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Broadwater Lake - Intrepid divers brave astonishing depths and Weil's Disease Print

Godalming

Saturday, 15th Feb

Divers: Simon Gosling, Paul Harris, Ralph Hursthouse

Introduction

In a project at Broadwater Lake in Godalming, a large amount of silt had been dredged from the lake to form an island in the middle. A barrier had been constructed around the lake in order to keep the silt in one place.

Although the angling club has a dedicated team dealing with fisheries management, with an impressive array of equipment, several boats and a number of dry suits, they felt that an underwater inspection of this type was a bit beyond them and Dr. Alan Millington contacted Guildford BS-AC to see if we could help with the task.

Construction of the Barrier

The barrier has two layers, (Fig. 1) the outer is to provide strength and does not go all the way to the bed of the lake. The inner one comes back toward the island and lays on the bed of the lake. The weight of the silt should hold it down, then as silt gets onto the membrane, it is stopped and held back, but water is allowed to pass through.

Fig 1
Fig 1

Alan felt that the problem was likely to be with the seal at the bottom of the barrier, but as much as possible we were feeling for tears in the semi-permeable membrane too.

Along the outside of the barrier were bags of straw.  This is put into the water; as it rots, it releases an enzyme which makes Hydrogen Peroxide. This inhibits algal growth in the lake. Some 90 bales are used per year and a team of the fishermen’s wives (they sound as supportive as our diving wives) pull these bales to bits and stuff the hay into net bags.

The Dive

The day was very cold, with a thin layer of ice on the lake; Alan had already rowed over to drop off some people who were cutting back willow. He’d also taken the boat around the area we were to inspect to break the ice for us, since he’d gone to all of this trouble, Simon’s claims to have no air and forgotten various bits of kit in an effort to avoid the dive fell on deaf ears and he was soon whipped into a positive frenzy of enthusiasm to get into the water.

We examined the island from the shore and decided on a plan. This was to go and have a hot coffee and severely deplete angling club’s supply of Twix’s and Mars Bars. Having achieved our first objective, Simon and Ralph set about scaring local people in the car park who could not understand why anything that cold, blue and pimply should be walking and actually joking. These high jinks consisted of Simon hiding bits of kit under the piles of wood in his car (don’t ask) and the Ralph finding them for him. Cinderella, you shall go to the ball, whether you like it or not!

Visibility was expected to be poor, so we would enter the water a few meters apart and then work along the barrier by touch, overlapping slightly with the person in front.

We then moved onto the next section of barrier.

Rolling off of the boat into the 2 degree Centigrade, chest-deep water confirmed our emergency plan. If Simon did indeed encounter a low on air situation, he was not to signal his predicament to a buddy who would not be able to see him, but was to immediately stand up and breathe the air available to him on the surface.

Torches were an optimistic option, since at arm’s length, they could not be seen, even turning them on and looking directly into the beam made no difference.  Although we had planned to swim along the barrier for a 1st pass and then grub around at the bottom to inspect the seal on a 2nd pass, this plan proved to be impractical as moving the silt-covered straw bags quickly reduced visibility to zero.

Reaching between the two skins, no-one found any tears. Feeling along the bottom, for the most part you could only get your hand under by few inches.

The first fault was found when Simon was able to get most of his arm under the barrier (fig. 2), further round, in slightly deeper water (almost 2m, well nearly) we found an area where the membrane was not making contact with the bed of the lake (fig. 3) and so were able to confirm Alan’s suspicions that there was a problem with the membrane.

Fig 3 Fig 2
Fig. 2Fig. 3

We then de-kitted and were rowed back to the clubhouse, Simon beating his personal record of two boat trips in succession without feeling sea-sick.

After changing in the car park, much faster this time as Simon was not losing kit, we went back to the clubhouse to complete the job, i.e. ensure that we’d left no chocolate for the fishermen.

Conclusions

It was a challenging dive, not because of the depth, but the cold and the visibility. There were no free-flows and no entanglement issues.

Ralph has now done his first zero-vis. dive and first dive from an ice breaker. Simon can finally complete his dive planning and marshalling qualification as he’s now organized a dive without the involvement of our good friends in the RNLI.

A successful dive because the objectives that we had were met.

 
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