Underwater benchmarks

[Dionyzus]

I see a recent topic on underground benchmarks so I thought I'd bring up one with a slight difference.. underwater benchmarks! What I mean is not a deliberately placed one (like in the Lasting Impressions book), but a BM on land that has since been covered by water, such as a reservoir.

 

I've seen some examples of these marks in Texas lakes, such as BL1018. This marker is on top of a bridge abutment, which could probably be located with sonar. Then it's a simple matter of donning the scuba gear to get a close up shot! Of course most Texas lakes are notoriously muddy, but perhaps other parts of the country with clearer water may be better for finding this unique kind of benchmark.

[+2/3 Marine]

I know this isn't quite what you were getting at but.... I recovered KK0696 the day after Thanksgiving, this year, on the edge of the North Fork of the South Platte River. It was on a large flat boulder, at the edge of and in the river. The BM was about 6" above the level of the water line at this time. I don't know how many CFM the river was flowing at this time, but the river was low. During the Spring runoff i'm sure that the BM can't be seen for 2 to 3 months, maybe more. I thought at the time it was a strange place for it to be placed, as Colorado doesn't lack for any boulders to use in this area. I wasn't thinking or I would have taken an area view of it to post.

[+StarDoc]

In northeast Montana, there is an entire string of them along the original course of the Missouri River that are now under Ft. Peck Reservior. They were placed back in the 1930s, before the dam was built. I'm not really sure how far down they are now...

[Relic_Hunter_Finder]

Reply: Well, I'll give you guy's an E for effort. I love this sport; however, I'm not willing to put a lot of money into expense gear for underwater recordings of geographical survey benchmakers