Submergent Aquatic Vegetation Mapping Lake Minnetonka Area, Hennepin County

Lake Minnetonka Area, Hennepin County

QuickBird imagery was acquired on July 28, 2002 of the Lake Minnetonka area. The lakes include Christmas Lake (655 ha) in Hennepin County, and West Auburn (645 ha) Lake in Scott County, Minnesota. The Minnesota Department of Natural Resources collected the field data for these three lakes.

For this study the field data specifically targeted submerged plants using an echo sounder equipped with a GPS unit. The hydroacoustic survey collected data pertaining to lake depth and plant depth at thousands of points in the shallower portions of the lakes where aquatic plants were present but not at the surface. General point survey data were collected in areas where the submerged plants were topped at the surface or where there were floating or emergent plants.

We followed similar imagery processing procedures for the lakes south of Lake Minnetonka as with Swan Lake emergent vegetation mapping with the exception of also stratifying the open water areas before classification of the submerged and emergent/floating aquatic plants. See examples of the resulting maps to the right.

Preliminary review of the aquatic plant assessments of West Auburn and Christmas lakes indicates that submerged plants can be separated from open water areas and classified to a plant top depth of around 2 m. It also appears that submerged plants with more dense growing characteristics like Eurasian watermilfoil (an exotic to Minnesota lakes) can be separated from other submerged plants that tend to have less dense growing characteristics.

Echo Sounders are measuring instruments that send out an acoustic pulse in water and measure distances in terms of the time for the echo of the pulse to return.

Hydroacoustic Survey Set Up

Hydroacoustic Survey Set Up

Christmas Lake Aquatic Plant Map

Christmas Lake Aquatic Plant Map

Christmas Lake Depth to Plants Map

Christmas Lake Depth to Plants Map

West Auburn Aquatic Plant Map

West Auburn Aquatic Plant Map