This is an Earthcache – as such, there is no physical cache. Instead after examining the shoreline at the posted coordinates you will answer 6 questions and message me the answers. This earthcache is located in Leesylvania State Park with permission. For more information about hours of operation, parking fees, and park rules please visit this LEESYLVANIA STATE PARK link.

Potomac River

The Potomac River is the second-largest tributary to the Chesapeake Bay and flows almost 400 miles from the mountains of West Virginia into the Chesapeake Bay. The average water flow of the river is 7 billion gallons a day.

Shore erosion in the tidal Potomac River is mostly caused primarily by wind-driven waves and slope processes. Unlike ocean waves, which are largely created by wind, river waves are formed either by water flowing quickly downstream over a drop in elevation.

These waves cut steep banks along most of the shoreline which are interrupted by low-lying areas of marsh and swamp that occupy small stream valleys flooded by rising sea level.

Beaches along these eroding bank sites are generally 6 to 18 feet wide at local mean sea level, with gentle slopes from 4 to 7 degrees. These beaches usually have a limited supply of sand that form them and is veneer over an erosional bench of older material. These sands are mostly derived from bank erosion near the site.

Leesylvania State Park

Leesylvania State Park is on a peninsula formed by two tidal tributaries on it’s north and south, and 800 feet of open Potomac River shoreline on its eastern side. It is the third most visited Virginia State Park with over a half million people visiting it each year.

Like many areas that share shoreline along the Potomac, erosion at Leesylvania Park has been a major challenge to control from the very beginning of this parks development. Since 1984, Virginia has spent over a half million dollars in stabilizing the shoreline.

The areas hardest hit is from Freestone Point Beach in the north to the boat launch area in the south. Until 2018 that portion of the river’s edge had failing gabion, undercut soil, and exposed tree roots. Wave action combined with storm water runoff from upland areas contributed large amounts of fine sediments going into the river.

The eroding upland and falling trees created a hazard to park users, and a plan was put in place to create a Living Shoreline.

LIVING SHORELINE

A living shoreline uses a combination of planting native marsh plants to control sediments and a series of offshore rock structures to serve as a breakwater. This one was designed by the Virginia Institute of Marine Science (VIMS), and it uses a combination of plants, rocks, and sand to protect the parts of Leesylvania that have become unstable. It is a natural system that slows down waves coming ashore, filters water coming in from the Potomac, as well as runoff flowing out of the park into the river. Filtering sediment from water helps keep the Potomac and the Chesapeake Bay clear.

These sills are higher and wider than average rising up above the water at almost 2 feet each with a crest of 4 ft wide to handle High energetic conditions. The shore here at Leesylvania has a very low backshore and it was understood that flooding would still occur during higher water situations. When waves break on these sill structures, they reduce the force of the water enough so that the grassy marsh protects the upland from direct wave attack.

BIORETENTION

During storm events, the rain that falls onto this large impervious parking surface would flow as runoff across directly to the river. As runoff flows across land, it picks up the contaminants, trash, sediments, dirt, and carries them to the storm drains, roadside ditches, and eventually to the nearest downstream waterway. Runoff causes erosion when water falling on and/or running across bare or sparsely vegetated areas dislodges soil and other sediments. When runoff flows over a shoreline bank, dune, or beach, it can erode these landforms from above and create other shoreline erosion problems.

In 2004 the Leesylvania State Park installed two bioretention cells each 135" ft long and 20" ft wide in an area between a large parking lot and the Potomac River to manage it's storm water runoff. Pioneered across the river in Prince George's County, MD, bioretention is the process in which contaminants and sedimentation are removed from storm water runoff by directing the water into landscaped cell depressions that capture and treat the runoff.

LOGGING REQUIREMENTS:

To log this Earthcache: Read the geology lesson above. Answer all six questions posted below. Answers can be sent via e-mail or messenger contacts on my Geocaching profile within a reasonable time. Group answers are fine, but please include the members of the group you are with.

QUESTION 1. BEACH: Potomac beaches have a limited supply sand that form over a veneer of older material. Reach down into the sand and tell me how many inches down it is until you get to dark soil?

QUESTION 2. SILLS: Do the sills and marsh grasses appear to be reducing wave force onto the shore?

QUESTION 3. SILLS: Do the planted grasses appear to be trapping and holding more sediment?

QUESTION 4. LIVING SHORELINE: Did you see any exposed tree roots or undercut soil along the living seashore area on your walk today?

QUESTION 5. BIO RETENTION CELL: How has the placement of this bioretention cell help prevent storm water runoff from eroding the nearby riverbank?

QUESTION 6. Did you see in the park that that wasn't mentioned in the reading that protects the shore from erosion? What was it?

OPTIONAL PHOTO: Posting a photo that readily indicates that you (and anyone else logging the find) are at the location.

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