Technical information

SYSTEM CAPACITY

Peak sand transport capacity (pumping)

625 m³/hr

1,000 tonnes/hr

Average annual delivery (pumping and dredging)

500,000 m³

800,000 tonnes

Note: Pumping operations are typically carried out at night but may also occur during the day when conditions warrant.

JETTY DETAILS

Length

450 m

Distance from the Tweed River's southern breakwater

250 m

Deck elevation (Ch. 168–450 m)

+8.3 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 (JP7-10)

−15 m AHD

Jet pump depth (JP2-6)

−12 m AHD

Jet pump depth (JP1)

−6 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.

PUMP DETAILS

Pump

Power

Flow

Head

Type

Location

Low pressure pump
(1 plus a spare)

150 kW

655 l/s

14.4 m

KSB Ajax submersible centrifugal pump

Tweed River

High pressure pump (1)

966 Kw

540 l/s

124 m

KSB centrifugal

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)

477 kW

627 kW

395 l/s

62.5 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

The total underground pipe network length is 4.2km. This consists of polyurethane lined steel and medium density polyethylene pipeline in diameters ranging from 400mm to 560mm.

SITE CONDITIONS

Wave climate
(based on recorded wave data offshore from Letitia Spit in approximately 25 m 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 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 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.