Can Someone Cross Check Figures

Looking at Choke Canyon:
- Want to know what Contour line to look at that will now be the shoreline as the lake is low.
- Something is not right when looking at the water level tables.
- Says the lake is at 30%.
- Another chart says it is 24.5 ft. below pool.
- That can't be right.

Thanks for your help.
Donald

It’s right, very shallow water lake and if it drops 4’ it will be nothing but a river channel.


If you look at a navionics card then it might be screwed up, they seem to have surveyed the lake when it was 20’ low and there’s a lot of the map missing.

There is a phone app out there called Lake Level. It shows Choke to be down 24.37 feet.

Here is a 5 ft interval contour map:
http://www.twdb.texas.gov/hydro_survey/chokecanyon/2012-06/ChokeCanyon_ContourMap.pdf

Look at the 195 ft contour and you should have the "Current" lake.

When looking at surface area v capacity, they are very different and the changes as a lake falls or rises will be very different from one lake to another depending on each lakes contours and depth.

All I need to know; looking at Nav. Apps. is:
- At what contour is the shoreline right now.

It would be easier to get on your graph and take off 25’ from the max/min water highlights.

At the current lake level the shoreline would be around 196’

I understand your dilemma Donald. I found that when Falcon showed to be down (I don't remember exactly how many foot) if I set the offset on my Navionics app to match that supposed level, it was not correct for what the actual level of the lake was. I want to say that the difference in where it was supposed to be and where it was was either 7 foot or 17 foot. I spent weeks looking at my app in my spare time, planning my trip accordingly. When I got there, all of my planning went out the window because the lake was so much higher than I had anticipated.

Donald, based on the data, it is correct. You just divide "current" stats on acre-feet of water by surface area, then compare this to full lake stats. I did it and it checks out.

Hmm? I know you are a stickler for mapping accuracy to optimize angling opportunities and I thought I'd share some math that relates to your low Choke Canyon Lake. Some stuff below. It shows that as a foot of additional water level is added to Choke Canyon, it raises the average depth of the lake by a fraction of the full foot, usually falling in the 30 to 50% range. The reason, and this relates to your contour lines, is as a lake adds each foot of water, it increases its area. Again, the attached chart shows that, generally, for each foot of water column added, about 500 acres of additional lake coverage occur. This additional acreage will be concentric . . . increasing its, what, "belt size" around its shoreline. This is what causes the average depth of a lake to drag behind a full foot of column water increase (or decrease). Our lakes have slope. To be 1:1, it'd take vertical walls as shorelines, then your contour lines' depths would change 1:1 with increasing or decreasing water levels.

Anyway, sum up the acres in the far column from 220' to 196' and that is how much acreage has shrunk . . . taking some of your contour lines along for the ride.

Brad


Ft Surface Acres Acre-ft Avg. Depth Gain % Added acreage
195 12,076.00 189,763.22 15.71407917
196 12,567.00 202,085.89 16.08067876 36.66% 491.00
197 13,035.00 214,889.92 16.48560951 40.49% 468.00
198 13,512.00 228,163.52 16.88599171 40.04% 477.00
199 14,005.00 241,915.50 17.27350946 38.75% 493.00
200 14,676.00 256,258.58 17.46106432 18.76% 671.00
201 15,232.00 271,221.97 17.80606421 34.50% 556.00
202 15,737.00 286,712.91 18.21903222 41.30% 505.00
203 16,144.00 302,657.15 18.74734576 52.83% 407.00
204 16,539.00 318,997.48 19.28759175 54.02% 395.00
205 16,954.00 335,741.41 19.80307951 51.55% 415.00
206 17,409.00 352,919.50 20.27224424 46.92% 455.00
207 17,919.00 370,577.35 20.68069368 40.84% 510.00
208 18,453.00 388,763.39 21.0677608 38.71% 534.00
209 18,988.00 407,484.21 21.46009111 39.23% 535.00
210 19,523.00 426,739.82 21.85831173 39.82% 535.00
211 20,058.00 446,530.22 22.26195134 40.36% 535.00
212 20,593.00 466,855.41 22.67058758 40.86% 535.00
213 21,242.00 487,750.03 22.96158695 29.10% 649.00
214 21,722.00 509,245.31 23.44375794 48.22% 480.00
215 22,244.00 531,219.37 23.88146781 43.77% 522.00
216 22,853.00 553,757.42 24.23127904 34.98% 609.00
217 23,558.00 576,956.01 24.49087401 25.96% 705.00
218 24,145.00 600,818.10 24.88374819 39.29% 587.00
219 24,689.00 625,233.93 25.32439264 44.06% 544.00
220 25,173.00 650,178.52 25.82840822 50.40% 484.00

There are way to many numbers in this thread

All typed in entered manually and calculated data using paper and pencil.

And all Donald wanted to know was, “what are the right contour lines on the navionics page”. I know they aren’t right, but I don’t know how wrong they are exactly. I know they are missing a lot of things that I have found by accident over the years and they make up bridges & culverts where none exist.

I thought that I accidentally logged into the math forum.

I am feeling like complete dumb-azz right now.

Ha!

The main take-away, without the numbers, is that a lake's percentage of full, say 30% full like Choke Canyon, is based on volume of water . . . 3 dimensional. A lake's drop in water level, its depth, is not.

Slope.

Assuming map contour lines are correct, some say they might not be, Donald would simply subtract the "down" amount from the lake level at the time the contours were calculated to determine new ones. A contour line of 30' will now be 5.5'.

Donald knows all of this . . . I think he was just asking about "down 24.5 feet" being consistent with the lake at 30% of full pool. It is.

Brad

If you pull up the navionics app (or have a navionics card) you will see that there is a lot of blue water that’s not mapped. It seems that they surveyed the lake when it was already down, not a shock since the lake is rarely full. I only remember it being full twice since it was impounded. So truth is, the contour lines haven’t been right in a long time. I have 2 nav cards, the older card is much more accurate than my newer card, but neither is really accurate even when the lake was full.

wish i hadnt started reading this my brain hurts. And i feel a little dumber

Where were you when I was in High School needing math help?

I'm not gonna comment.

https://youtu.be/O2djHEIxPVs