Silver Beach County Park:
Located at the mouth of the St. Joseph River, Silver Beach features a clean, wide beach on Lake Michigan with public access to the South Pier.
Long Shore Drift:
Creation of Silver Beach was due in the most part to wave action. Waves, washing onshore (Swash) move in the same direction as the prevailing winds. These waves collect sand from the bottom, wash in, and deposit some of the particles on the beach before retreating. The retreating (offshore) backwash, due to gravity, always flows perpendicular to the shoreline. As this backwash loses energy, it drops more of the sand particles during its retreat. The next wave again picks up the particles and moves them slightly further down the beach. This zigzagging of wave action causes a lateral movement of sand along the shoreline in one overall direction. This process is called Long Shore Drift (LSD) and can be observed on all beaches. Most sand is deposited into lakes near the mouths of rivers and is moved along the shoreline by the effects of LSD. Long Shore Drift is the main cause of long strips of Great Lakes coastline being covered in sand.
Deposit and Loss:
Despite the constant forces of LSD carrying sand away, Silver Beach continues to exist in a state of dynamic equilibrium. It’s an ecological system kept in balance by an assortment of forces further complicated when people are factored into the equation. The beach is an unpredictable place to build houses once Long Shore Drift steps in. Without sand replenishment, homes built far from the waters edge could eventually find themselves with waves lapping at their doors, victims of shifting sands.
Stabilization:
One solution to this problem is the construction of jetties, groins and sea walls. A jetty is a structure built perpendicular to the shore extending out into the water. Its basic use is to hold sand in place and prevent it from washing away. Typically, jetties are concrete structures built at inlets and channels to help maintain shipping and navigable waterways. Groins are built perpendicular to shorelines and are similar to jetties. Groins are generally built on straight stretches of beach, away from inlets or channels. They are often built as parallel structures in a series of 2 or more. Construction could be of concrete, steel, wood or stone. A sea wall, is a wall built parallel to the coastline at the edge of where the land meets the water. Sea walls are typically made of concrete or stone. While structures such as these protect beach homes and other buildings from erosion, they can cause increased erosion further down the shore. Both jetties and groins act like dams and physically stop the movement of sand. As a result, a buildup of sand occurs to the side protected by the structure. Areas further down coast are cut off from natural LSD and are no longer replenished by the sand that usually fed them, causing erosion.
Email your answers to the questions below, to me, using the link in my profile only. If your answers are not received by me, your log will be deleted. Photos are accepted and appreciated as long as the answers are not pictured. You do not have to wait for confirmation from me before logging this cache as completed. Most of all……learn……and enjoy the view.
1. In what direction (north or south) is the LSD on the day of your visit?
2. What do you believe is the direction of the prevailing (usual) winds, and thus the "overall" direction of LSD? Explain your reasoning for this answer.
3. With Long Shore Drift and no resupply, you have loss of sand. List 2 factors that help keep this beach covered in sand.
Permission for this EarthCache granted by
Brian Bailey, Director
Berrien County Parks Commission
T: 269-983-7111 Ext 8007
F: 269-982-8661