Technical information

SYSTEM CAPACITY

Peak sand transport capacity

625 m³/hr

1,000 tonnes/hr

Nominal sand transport capacity

500 m³/hr

800 tonnes/hr

Average annual capacity

500,000 m³

800,000 tonnes

Note: Operations are typically carried out at night.

JETTY DETAILS

Length

450 m

Distance from the Tweed River's southern breakwater

250 m

Deck elevation (Ch. 168–450 m)

+8 m AHD

Pile depth (Ch. 360–450 m)

−23 m AHD

Pile depth (Ch. 180–350 m)

−20 m AHD

Pile spacing

10 m

Jet pump depth (Ch. 360–450 m)

−15 m AHD

Jet pump depth (Ch. 280–350 m)

−14 m AHD

Jet pump depth (Ch. 180–270m)

−12 m AHD

Jet pump spacing

30 m

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 plus a spare)

125 kW

146 kW

655 l/s

14 m

KSB Ajax submersible centrifugal pump

Tweed River

High pressure pump (1)

1100 Kw

540 l/s

124 m

Weir Uniglide centrifugal pump

Control building – ground level

High pressure pump
(1 spare)

1100 kW

540 l/s

124 m

KSB Ajax centrifugal pump

Control building – ground level

Flume dilution pump
(1)

20 kW

30 kW

111 l/s

13 m

KSB Ajax centrifugal pump

Control building – ground level

Slurry pumps (2)

473 kW

630 kW

395 l/s

63 m

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

440 m

450 mm

Sea water

Polyethylene

High pressure pump

Jet pumps

450 m (max.)

600>500>400 mm

Sea water

Steel

Flume dilution pump

Flume @
Ch. 390

390 m

250 mm

Sea water

Steel

Flume

Ch. 450 – Ch. 390

60 m

250 mm

Slurry

Polyurethane lined steel

Flume

Ch. 420 – Ch. 390

30 m

250 mm

Slurry

Polyurethane lined steel

Flume

Ch. 390 – Slurry Pit

390 m

600 mm

Slurry

Polyurethane lined steel

      

Control building

Snapper Rocks East

1,210 m

400 mm

Slurry

Polyurethane lined steel

Control building

Duranbah

1,260 m

400 mm

Slurry

Polyurethane lined steel > Polyethylene

Control building

Snapper Rocks West

2,108 m

400 mm

Slurry

Polyurethane lined steel

Control building

Kirra Groyne

2,635 m

400 mm

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 = 1.3 m
Maximum wave height Hmax = 13.1 m (recorded on 03/05/1996)
Over 90% of significant wave heights occur in the range Hs = 0.6 m–2.4 m
Average zero crossing wave period Tz = 6.0 s
Average peak spectral period Tp = 9.3 s
Over 90% of peak spectral wave periods occur in the range Tp = 5–13 s
Swell waves occur predominantly from the east to south east sectors.

Tides

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

Water temperature

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

Sand properties

d90 = 580 µm
d50 = 270 µm
d10 = 150 µm

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

The 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.

The bypassing system was constructed by McConnell Dowell Constructions Pty Ltd. and completed in early 2001.