About Bournemouth's Beach Improvement Schemes (BIS)
Bournemouth beach loses approximately 70,000 m³ of material annually (1 million m³ every 13 years). Since the predominant direction of longshore drift in Poole Bay is from west to east, sand gradually moves along the beaches of Southbourne and Hengistbury Head, and beyond into Christchurch Bay.
The shoreline has been replenished on several occasions in recent years; these projects are referred to as 'Beach Improvement Schemes' (BIS).
BIS2 & BIS3 represented a "boom & bust" approach to replenishment schemes, where the beach was delivered with a large quantity of material (i.e. 1974/75) and left until much of it was lost before funding was available for further replenishment (i.e. 1988/89). From 2005 funding allowed for a change of approach, with BIS4 delivering a 5-year phased replenishment, from 2008-2010 making good annual losses that kept the beach at a constant level and volume until 2012. Replenishment schemes at Bournemouth now form part of the wider Bournemouth Beach Management Scheme 2015-2032, with projects planned every five years.
|BIS4.3-4.5||2008-10 annual top-ups||228,000|
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.
Bournemouth beach replenishment (BIS4.1)
Work on Bournemouth’s fourth Beach Improvement Scheme (BIS4) started on 18th January 2006 at Double Dykes, Hengistbury Head and moved westwards, finishing east of Boscombe Pier on 18th March.
Bournemouth beaches were due to receive approximately 600,000 m³ of new sand; the 726,101 m³ recorded as pumped ashore allows for various factors (find out more).
|Bournemouth (BIS4.1)||Days||Loads||Cubic metres*||Metric tonnes*||Tons*|
|Total pumped ashore||60||290||726,101||1,089,152||1,071,950|
*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 beach material used on Bournemouth’s beaches was selected to match that naturally occurring on the beaches, i.e. a sand & shingle mix at Double Dykes and getting progressively sandier towards Boscombe.
Two dredgers operated – Ham 311 and Waterway until 9th February when Waterway left, bound for Rotterdam. HAM 311 completed the project, and in the early hours of Sunday morning, 18th March, she too departed Poole Bay for Rotterdam.
Project progress was recorded in a Daily Diary
A second contract to complete Bournemouth’s beaches during winter 2006/07 will replenish from Boscombe Pier westwards to the boundary with Poole, using beach material dredged from a Licensed Dredging Area to the east of the Isle of Wight.