Figure 7. Silver Lake 2012 depth contour map (Progressive AE).
Figure 8. Silver Lake dune migration 1938 to 2010.
Figure 5. Silver Lake 1950 depth contour map (Michigan Conservation Department).
Figure 4. Silver Lake 1892 depth transects (Michigan Fish Commission).
Lake Mapping: An Overview of Methods and Potential Uses
A primary use of any map is navigation, but a map can also show prime fishing locations, bottom substrate, plant growth areas, spawning sites, depth and shoreline changes, and a variety of other features. This article provides an overview of historical and current lake mapping methods and how this information may be useful in understanding and managing your lake.
Historical Mapping Techniques
Figure 1. Weighted depth sounding line. (Left: weight; right: line on reel.)
The spacing of soundings has an important bearing on both mapping accuracy and speed. Insufficiency of depth records may result in an inaccurate map, or one that does not give adequate information for management. On the other hand, over-intensive sounding wastes time and effort. It is difficult to prescribe a definite pattern for spacing depth measurements because of the variability of lake basins. Good decisions on how frequently soundings should be made increases with experience. The following is a general guide relating lake acreage to sounding interval when mapping is done on ice: 5-acre lakes - 50-foot intervals; 10-25 acres - 100 foot; 50-300 acres- 200 foot; larger lakes - 300- to 400-foot intervals. Additional soundings are often necessary between shore and the drop-off, in and around shoal areas that occur well out from shore in some fairly deep lakes, and throughout the basins of lakes in which depths are highly variable. Incompleteness of depth data may become evident as a set pattern of sounding is in progress; in such cases additional measurements should be made in the questionable area...
Soft bottom can cause significant errors in depth measurements. The bottom may be so soft that the sounding weight passes through it almost as freely as water. In such areas sounding must be done with extreme care, and the cup which collects bottom materials should be inspected often to determine the top level of the deposits. After some experience, one acquires a “feel” for the difference in descent of the weight through water and through very soft bottom, which helps greatly in locating the boundary between the two strata...
Bench marks are established for measuring lake level fluctuations. They can be very useful. Trees, bridge or dam abutments, and concrete foundations are among the objects that may serve as bench mark monuments. Spikes serve as reference points in trees, and a cold chisel is used to etch concrete or steel objects. Measurements of water elevations are made with either a surveyor’s level and leveling rod, or a line level, chalk line, and leveling rod. Plainly record elevation, location, and establishment date for each bench mark on the field map. Bench marks should be established at the time the lake is mapped so that those data can be included on the finished map...
Re-Mapping Silver Lake, Oceana County
Figure 2. Aerial view of Silver Lake sand dunes.
Figure 3. Silver Lake sand dunes.
|Lake Surface Area (Acres)||690||672||-18 (3%)|
|Maximum Depth (Feet)||25||22||-3 (12%)|
|Mean Depth (Feet)||14.9||14.6||-0.3 (2%)|
|Lake Volume (Acre-feet)||10,287||9,823||-464 (5%)|
Figure 9. Silver Lake depth contours on registered aerial photography.