Indian River Inlet EarthCache

This is an Earthcache – as such, there is no physical cache. Instead after examining the inlet at the posted coordinates you will answer 6 questions. The posted coordinates will take you to Delaware Seashore State Park. Visit this LINK to learn more about park hours and entrance fees. This Earthcache has been approved by Park Management.

An inlet is an indentation of a shoreline, usually long and narrow, such as a small bay or arm, that often leads to an enclosed body of salt water, such as a sound, bay, lagoon, or marsh. This particular inlet connects both the Indian River Bay and Rehoboth Bay with the Atlantic Ocean. There are many inlets like this along the coast of the Delmarva Peninsula, and over time these inlets change. Sometimes inlets are temporary and close up completely, sometimes they migrate miles up the coast through a process called littoral drift, and sometimes an new inlet could suddenly pop up due to a storm surge only to quickly disappear as fast as it appeared.

The natural Indian River Inlet has migrated historically north and south over a 3 to 4 mile area. Maps over time indicates it the inlet was located near the south of the Indian River Bay in 1800, than it gradually moved north over time. By the year 1848 it was located south of Burton Island, and by 1880 it was further up the coast near Cedar Island.

Indian River Inlet, like all inlets tend to be temporary things on the ever changing Atlantic coast. The 1892 inlet formed a big shoal and eventually closed up. At the beginning of the 20th century, the waterway had been reduced to little more than a wet spot in the sand. With no outlet to the ocean, the water in the coastal bays became stagnant, reeking algae bloomed, and reduced salinity was destroying the seafood industry in the bays. Thousands of fish died and the great runs of herring, shad, and other fish in annual spawning runs up the rivers and creeks of the region. Shell fishing grounds were also suffered as a result of the reduced flow in the bay.

Over the next three decades people tried everything from continuous dredging, blowing it open with dynamite, to an small army of local farmers & fishermen armed with hand shovels digging the inlet open. Each time their efforts to create the waterway where short lived, with the sand returning, and the inlet closing back up.

The nearby highway was built with a wood bridge over the inlet in the 1930’s. It was in 1933 that the threat of the constantly moving water way destroying the new road that a plan was formed to make this inlet permanent. In 1936 the Indian River Inlet was stabilized by the Army Corps of Engineers with rock & steel jetties.

A jetty is a breakwater constructed to protect or defend a harbor, stretch of coast, riverbank, or in this case an inlet. A jetty system helps to deepen an inlet channel and reduce required dredging by concentrating and directing tidal currents to optimize scouring action. This is accomplished by confining discharge areas and making flow channels more hydraulically efficient, thereby promoting higher channel velocities. Jetties stabilize an inlet entrance by intercepting the littoral drift and preventing or minimizing deposition in the inlet channel. Jetties also minimize the effects of wave action and crosscurrents on vessels transiting an inlet.

The installation of the jetties has interrupted the littoral drift system affecting a two mile stretch of the Delaware Shoreline. Sediments in the littoral stream tend to deposit and the beach accretes seaward on the south side of the inlet. On the flood tide most of the sand that bypasses the north jetty gets swept into the inlet and gets deposited as a tidal delta shallowing the bay. On the ebb tide sand bypassing the northern jetty gets deposited as an offshore shoal. Most of this sand is permanently lost from the littoral system which results in the north jetty being “sand starved” and open to wave attack that causes serious erosion problems as a result (see photo below). This jetty effect was expected and routine beach nourishment is required on the north side to protect the highway, bridge, and keep the inlet reinforced.

REFERENCES:

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.

QUESTION 1. What is the process that causes inlets to open, close, or migrate up and down the beach?

QUESTION 2. Using the jetty diagram above and observing the jetty at the posted coords, what do you think the reason for the north and south Jetty here not being the same length?

QUESTION 3. Observe the beach on the north side of the inlet. Estimate the distance from the ocean to the bridge. Does it appear to need beach replenishment at the time of your visit?

QUESTION 4. Observe the water in the inlet. Do you see any signs of sediments building up from this inlet?

QUESTION 5. What direction does the water appear to be going at the time of your visit? Is this the EBB TIDE or the FLOOD TIDE?

QUESTION 6. What do you think will happen to this area without continuous beach nourishment on the north side?

POST PHOTO. Posting a photo that readily indicates that you (and anyone else logging the find) are at the location. You do not have to show your face, but the photo should be personalized by you or a personal item with the Indian River Inlet in the background. NOTE: Per newly published Earthcache guidelines, this requirement is REQUIRED to claim the find.

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