The Dredging of Grand Haven Harbor
The posted coordinates will bring you to an impressive view of the Grand Haven Harbor, which connects the Grand River Watershed to Lake Michigan. This channel is actively managed by the Army Corps of Engineers. The depth of the channel at this area is between 18-21 ft, diving down to 23 ft at the western terminus of the channel. However, this depth is far from constant! The channel regularly fills with large deposits of sand. Each year, the Army Corps of Engineers dredges approximately 35,000 cubic yards of sand from the channel!
Where Does All That Sand Come From?
The Grand Haven Harbors receives water from the Grand River, which runs for 260 miles across the lower peninsula of Michigan before reaching this harbor. The lower peninsula of Michigan is covered in sandy soils and sediment that cover the underlying bedrock. These sands are from glacial till, which are small particles deposited during the retreat of glaciers in this area. The river can wash away these sediments, which travel along with the river's current.
Like many of the Great Lakes, Lake Michigan is known for its turbulent waters. During storms, large waves develop that can churn up underlying sand and deposit it on the shoreline. The eastern shoreline of Lake Michigan is well known for its sandy beaches, many of which are subjects of other Earthcaches!
Logging Requirements
To log your find, observe what you see at the posted coordinates and then send me your answers to the below questions. Please log your find after submitting the answers.
1. You are standing on the south bank of the harbor. Compare this bank to what you see on the north bank. Do you think both shores contribute equally to sand in the immediate area? Why or why not?
2. Look west towards the mouth of the river as it enters Lake Michigan. Do you see anything that either helps or prevents sand from the bottom of Lake Michigan entering the harbor during rough storms?
3. Look at the water in the main channel. Is the current flowing out towards lake Michigan, or inland toward the Grand River? Based on this, where do you think most of the sand in the channel is coming from?
4. At the posted coordinates, you will find an Army Corp of Engineers survey disk (look for the metal circle inlaid on the dock). To log this find, please post a picture of your feet, or other personal item, next to the benchmark.
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