DIVE PLAN FOR A DIVE IN NORTH WALES
THE NATURE TRAIL  (UNDER THE MENAI SUSPENSION BRIDGE)
Sunday 10th April 2022
Organised by
Chris Heywood

Please note
This dive should be suitable for BSAC Sports divers and above.

There are no facilities (Toilets, shops etc) at this site (these may be available in the village/town centre 5 minutes’ walk away.
There are no air filling stations on the island so you will need to bring a full tank/tanks with you.
Due to the currents and tides at this location if you are not ready (i.e., sat on the rocks, kit on and buddy check done) when the dive manager tells you to procced you will not be allowed to dive.
This site can be dived in most weather conditions but winds from a northerly direction stir up the sand around Puffin Island and reduce water visibility in the straights.

Contents

• Directions
• Dive site description
• Dive plan
• Buddy pairs
• Kit list
• Dive management slate
• General diving risk assessment
• Addendum to risk assessment for Rib

Directions
M56
Leave the M6 at junction 20A, then bear right onto the M56
Signposted N. Wales, Chester, Runcorn

Chester Service Area (ROAD CHEF)
Keep in right hand lanes at junction 15 and continue forward
Signposted North Wales, Queensferry

A494 Continue forward onto the A494
Queensferry Bridge

A55 Continue forward onto the A55
Conwy Tunnel
Penmaenmawr Tunnels
At Junction 16 roundabout take the 2nd exit onto the A55
Signposted Bangor

Pen-y-Clip Tunnels

At Junction 15 roundabout take the 2nd exit onto the A55
Signposted Bangor

A487 Leave the A55 at junction 9, then at roundabout take the 1st exit onto the A487
Signposted Bangor

At roundabout take the 2nd exit onto the A487
Signposted Bangor

A5 At roundabout take the 1st exit onto the A5
Signposted Menai Bridge

Menai Bridge

A545 At roundabout take the 2nd exit onto the A545
Signposted Beaumaris
Turn right after Post Office on right
Follow down, keep left, past slip, you will see a green under the bridge, this is
the dive site. Drop off your gear then find somewhere to park.

Dive Site Description
An exciting dive for the marine life in an area awash with dangerous currents. Luckily for us and many others in the northwest of England and North Wales, providing the tides are right the Menai Straits under or around the Menai Suspension Bridge provides the diver with an all-year-round shore dive site, guaranteed! The down side is when the tides are not right it’s running at anything between 6 and 9 knots, but it’s best to dive it at a slack period to appreciate the sheer vastness and bio-diversity of marine life. Screaming drifts can be had but really only with boat cover.

Don’t take my word for it ask Bangor University of Ocean Sciences who regularly make studies of the area, especially under the Menai Suspension Bridge built by Thomas Telford in 1826. The Menai Straits in glacial times used to be estuarial, until afterwards when it became tidal bringing masses of nutrients along its length. The turbo-fed marine life thrives in this area and visibility is reduced as a result, but who cares its awesome to dive for the marine life!

Under the bridge is a small island called Pig Island and this forms an underwater nature trail usually dived from west to east as the tide flows afterwards. The first thing the diver encounters are sponge cliffs, stepped walls of rocks covered in “solidified yellow custard” is the best analogy. Look closer and one will find a plethora of filter feeding marine, both sessile and mobile. Lobsters are one thing but hundreds of crabs of differing varieties can be found. Throw in a load of dragonets, scorpionfish, yellow coloured scorpion spider crabs, gunnel, many pollack and shells and you have the makings of a great dive.

The depth starts at zero to a maximum of 15m and usually the bottom composition of terminal moraine it is covered in dense carpets of very colourful and voracious dahlia anemones. In places huge beds of mussels dangle precariously off rock edges whilst at certain times of year masses of nudibranchs, particularly Dendronotus frondosus can be seen grazing.
The visibility can vary the average being 4m and sometimes it goes up to 8m. With this amount of marine life, it’s hardly surprising many of us divers crave this site all year round especially those with cameras with macro lenses fitted!

Dive Plan
Date of dive: Sunday 10th March Dive Site: Menai Bridge
Minimum Diver qualification; BSAC Sports Diver or above
Location: Anglesey North Wales Position: 53’ 13.275 N 004’ 09.885 W
Low Tide Menai: 12.55pm Low Tide Liverpool: 12.56pm Slack or predicted Dive time: 9.41am
Dive Boat: John Hughes’s Rib
Launching from: Menai Bridge Slip Position of slip: 53’ 13.430 N 004’09.675 W
Launch depth at launch site: All tide hights
Cox: TBA Assistant Cox: TBA
Dive Manager: Chris Heywood Boat Handlers: TBA
Maximum onboard: 2

Objective: To dive under the Menai bridge from Pig Rock (forth bridge pillar) following the current until the telephone cable is reached. At this point follow the cable going to the left. (NW ish)

Plan: Divers will arrive at 8.00am and attend a briefing given by the dive manager or his/her designated assistant. The briefing will consist of a reminder of the safety matters (including the risk assessment) and finalising buddy pairs.
Buddy Pairs: Buddy pairs will report to the Dive Manager that they have completed a SEEDS briefing with each other and that they are about to enter the water, they will then report back to the Dive Manager when they are out of the water.

Directions: Divers will walk 50 meters westwards up the hill, go through a gap in the wall and climb down the loose bank aided by a rope handrail. Make your way to the far right of the fourth pillar. If the timing is correct the current should be running from left to right (i.e., towards Caernarfon) and the tide will be falling.
Each pair of divers will use an SMB as well as each diver carrying a DSMB (and spare reel for diver with the SMB.) All divers will carry a knife or cutting tool (for fishing line). Parking: There is no parking at this dive site. Kit will have to be dropped off then cars parked in the village (5 minutes walk).

Plan details: The currents under the bridge can reach up to seven knots, so diving on neaps and on slacks is a must. To get maximum dive time, it’s critical be at the water’s edge 5mins before slack water occurs, to allow for a surface swim/walk or stumble across the channel to the island. When you are sure it is slack water, drop down to 10m keeping the reef on your left shoulder. Continuing along, the current will pick up slightly as you go under the bridge. When you see the telephone cable (which runs across the straights from bank to bank) follow it to the left. You should surface at the side of the stone pier (where you kitted up), follow this wall on your left shoulder) up the bank to the steps to get you back on top of the green.

Slack water: Slack water should occur 3 hours 15 minutes before low water Liverpool and lasts 1 hour
Safety Boat: The boat will be used only as a rescue boat.

i.e., to recover divers who have problems or have overshot the cable.

Risk assessment shared on branch email.