Technological Advances in Lake Mapping
Advances in technology have helped make lake mapping much easier. In the not too distant past, lake mapping was done by hand. Holes were drilled through the ice and weighted drop lines were used to measure depths and collect bottom samples. This was a laborious process that often took many days to complete. Much of this mapping was conducted by the Michigan Conservation Department Institute of Fisheries in the 1940 to 1970 timeframe.
Computer software is now available that allows hydro-acoustic soundings collected with a depth finder to be used to create highly accurate depth contour maps. In addition to water depths, measurements of plant bio-volume (i.e., the height of plants in the water column) and bottom hardness are also possible. Navico BioBase is one of the companies that helps users convert their hydro-acoustic (SONAR) data into digital maps. Below are some examples of maps created with this technology and some interesting side notes.
There is a common perception that lakes quickly fill-in with sediment and become shallower. However, most lakes appear to be filling in at a very slow, almost imperceptible rate. Often, lake depths shown on historical maps from many years ago are nearly identical to present day lake depth measurements. An exception to this general observation might be an impoundment receiving a substantial sediment load or the portion of a lake at the mouth of a tributary where sediment accumulates.
However, when comparing present-day maps with historical maps, changes in shoreline configuration are often observed. These changes are often the result of channelization and other shoreline alternations that occurred primarily in the 1950s and 1960s as development pressure on lakes increased. Most dredging and filling activities around lakes ceased with the enactment of Michigan’s Inland Lakes and Streams Act and the Wetland Protection Act in the 1970s.
Natural fluctuations in water levels can also affect shoreline configuration. In lakes prone to considerable fluctuations in water level, shoreline configurations can change as lake levels rise and fall. In some lakes, fluctuations in water level can be so great that the lakes can be substantially larger during periods of high water than during periods of lower water levels. When mapping lakes, the lake level should be noted at the time of the survey.
Bio-volume is a measure of the height of plants in a lake. In shallow lakes, plants can grow over much of the bottom while, in deeper lakes, plants are generally restricted to portions of the lake less than about 15 feet. Changes in bio-volume can be expected both seasonally and year-to-year. Generally, plant growth is sparser in the spring and, as summer progresses, plants are found over a greater portion of the lake and growing higher in the water column. Year-to-year changes can be evident due to variability in weather, variations in water level, or other factors. Greater bio-volume would be expected after a mild winter or a warm summer, while less bio-volume would be expected after a harsh winter or cooler summer. Similarly, plant bio-volume during periods of prolonged high water levels would be expected to be less than during periods of low water levels. When evaluating plant bio-volume over time, climatological and lake level fluctuations should also be considered.
From a lake management perspective, another important use of bio-volume measurements is to evaluate the impact of exotic plant invasions. Infestations of exotic species such as Eurasian milfoil or starry stonewort can increase bio-volume as these plants tend to grow higher in the water column than many native plants. These plants may also colonize areas of the lake that were formerly free of plants. While bio-volume does not reveal which plants are in a given lake, bio-volume measurements can be supplemented with plant identification surveys to evaluate plant types.
Hydro-acoustic soundings can also provide a generalized view of hard versus soft sediment in a lake. Most often, near-shore areas or wind-swept portions of lakes have firmer sediments while deeper areas or isolated coves have softer bottom sediments. In some lakes, changes in bottom hardness appear to be related to seasonal influences with softer sediments measured in shallow areas after ice-off and firmer sediments measured later in the season. This difference may be due to wind and wave action during ice-free periods and scouring of soft sediments from near-shore areas as a result of summer boating activity.
Advances in lake mapping technology are having a significant impact on lake research and management projects. These advances are making data collection and monitoring efforts less time consuming and more cost-effective. If you do not have a map of your lake or want to update an existing map, there is now a relatively easy way to do it.