Lake Washington PBM and Boeing I-90 bridge section

[lamont]

A few weekends back we went out with Bill Minton and northwestdivecharters.com on Lake Washington and dove the PBM and the I-90 bridge section in the very south end of the lake. These are a couple of really good dives for recreational divers which I have not seen anyone exploiting in recent years.

The PBM is about 70 feet deep and is a small wreck. There's good info on the interwebs about the plane and its history as a divesite (boydski's site, etc). We did the first dive on that wreck and got some nice vid of it. The plane is turtled and the back has been ripped off in a salvage attempt. One of the divers on this dive (Larry) had actually dove it in a previous diving life when the plane was whole. It looked pretty much like I'd remember it from before.

The I-90 bridge section makes for a good second dive since its basically a slab of concrete about 500 feet long which means that you can actually spend some time swimming around it. I don't think anyone knows the story of exactly how the bridge section wound up where it did, but it runs from around 20 foot depth at the shallow end to 60 feet at the deep end, there's some overhang on the shallow end. On the deeper end there's a little maintenance shack of some kind. It looks like it fell down on a large I-beam girder structure which has also broken the concrete up in the middle. You can follow the I-beams out a bit and you can see quite a bit of that in the video.

One of the hazards of these dives is low visibility and we slammed into some really suddenly on the bridge dive. As me and Serge were heading out deeper on the bridge the viz started to close down, I put my hand on the concrete railing of the bridge and just a few kicks further and while I could see serge a foot away from my face, I couldn't see my hands any more and my left hand was on the railing and my right hand couldn't feel any bridge. I have no idea if we were about to go off the end of it or if the railing just temporarily ended, but with only inches of viz we had to turn back, so I didn't get to video the shack.

The overhand at the shallow end is also probably a hazard. I don't remember how far it goes in and viz was bad enough that I couldn't see into it and didn't want to run a line in there on this dive. Recreational divers should stay out of there. All we did was duck under the overhang and turn around and film bubbles, which is good enough for a thrill.

The bridge section also comes very close to the south shore of Lake Washington and there were a bunch of jetskis that were zipping around there at one point before the dive. Its most likely better to plan the dive to be surfacing closer to the middle of the bridge (which is where bill dropped us and picked us up later). As usual with lake dives you simply need to be conscious of all the surface traffic and plan appropriately.

These dives make really good training stepping-stone dives. There's been nobody running charters out to them ever since Porthole went under, so hopefully people will see this and get out there and start diving them with Bill. He did an excellent job and dropped us smack on the PBM and he's got the coordinates for both of these sites now.

Both the sites are completely within the reach of recreational divers. They are advanced dives due to the viz, surface traffic, the square ascent profiles, the general darkness of the lake, hazards associated with wrecks and structure at depth, etc. But we had a mix of divers and experience on the boat, with two single tank divers, including Jan who is a lady with bilateral total joint replacements in both knees, so it doesn't take a badass tech diver in doubles to dive these.

Bills boat for lake diving easily fit 4 divers with 2 doubles divers and 2 divers with 2 single tanks. Scooters and deco bottles would make it a lot more cramped, and you don't reallly need them here. Although Bill is also available for tech dives on other targets in the Lake, and one point of this dive was to get Serge out and meet Bill and boat and go for a dive so that he'd have him as a resource for his current Tech1.

And now I'll stop yapping and you can watch the vids:



http://vimeo.com/49663727



http://vimeo.com/50460899

[CaptnJack]

Portions of the bridge sank in November 1990 during maintenance activities
http://www.wsdot.wa.gov/partners/irt/Ma ... Report.pdf

[ljjames]

Thanks for that link Richard, but is that referring to the pieces that are in the south end of the lake that Lamont is talking about? or the large chunk that folks dive from shore under the current I-90 bridge?

[CaptnJack]

That pontoon was, I think, used by the old shuffleton power plant. The outfall is just east of it, looks like a irrigation flume.

[ljjames]

Ah cool! very interesting! Thanks!

That pontoon was, I think, used by the old shuffleton power plant. The outfall is just east of it, looks like a irrigation flume.

[CaptnJack]

WA has built alot of pontoons and pontoon-like things over the years. The multibeam bathymetry around both bridges is littered with pontoon stuff. I'm not 100% sure that's actually a bridge section, I've only been there once personally quite awhile ago when I couldn't find the PBM. The powerplant is long gone, it was east of the Boeing hanger and west of the creek, there are condos in that general area now. I'm pretty sure it was part of a larger Boeing operation there. You'd think the sediments off the flume would be nasty, but they are surprisingly average. Who knows, maybe the pontoon was for flying boats, so its somehow affilated with the PBM in provenance.

[Nwbrewer]

WA has built alot of pontoons and pontoon-like things over the years. The multibeam bathymetry around both bridges is littered with pontoon stuff. I'm not 100% sure that's actually a bridge section, I've only been there once personally quite awhile ago when I couldn't find the PBM. The powerplant is long gone, it was east of the Boeing hanger and west of the creek, there are condos in that general area now. I'm pretty sure it was part of a larger Boeing operation there. You'd think the sediments off the flume would be nasty, but they are surprisingly average. Who knows, maybe the pontoon was for flying boats, so its somehow affilated with the PBM in provenance.

I can't remember who told me this, but I thought the pontoon that was floating at the south end of the lake off the factory was part of the original I-90 bridge. It was part of the center span that was designed to be moved out of the way for boat traffic. (Like 520 does now). As I say, I can't recall the source, so the information is suspect.

[CaptnJack]

I love rumors like this!

[lamont]

WA has built alot of pontoons and pontoon-like things over the years. The multibeam bathymetry around both bridges is littered with pontoon stuff. I'm not 100% sure that's actually a bridge section, I've only been there once personally quite awhile ago when I couldn't find the PBM. The powerplant is long gone, it was east of the Boeing hanger and west of the creek, there are condos in that general area now. I'm pretty sure it was part of a larger Boeing operation there. You'd think the sediments off the flume would be nasty, but they are surprisingly average. Who knows, maybe the pontoon was for flying boats, so its somehow affilated with the PBM in provenance.

The street lamps, the railings and the little hut on it match pics of the old bridge. I cant find a really good identifying image this AM of the exact pontoon span but we tracked it down at one point.

It might be the section that moves, the hut might have been a control room for that?

Good excuse to go back and get some more identifying vid of it I guess...

[Nwbrewer]

Good excuse to go back and get some more identifying vid of it I guess...

Some super crappy video of Lurch and I diving it a few years ago.

http://s180.photobucket.com/albums/x264 ... =Movie.mp4