How to Renourish a Beach with a Forgotten Past: Indiana Dunes National Lakeshore

A lot of beaches are eroding, basically washing away, because they aren’t getting enough natural sediment to replenish themselves. One reason for this is that we have built hard structures along beaches (like jetties, ports, harbors, and factories) that block sand from being naturally pushed along by waves; sand gets stuck behind these structures and doesn’t replenish the downdrift beaches. One option to combat this problem of beach erosion is called renourishment. When we renourish a beach, we take sand from somewhere else and add it to the beach, making the beach bigger, building habitat and recreational area, and often constructing dunes to help protect the land from energetic waves.

When we renourish a beach, we have to make sure that the new sand is the same as the old natural sand (color, size, texture, etc.) so that the natural habitats and beach shape can remain in equilibrium. So, what do we do if we don’t know what the natural sediment was like because we have already altered the environment? Scientists from Indiana University and the National Park Service set out to answer this question about beaches along Indiana Dunes National Lakeshore.

Indiana Dunes National Lakeshore is flanked by industry and other hard structures that divide the beach into isolated drift cells. Photo Credit: Tom Gill

Indiana Dunes National Lakeshore is on the southern end of Lake Michigan. Naturally, it receives sand that is pushed by waves from northern beaches towards the south. But, as you can see in this picture, Lake Michigan’s coastline has become speckled with hard structures like factories that block this natural flow. Now, sand can no longer migrate down the entire coastline. Instead, it is trapped in isolated “drift cells” between hard structures. These isolated drift cells have altered the natural sediment found along individual beaches, and led to unnatural shifts in beach erosion that destabilize coastal communities, industry, and natural resources of the national lakeshore.

But before beach renourishment can be a viable option to restore these beaches, scientists had to find a way to define what the new sand should look like. Since they couldn’t determine what historical conditions were like, they had to be more innovative. They chose to study the present sediment at nine beaches, which ranged from currently eroding (bad) to currently stable or growing (good). They found that beaches that were eroding had different sizes of sediment than those that were growing. Thus, they were able to determine what type of sediment was best suited to stabilize each beach. They also found out what kind of sediment was best for local marine species. For example, at Central Beach, pebbles that are long and flat are the best choice to restore the natural habitat.

With pioneering studies like this one, we can find out the best way to restore beaches and habitats that have been dissected into drift cells, even if we don’t know what their natural state used to look like.

Do you have a beach in mind that is changing from human impacts? Want to know more about what our options are? Comment below on what you want to know more about!

 

To read the original article by Simon et al. (2016), visit https://link.springer.com/article/10.1007/s00267-016-0750-y

This post was originally written for OpenScienceDB, to help accomplish their goal of bridging “the communication gap between research labs and the public by creating a centralized database of important scientific research taking place around the world.”

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