Lake Bathymetry & Sediment Deposition in Iowa Lakes

PROJECT PERIOD: Continuous since 2001
PROJECT CHIEF: Greg Nalley (email Greg Nalley)
STUDY AREA: Lakes and Reservoirs statewide
COOPERATING AGENCY: Iowa Department of Natural Resources


The Iowa Department of Natural Resources (DNR) is mandated by the Environmental Protection Agency to create a total maximum daily load (TMDL) limit for many constituents in Iowa waters. Sediment load and deposition is the concern in this study. The Iowa DNR is required to know the rate at which sediment is being deposited in reservoirs. Until recently, technology has been lacking in for shallow water seismic data collection. In 2001, the USGS Iowa Water Science Center acquired new equipment capable of viewing layers of material below the bottom of a lake, and calculating sediment volumes.


  1. Measure the thickness and volume of sediment deposited in a reservoir since it was constructed.
  2. Define the elevation of the lake bottom.
  3. Create GIS coverages with contours of the lake bottom elevation, and sediment thickness.


Layers of material below the lake bottom are measured by an array of five hydroacoustic transducers developed by Specialty Devices, Inc. (SDI) ranging from 4 to 200 kHz. Differential GPS is used to determine the latitude and longitude of each point measured by the transducer. A ruggedized laptop computer is used to collect and process much of the data on site.


Since 2001, 13 lakes have been surveyed for sediment thickness with the current equipment in Iowa. The data is currently in review, and is yet to be published. The equipment has been tested in environments outside of Iowa as well. Personnel from the Iowa USGS have used the equipment on a river in Minnesota to locate where silt is being deposited. A reservoir in Breckenridge, CO has also been surveyed to determine the volume of sediment that has been deposited.

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