centre Nearshore
Outer Nearshore Reserve
0
246,987
15,509
30,279
106,531
133,211
Total Dredge Deposition
Total Deliver
532,517
718,181
Total Sand Delivery by the Stage 2 Permanent Sand Bypassing System : 1 April 2000 to 31 December 2005 (cubic metres) Pumping by the Jetty-based System
Maintenance Dredging
Total Delivery
3,305,557
1,639,624
4,945,181
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