Technical information

System capacity

Peak sand transport capacity

625m³/hr

1,000 tonnes/hr

Nominal sand transport capacity

500m³/hr

800 tonnes/hr

Average annual capacity

500,000m³

800,000 tonnes

Note: Operations are typically carried out at night.

 

Jetty details

Length

450m

Distance from the Tweed River's southern breakwater

250m

Deck elevation (Ch.168-450m)

+8m AHD

Pile depth (Ch.360-450m)

-23m AHD

Pile depth (Ch.180-350m)

-20m AHD

Pile spacing

10m

Jet pump depth (Ch. 360-450m)

-15m AHD

Jet pump depth (Ch. 280-350m)

-14m AHD

Jet pump depth (Ch. 180 – 270m)

-12m AHD

Jet pump spacing

30m

No. of jet pumps

10

Maximum number of operational jet pumps at any time

4

Slope of slurry return pipe (flume)

2.5 %

Structure material

Steel

Deck material

Concrete

Note: AHD - Australian Height Datum is approximately equal to mean sea level Ch. - Chainage along the length of jetty

 

Pump details

Pump

Power

Flow

Head

Type

Location

Low pressure pump
(1 off plus a spare)

125kW

146kW

655l/s

14m

KSB Ajax submersible centrifugal pump

Tweed River

High pressure pump (1 off)

1100Kw

540l/s

124m

Weir Uniglide centrifugal pump

Control building - ground level

High pressure pump
(1 off spare)

1100kW

540l/s

124m

KSB Ajax centrifugal pump

Control building - ground level

Flume dilution pump
(1 off)

20kW

30kW

111 l/s

13m

KSB Ajax centrifugal pump

Control building - ground level

Slurry pumps (2 off)

473kW

630kW

395l/s

63m

KSB Ajax centrifugal pump

Control building - lower level

Note: The low pressure pump supplies clean sea water from the Tweed River to the high pressure pump and the flume dilution pump. The high pressure pump drives the jet pumps. Slurry (sand & sea water) is delivered by the jet pumps and flows in the flume to the slurry pit, adjacent to the control building. The slurry pumps are then used to pump the slurry under the Tweed River, delivering sand to one of the outlets.

 

Pipeline details

From

To

Length

Diameter

Conveyance

Type

Low pressure pump

Control building

440m

450mm

Sea water

Polyethylene

High pressure pump

Jet pumps

450m (max.)

600>500>400 mm

Sea water

Steel

Flume dilution pump

Flume @
Ch. 390

390m

250mm

Sea water

Steel

Flume

Ch. 450 –Ch. 390

60m

250mm

Slurry

Polyurethane lines steel

Flume

Ch. 420 – Ch. 390

30m

250mm

Slurry

Polyurethane lined steel

Flume

Ch. 390 – Slurry Pit

390m

600mm

Slurry

Polyurethane lined steel

      

Control building

Snapper Rocks East

1210m

400mm

Slurry

Polyurethane lined steel

Control building

Duranbah

1260m

400mm

Slurry

Polyurethane lined steel > Polyethylene

Control building

Snapper Rocks West

2108m

400mm

Slurry

Polyurethane lined steel

Control building

Kirra Groyne

2635m

400mm

Slurry

Polyurethane lined steel > Polyethylene

 

Site conditions

Wave climate
(based on recorded wave data offshore from Letitia Spit in approximately 25m of water since January 1995)

Average significant wave height Hs = 1.3m
Maximum wave height Hmax = 13.1m (recorded on 3/5/1996)
Over 90 % of significant wave heights occur in the range Hs = 0.6m - 2.4m
Average zero crossing wave period Tz = 6.0s
Average peak spectral period Tp = 9.3s
Over 90 % of peak spectral wave periods occur in the range Tp = 5s - 13s
Swell waves occur predominantly from the east to south east sectors.

Tides

Mean High Water Spring = 0.65m AHD
Mean Water Level = -0.01m AHD
Mean Low Water Springs = -0.67m AHD

Water temp

Maximum = 26° C
Average = 19° C
Minimum = 15° C

Sand properties

d90 = 580µm
d50 = 270µm
d10 = 150µm

Longshore transport

Annual Average Gross Transport = 800,000 m3/yr
Annual Average Net Northerly transport = 500,000 m3/yr
The net northerly transport can range from 250,000 m3/yr to 1,000,000 m3/yr, dependent on sea conditions.

 

Design

The principal consultant involved in the design of the permanent bypassing system was Cardno MBK (Qld) Pty Ltd. A number of specialist design consultants were also engaged:

Mechanical Design Services

K Little Engineering Pty Ltd

Coastal Engineering Services

Coastal Engineering Solutions Pty Ltd

Electrical Design Services

J & P Richardson Pty Ltd

Cathodic Protection Services

Corrosion Protection Services Pty Ltd

Design philosophy was to provide design solutions which:

  • Are the most cost effective in terms of construction and operation
  • Address the safety risks associated with construction and operation of the facility
  • Minimise any adverse environmental impact of the facility and
  • Optimise the quality and performance of the facility.

The design life of the sand bypassing system is 50 years.

Page last updated/reviewed: 24 Feb 2015