This article appeared in the May 23, 2001 edition of the Paducah Sun.

Depths in detail

Digital mapping provides most intricate look yet of big lakes

Maps on disk can show reservoir bottom contour changes as closely as every six inches of variation up or down.

By Steve Vantreese The Paducah Sun

Electronic technologies have been combined to provide the most detailed looks at what's beneath the waters of Kentucky Lake and Lake Barkley since they were impounded.

Pat Hahs of Murray, a public lands wildlife biologist for the Kentucky Department of Fish and Wildlife Resources, nowadays sidelines as a digital mapmaker of the popular, canal-linked fishing waters.

Operating as Kentucky HydroGrafx, Hahs has been mapping the bottom contours of popular fishing areas with a combination of sonar depth-finder, global positioning satellite instrumentation and computer. His end products are CD-rom disks that can be used on home computers to show - and make hard copy printouts, if you like - the most intricate views of lake floor contours ever recorded.

The options for electronically viewing or printing out depth information come as high resolution topographical maps , with depth variations color-coded, if you like - or as striking three-dimensional color maps that give a lifelike view of bottom contours, as if the viewer were seeing the floor of a drained lake from an aerial perspective.

"When I'm mapping, I run my boat at 5 miles per hour and take a data point every second with a depth-finder synchronized with a GPS," Hahs said.

"Recording the data points is the most time-consuming part of it. A lake section of 200 acres takes about six hours to record," he said. "That's why I'll only do select areas. It's just not feasible to map the entire lakes."

Areas already locked into HydroGrafx data are Kentucky Lake's Jonathan Creek and Blood River, two major tributary area standbys for crappie fishermen. Lake Barkley's Little River area has been the most recently mapped, and Barkley's Eddy Creek will be next. By summer, Kentucky Lake's western side secondary channels from the Eggner Ferry Bridge to Kentucky Dam, a network of structural features used by offshore bass anglers, will be probed and recorded.

Hahs electronically fingerprints each target area by running a tight grid pattern, covering the water like the morning fog so that the entire area being recorded is blanketed with data points. The GPS connection locates each data point to a specific place on the water, so a computer records an ultra-detailed look at the rise and fall of bottom elevations below.

Data collection also settles what Hahs does with his free evenings. The on-lake mapping is done at night. It helps him view his lit computer screen better, but there are fewer distractions in the form of other boats and wind-ruffled waves.

The greatest disclosures from Hahs' mapping are via the fact that his maps show bottom contours from only as much as two-foot to as little as six-inch intervals. Existing topographical maps tend to show bottom changes in intervals of four to seven feet. Old maps as a result show no changes at all in areas where contours are fairly subtle, whereas clear changes and bottom features are revealed by the finer incremental recordings of HydroGrafx mapping.

"The best existing topographical maps had been the old Corps of Engineers maps done of the areas before the lakes were impounded," Hahs said. "The newer maps actually have a decreased amount of details. With both of them, you'll look at some areas and they just appear to be blank because the contours the maps use are so large and the actual elevation changes along the bottom may be less than that."

The findings of more detailed data gathering have been eye-opening to Hahs as a fisherman.

"It's been a revelation about what the bottom is really like," he said. "With the more detailed data points, I've been able to see structures that I've never known were there. Some of them are features that a few regular fishermen have found on their own but have kept to themselves. They are their secret spots."

Mapping large embayment areas in fine detail has revealed many more typical fish-holding structures than appear on existing maps, providing more appropriate open water locations to sample fishing in a smaller area, he said.

"You can find more stuff on the map than you ever knew was there, and the good thing about it is you can use GPS to go right to the spot and find it from data that was on the map. Since they last year turned off the 'artificial error' that had been built into civilian GPS by the military, you can go straight to a bottom feature by using a GPS unit and the data points and get to within 10 meters of it. From there, you can find it on your depth-finder.

"I went crappie fishing one day after doing some data collecting, and I fished new spots that I had found just through my mapping," Hahs said. "I caught fish all day long. It shows you spots that are worth trying that you wouldn't see any other way."

Another observation, some creek channels that are boldly marked on maps actually are rather subtle nowadays. Hahs finds that some major tributary channels are silted in to the extent that they may exist as linear depressions of a mere one foot. While that makes them harder to find with only sonar units, they are still important to fishermen because fish continue to use even the nearly-leveled stream courses as migration routes between shallow and deep locations, he said.

Hahs' map disks are usable on most any home computer, and they offer even more function for those with both computer and GPS units. "The most basic, hand-held GPS units really work best with it," he said.

Ideal hardware for top benefits from the disk data are a combination of portable, hand-size computer and GPS that can be linked and used together right on the water, he said. "There are all kinds of possibilities for using the data with the technology that we have now," Hahs said. "Ten years ago you just couldn't have done this."

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