Measuring quantities pumped ashore
There are two factors to take into account when estimating the quantity of sand reaching the beach. The amount we claim as pumped ashore is recorded by the dredger and we have to allow for a “bulking factor” of 1.2 due to the material being mixed with water in the hopper. For instance, if we’re told that 3,000 cu.m. has been pumped from the hopper it would equate to 2,500 cu.m. actual material dredged.
We then allow for an estimated 20% of that 2,500 cu.m. being lost to the foreshore during pumping, so only 2,000 cu.m. might be left on the beach.
These figures provide guidelines. Beaches are independently surveyed on a daily basis, comparing levels and widths to a baseline survey carried out before work commenced, and in that way we get a far more accurate idea of how much sand has actually been delivered.
Poole beach replenishment
The Poole replenishment programme included beaches between Shore Road and Branksome Dene Chine, using two dredgers – the Ham 311 and Waterway.
The sinkerline first came ashore just east of Branksome Chine on 15th December 2005. It was moved to Canford Cliffs Chine on 7th January and the final dredger load of sand was pumped to Shore Road at 19:30 on 16th January. The eventual length of the onshore pipeline leading from Canford Cliffs to Shore Road was 2,306m.
Poole beaches were due to receive approximately 450,000 m³ of new sand; the 590,364 m³ recorded as pumped ashore allows for various factors (find out more). A daily independent survey measured amounts retained on the beach.
|Poole Beaches||Days||Loads||Cubic metres||Metric tonnes*||Tons|
|Total pumped ashore||32||226||590,364||885,546||871,560|
|Measured on the beach by independent survey||-||434,950||652,425||642,120|
*The Crown Estate apply a factor of 1.5 to convert cubic metres of sand to metric tonnes, and 1 metric tonne = 0.984206528 long (British) ton.
About the Project
The aim of the new beach is to protect properties and infrastructure from coastal erosion but it will also improve the amenity for residents and visitors.
Project progress was recorded in a Daily Diary
Before & After Replenishment pictures
The finishing touches
- When the beach at Poole had settled down it became necessary to extend the Branksome Chine stream outfall where it discharges at Branksome Chine beach. The flows through the outfall originate from the stream and surrounding surface water drainage system. Flow volume increases rapidly during heavy rainfall and the outfall needs to be able to take the water out to sea. The outfall was 50m long, constructed from an 800mm diameter steel pipeline encased in concrete, supported on both sides by interlocking steel sheet piles and buried beneath the sand. A special license for the work was granted by Defra and an extra 48m of pipe was laid in June 2006.
- For safety reasons we also ‘topped’ the groynes where they protruded above the sand. They were cut down to approximately 6-9″ below sand level and work was completed in June.