Background on Beach Erosion, Groins and Beach Nourishment - great read

I have spent a lot of time researching what we can do to Save Our Beach - Sargent Beach is truly a great place and obviously worth saving.  

A beach is a very complex system - and always changing.  So there is no one solution that will complete solve beach erosion. What it really takes is an ongoing plan and responses to ensure we have the beach forever.  After this initial project is complete - our efforts need to focus on that long term plan. 

The chart above shows all of the different impacts on a beach.  The arrows show that beach sand goes both out to sea and along the shoreline (littoral drift).  Sargent has a lot of issues with our beach system.  First - sand from rivers has been interrupted and will hopefully be fixed when they open the San Bernard.  Second - we have no dunes for sand to replenish during big storms. And third - the fact that our sand sits on clay causes more extreme erosion. 

I found the American Shore and Beach Preservation Association that has a huge amount of information. They basically bring science and policy together to try and protect beaches across the country.  They track what projects are working and what was done that did work. It is amazing - note that I studied coastal engineering in college so I geek out on this stuff. 

Why do beaches erode - The simple answer is they do not have enough sand. However, the causes are different in different parts of the country. 

• Beaches are sand starved when something blocks the flow of sand from the river (San Bernard). Other beaches often lack sand because inlets or navigation projects interrupt sand’s along-shore movement. (our sand moves east to west)
• All beaches suffer from storms and other natural events that cause erosion. Things as different as storm-driven waves or a simple change in an offshore sandbar may cause one coastal area to lose sand while another area gains. 

What can be done about erosion?

• Structures: There are two kinds that “draw the line” in the sand – literally. Seawalls run parallel to the shore to protect the property behind them. Unfortunately, they don’t add sand to the system. Other structures (groins and jettys) run perpendicular to the shoreline and keep sand from moving down the beach. They can work well only when sand is already being added to the beach. (open the flow of the river and do a beach renourishment)
• Beach restoration: Adding sand to the beach to replace what’s been lost is the closest we’ve come to solving the problem. Coastal scientists have years of experience with beach restoration projects and have learned that adding sand in the right quantities, properly engineered and maintained, can make a beach last forever.

So what is a Terminal Groin that they are installing at Mitchells Cut and why will that help?

• Beaches adjacent to tidal inlets are often subject to accelerated erosion and much larger scale fluctuations in the shoreline compared with beaches away from inlets. Terminal groins placed at inlets can limit the loss of sand into the inlet and moderate large-scale fluctuations of the shoreline near the inlet.
• It is recognized that inlet delta systems are natural conduits for bypassing sand from updrift to downdrift shores and that a terminal groin will reduce the amount of sand entering the inlet by reducing transport from the updrift shore. 
• The terminal groin should be long enough to maintain enough sand up-drift of the groin to establish the desired storm protective beach profile and in addition be able to hold an extra amount of sand in anticipation of drift reversals that would otherwise temporarily expose homes and infrastructure to storm damage. 
• The ASBPA concludes that terminal groins can be beneficial to control erosion on nourished and unnourished beaches and reduce losses of sand to coastal inlets. Terminal groins can control large-scale fluctuations of the shoreline and protect homes and infrastructure. Although downdrift and inlet shorelines can be adversely altered by the reduction in sand movement caused by a terminal groin (sorry Matagorda beach), the overall positive effects of these structures typically outweigh negative effects that can be mitigated by other actions

Finally a great article on how beach nourishment project works - 

• Storms erode and transport sediment from the beach into the active zone of storm waves. Once caught in the waves, this sediment is carried along the shore and redeposited farther down the beach, or is carried offshore and stored temporarily in submerged sand bars. Periodic and unpredictable hurricanes and coastal storms, with their fierce breaking waves and elevated water levels, can change the width and elevation of beaches and accelerate erosion: 
• Longer lasting storms, which give the waves more time to attack the beach, cause more erosion and sediment transport than fast-moving storms. 
• Very intense storms create higher winds and larger waves, inducing more erosion than less intense storms. 
• After storms pass, gentle waves usually return sediment from the sand bars to the beach, which is restored gradually to its natural shape. Sometimes, however, sediment moving along the shore leaves the beach system entirely, swept into inlets or taken far offshore into deep water where waves cannot return it to the beach. This causes the shoreline to recede, or move farther landward. Over time, these processes – combined with sea level rise – produce larger waves that break farther landward. In flat coastal areas, beach erosion and shoreline recession can have dramatic consequences to people and property.
• Beach nourishment projects are designed and engineered to work like natural beaches, allowing sand to shift continuously in response to changing waves and water levels. Coastal engineers may decide to place beach fill as underwater mounds, directly on the beach, as dunes – or all three. This sand, once placed, is redistributed gradually by natural processes affecting the beach system. Ultimately, the wider, nourished beach, which slopes gently downward below the water, and the taller sand dunes protect the shore by acting as naturally protective buffers. 
• The gradual slope of the nourished beach causes waves to break in shallow water as they begin to feel bottom. As water rushes up the beach, wave energy dissipates. 
• Water running back down the beach redistributes sediment, which is deposited in deeper water or moved along the shore. 
• These sediments often create an offshore bar that causes waves to break farther offshore, again dissipating wave energy, and thus protecting people and property behind the beach.
• To ensure that a nourished beach continues to provide protection and mitigate the effects of hurricanes and coastal storms, the project must be supplemented with additional quantities of sand, called periodic renourishment, as needed. 
• Also note - the project is designed to flatten out and move out into the water - this softens the waves and keeps them from damaging the coast later on. 

So - in order to restore the beach we need to stop the sand from moving out to sea through the groin and breakwater, we need to increase the supply of sand coming from the San Bernard and we need a beach renourishment done to complete the project. 

Long term, then we need a plan for periodic renourishment and expansion of the breakwaters if the beach isn't holding.  A comprehensive long term plan is the next phase we have to push for.