A question for fresh water reservoir divers....

[Kim]

I have never dived in fresh water, but have discovered a reservoir near me that I might (I have to ask permission) be able to dive in.

At this time I'm not sure of the depths and what might be down there - I presume at least the old river beds, and maybe some buildings and sunken forest stuff. The dam has been there for about 30 years I believe.

My question concerns visibility at such a sight. Looking at the surface it seems quite murky - presumably due to the sunlight and algae growth etc. Is it reasonable to expect in such water that with some depth the algae growth drops off and the vis improves a bit? Or is it just going to be like that all the way down until the silt at the bottom?

I'm going to the office today to ask about it and see if there are old maps of the area before it was flooded. It appears that at least three river beds converged at this point where they built the dam. If I'm allowed to dive the site my plan would be to start at where one of the rivers enters the lake and follow the old river bed down mapping as we go. I'm assuming a max depth of 30 to 40 meters - the dam must be about 40 meters high, I'll check that today.

Any ideas/advice from people who dive these type of sites would be more than welcome. If I can make this work it would be fantastic. It would give me a dive site within 15 minutes of my house!

Of course....this is Japan....they might just say NO!

 

[The Kraken]

Needless to say, each impoundment will vary in its marine life etc., but generally as you get deeper, colder and darker the visibility will increase, at least it does here in the southeastern US, generally speaking.

Be careful, if trees were left standing there can be innumerable entangle hazards.

the K

 

[Logiconor]

While i dont know, nor claim to know anything about this, i should imagine the inlet for the dam creates some vicious currents

 

[scubadobadoo]

Here is a link to a reservoir I have been in. I have also inlcuded a link to my short review of this site. Perhaps you may find some similarities. Here, the visibilty get worse as you get deeper due to lack of light and a VERY silty bottom. Down to 60 or so feet, you often can get 30+ feet when the algea isn't blooming. The water here appears to possibly be more stagnant than your photos. As has been stated, every site will vary. My site has depths down past 160 or so ffw.

http://www.shorediving.com/Earth/USA_/New_Jersey_/Round_Valley_Reservoir/index.htm

http://www.state.nj.us/dep/parksandforests/parks/round.html

 

[Kim]

While i dont know, nor claim to know anything about this, i should imagine the inlet for the dam creates some vicious currents

If you look carefully at the first picture you'll see a row of orange bouys. I should imagine that that marks the exclusion zone for the inlets. I wouldn't intend to dive that close to the dam itself anyway. Look at the map and although it's a bit hard to see the dam itself is marked in red - there's a lot more dive able area not close to it. Those spurs are several kilometres long I believe.


Anyway - I'm going to go and check it out now a bit better. I'll let you know what I find out. I just asked my father-in-law who remembers it from before it was flooded. He says there wasn't that much but definitely a couple of roads and a few buildings.

 

[texdiveguy]

DUDE your not really a scuba diver till you hit fresh water,,,,,you might just like it!!!! Great looking site....have fun and report back.

 

[eponym]

From the scale of the spillway and the flooded-valley nature, it looks not too dissimilar from some of our Oregon resevoirs. I don't usually find viz over fifteen--five feet is more common in the summer. You may find a big thermocline after you pass the depth that sunlight can reach (often 15 to 20 feet), plus increased viz. I'm used to it being completely dark below fifty feet. Good for practicing compass navigation and other skills, trying out new gear, but not much to see. Those of ours that were put in thirty years ago were completely cleared out before filling.

 

[Kim]

Well. I just got back. I talked to the boss in the office there and he said "NO!!!" - it's completely forbidden. Of course he probably doesn't really have a clue and I need to run the chain higher to get to someone who understands the proposal. This guy just told me "too dangerous", although he did looked rather impressed when I flashed all my cert cards at him (about 7 or 8). Of course he didn't know what they meant but the Japanaese love licences!!!! Anyway, now I have a telephone number and a name to start with so I'll get my Japanese mate to start digging and see what we can come up with. That's always supposing that my mate is interested himself of course. If he doesn't like the idea i can forget it....oh well....

 

[Doc Harry]

Here in West Virginia I can get in a "night" dive during the day just by diving deeper than 80 feet in the reservoirs. It is totally dark down there. There is a very defined thermocline. And visibility sucks, 5 feet.

 

[DA Aquamaster]

The height of the water level over the outflow channel will give you a good indicatopr of maximum depth.

I'd definitiely find out where the head works are and I suspect the bouy markers are there to keep people away from the head works. I noticed once when I got too close ot the headworks of a hydroelectric damn that I was drifting along the bottom in what was normally a currently reservoir. Headworks an low visibility can be a very dangerous combination.

The topography does not change much underwater in a reservoir like the one pictured - it will mirror what is above the surface with steep sides ending in a relatively narrow river channel. The bottom is often logged in reservoirs to keep trees from poking above the water and to make use of an otherwise wasted resource. However finding trees that were left in limited viz at depth can be a bit dangerous as the canopy will be spread out above you crreating more or less an over ehad environment that may be chock full of monfillament and other entanglement hazards.

Deeper lakes tend to have better visibility. It's a combination of a lack of sunlight as well as a lack of oxygen. There are lots of bacteria living in the silt in the bottom decomposing whatever drifts down there and that biological activity depletes the O2 level. In a temperate climate, the lake will turn over twice a year as water expands and becomes less dense as it cools below 35 degrees F. That causes it to rise and freeze at the surface rather than on the bottom (which is very fortunate as without that physical charateristic, we'd all live on an ice planet.) In the spring as the water warms above 35 degrees it sinks back down through the water column. So visibility at depth often varies with the season and can also vary from year to year. Locally we have alpine lakes with very little viz and night dive conditions below about 60 ft, while others are very clear with 30 ft viz and adequate ambient light (for everything other than reading a guage) at 130 ft.

Visibility at the surface is also affected by algae blooms that become more pronounced at temps about 70-75 degrees. Agricultural runoff with excess fertilizer (natural or man made) can greatly magnify algae blooms.

Deeper lakes in general though stay cold at depth due to the heat capacity and general insulation properties of the water above. It's not uncommon to find 40 degre temps in a deep (greater than 100-150 ft.) freshwater lake in August with 2 or three thermoclines from the surface to the 100 ft level.

Visbility varies based on the soil the lake is in wave action, the type of inflow it receives and the flow through the lake. Reservoirs with fairly silt free inflow, rocky sides, well forested or vegetated banks, little wave action and deep depths can have very good visibility (for a lake) in the 30 ft range.