Figuring Out Underwater Topography

[DonovanHoggan]

Hi all,

I read a lot about finding drop offs, or shallow areas, or deep areas, or whatever but I have no clue how to find those. I can read maps well above the water line but do they exist for underwater?

I'd like to be able to afford a fancy sonar rig to put on my canoe but there's no way I'll get wife-approval on that.

Any other ideas?

Thanks
Donovan

[Jamie Black R/T]

You don't need to spend a ton on a sonar to learn about bottom composition.

A garmin striker or a humminbird helix 5 with a portable bag will double as a ice fishing rig and tell you all you need to know.

The big touchscreens with side imaging and live are awesome no doubt. But a entry level portable model will help you out a ton.

[stein]

Navionics is pretty accurate and free, no rivers are available so it depends what body of water you are on, most of the large and popular lakes are on there



https://webapp.navionics.com/

Shows classic drops like this where the contour lines are tight together

[A207X2]

Stein nailed it. If you're familiar with land-based topography, it's the same concept in reverse. Narrowly spaced lines mean a steep change in depth. His graph shows a steep drop off between 16 - 39. Widely spaced lines means a gradual drop off.

[SamSteele]

Underwater topographical maps are called bathymetric maps. You can find free versions for some lakes online. Some of these are based on old government soundings from the 70’s that’s aren’t very accurate. Others are highly detailed using modern sounder and gps technology.

Humminbird has “Liveshare” where people can upload their Autochart maps for other users to see and use. That’s a free resource for you, although it is somewhat limited for local lakes. Lowrance has their C-Map as well. I’m not as familiar with it, but I believe that it is similar.

SS


Sent from my iPhone using Tapatalk

[mapleleafman3]

I use a mix of them all, navionics, Liveshare and Cmaps. That covers most AB lakes. Also sometime i use the AB Gov bathymetric maps, but less often since the 3 apps/site have become more used and updated regularly. Another thing i use is Google Earth. It has a history function so you can see back in time. You can see what it was like at the lowest water level or maybe even before the res/lake was created.

AB Gov bathymetric maps (most are old, around 2008/9)
https://open.alberta.ca/dataset?tags=bathymetric+maps

[goldscud]

A distance marked rope and a weight does wonders if you don't want to spend any money on electronics

[Walleyedude]

Lowrance, through CMaps, has some very good mapping that you can access for free. Go to www.genesismaps.com and click on the "Social Maps" tab. You'll have to search around for Canada, and then Alberta, and then by the name of the lake.

You need a Lowrance sonar to download the map and use it live in your sonar unit, but you'll be able to find your favourite lakes and view them online. You can can pan around and zoom in to the areas you want and then take a screen capture and print it. The shoreline shows up as an air photo, which should help you get oriented between the bathymetry contours and where you are on the lake.

It's definitely worth a look!