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DNR To Continue Mapping Of Lakes

By Staff | Mar 27, 2008

SPIRIT LAKE – For more than 30 years, anglers had fisheries biologist Earl Rose to thank for leading them to the rock reefs, deep water flats and underwater humps found on the hand-drawn contour maps of Iowa lakes. But after 30 years, many of Iowa’s lakes have changed and much of the information on those 1970s maps is no longer accurate.

Developing new lake maps became a necessity to meet the requirements of Iowa’s lake restoration program. Lakes targeted for restoration or for special projects were top priority when the DNR began the huge task in 2006 of remapping Iowa lakes. The new information collected will be used to establish baseline information in a statewide lakes database that can be used to document changes over time.

Once the initial set of priority lakes are mapped, the focus will shift to mapping other key public lakes, and plans are in the works to map some of Iowa’s largest lakes.

Creating a lake map takes a plan. The plan for each lake is created by analyzing new aerial photography and the old survey data in a computer system.

The maps are created using data collected by a single beam sonar and Global Positioning System (GPS) clamped to the side of a boat and driven over the planned grid. The more variable the lake bottom, the greater the number of lines in the grid. Wave action can affect the quality of the soundings and the boat can travel no faster than seven miles per hour.

The sonar device is an 8-inch diameter brass transducer that is positioned nine to 10 inches under the water and has a survey-grade GPS antenna is placed above it. The sounder works kind of like a fish finder. It shoots a sound pulse at the bottom of the lake, which bounces off the lake bottom and back to the boat where that data is collected in an onboard laptop computer.

Mapping a small lake does not take much time. From set up to break down, a 250-acre lake can be mapped in two to three hours. Recording the data is only the first step, however. The data recorded from a 250-acre lake can have 10s of thousands of individual soundings. Each sounding must be checked to make sure it is correct and false soundings are eliminated. A 600-acre lake can have between 200,000 and 300,000 soundings.

The next step is to create a bottom surface, then add contour lines. Finally, a map must be created.

“That raw data needs to be turned in to something, that means something to someone,” said Mike Hawkins, fisheries biologist with the DNR at Spirit Lake. Colors are added to define different water depths, public amenities, like boat ramps, parking areas, are added to finish the map. “This next step takes a lot of work and some artistic touch to make the maps look nice,” he said. Finally, the map is sent out for review before it is put on the web.

So far, there are 10 new maps available in black and white and in color on the DNR’s website http://www.iowadnr.com/fish/index.html then click on Where to Fish, with more new maps are on the way. The maps are currently not available in downloadable formats for GPS systems.

These new maps have the ability to be updated and published should changes occur. The local fisheries biologists are using a new statewide database to update information in their districts. They can add locations of new fish structure or a new boat ramp into the database. This new information can easily be updated on the map and republished to the internet.

So far, the DNR has collected soundings on 44 lakes. New maps are currently online for Big Creek Lake, Beeds Lake, Black Hawk Lake, Lake Cornelia, Easter Lake, Five Island Lake, George Wyth Lake, Grays Lake, Lake Hawthorn and Hickory Grove Lake.

The next maps to be added to the website will be Lost Island Lake, Meadow Lake, Prairie Rose Lake, Lake Manawa, Little Wall Lake, Lake Wapello, Lower Pine Lake and Lake Geode.

Hawkins said they will be collecting data on about 30 lakes this year, including Red Haw Lake, Lake Ahquabi, Lake Belva Deer, Brushy Creek Lake, and Storm Lake and have maps available sometime during the winter 2009.

The Iowa Great Lakes have not been re-mapped. Hawkins said they are looking into an upgrade of the sonar equipment that would provide much greater lake bed detail and allow them to work more quickly. But, new multi-beam sonar is also much more expensive.

For more information, contact Hawkins at the DNR’s Spirit Lake Fish Hatchery at 712-336-1840.