Topic: Autochart - Dealing with Changing lake levels?

[john h]

From what I understand, you can adjust the water level when you import a set of data in Autochart to compensate for a lower level of water.

I am trying to understand how this feature would best be used for my circumstance. The local lakes that I fish have their water levels managed by the water board.  This means the levels fluctuate up and down a lot and what may have been underwater one month, may be dry land the next.

So as an example, I have a local lake that has a spillway water level of 361.67 m (around 1186 feet) (this is level measured above sea level) and I have these data files with the water level of the day indicated:

Feb 2014 - 347.46m
Feb 2013 -  344.52m
Feb 2012 - 356.12m
Feb 2011 - 359.56m
Feb 2010 - 345.13m

Now I want to go out tomorrow and the current water level is 352.1m.

How would I go about adjusting the map so it matches the current water level?

Would I have to re-import all the files and adjust to today's level? What if I have 100 sets of files from 100 trips? Is there a way to bulk update?

[CamoHunter]

Once you import the data, and tell it how far above/below the water level it was on the data you're importing, that's all you need to do. 

For example, here's how I would do it. 

Determine a depth control that you will use for every import for that lake.  For your case and the water levels you listed, I would use 359.0m as the control.  So when you import Feb 2010 data, it'll ask you for water level, and you'd say it was -13.87m (359.0 - 345.13 = 13.87).  When you import Feb 2011 data, you'd say it was +0.56m.  When you import Feb 2012 data, you'd say it was -2.88.  Etc. 

Then, at all times you're in Autochart it will adjust your data to the 359.0m water level and show water depths at that level.  It'll update your Zerolines SD card lakemaster map to depths at water level 359.0m.  If the water level is lower than that, lets say 352.1, you'd adjust that on your Humminbird depthfinder.  For example, you'd hit Menu, go to the Charts tab, and down to "Water level offset", and adjust it to -6.9m.  Your humminbird will adjust the lakemaster depths to the current water level depths. 

Hope that makes sense, let me know if it doesn't.

[john h]

That makes perfect sense. I wasn't aware of the depth offset function in the menu. Thanks for the reply.

[john h]

I just checked my unit and I don't have the "water level offset" menu item.  I assume this comes with the firmware update that enables Autochart.

[john h]

I was having a browse through a manual and the water level offset will only allow +-10 metres (30 feet).

So this method will not allow enough variation to match the changing levels of my lakes.

[CamoHunter]

If it only allows +/- 10 meters, probably use a little lower number for your 'control' water level.  Instead of 359.0, I'd probably use something closer to 350.0 for the 'normal' water level.  Then when you import levels higher than that in autochart, it'd be +9.56 for Feb 2010.  That should allow you a little more wiggle room with the 10meter limitation  for water level offset on your Humminbird depthfinder.

[Bob B]

Seems like if you choose a water level in the middle you would have a total of 20 meters - 60feet.........+10 to -10 meters

[john h]

I had a look at one of the other lakes I fish and it's full level is 1163.8m and the current level is 1139.4m so the difference is 24.4m (80 feet). So this method would not work on that lake at all. It starts to get real messy.

Perhaps Humminbird could extend the adjustment parameters?

[CamoHunter]

Forgive me, but does it have to be exact?  So what if on your depthfinder, it shows the contours 2ft higher than the lake level actually is at it's lowest level.  Can you do subtraction?  To me, as long as it is pretty close, and you get the idea of the layouts with the contour lines, the actual depth number doesn't matter as long as you can figure it out by subtracting a couple ft.

[john h]

In the last example I gave the difference would be 14.4 feet, so a bit more than 2 foot.

I could not worry about adjustments and do math out on the water, but it sort of defeats the purpose of the technology doesn't it?

Looks like Reefmaster might have a solution in the works anyway.

[CamoHunter]

Okay, just raising a question.  Didn't know it it would be a deal killer or not.  Guess it is in your case.  That lake must fluctuate a LOT!!  I thought mine fluctuated a bunch at 20ft above or below normal pool elevation!  I do not envy your lake level predicament one bit!  Good luck with searching for a solution.  Cheers!