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. 180-350m) | -12m AHD |
| Jet pump spacing | 30m |
| No. of jet pumps | 11 |
| Maximum number of operational jet pumps at any time | 5 |
| 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 | 655l/s | 14m | KSB Ajax submersible centrifugal pump | Tweed River |
| High pressure pump (1 off) |
745kW | 540l/s | 124m | KSB Ajax centrifugal pump | Control building - ground level |
| Flume dilution pump (1 off) |
20kW | 111 l/s | 13m | KSB Ajax centrifugal pump | Control building - ground level |
| Slurry pumps (2 off) | 473kW | 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 |
| Jet pumps | 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 900,000 m3/yr to 1,200,000 m3/yr |
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.
Last updated: 28 November 2003