Beach renourishment

[greenroomsurfer]

Here is another video for the non-believers. http://www.cccturtle.org/higherground.php

 

[BeachSiO2]

beacheart, help me understand how adding more sand to extend the beach helps a gulf front homeowner. I don't see how. With a decent size storm, like any of the ones which hit us in 2004-2005, the beach would be covered with sweeping water, hitting at the dunes or seawalls. A large storm will still remove that additional sand used to widen the beach, in my opinion. Do you see that differently?

Let me just chime in on the scientific side of here. Beach restoration that was conducted in Walton County is not just about wider beaches. It also involves the construction of an additional dune, and the raising of the existing beach in a stair stepped formation. In short, there is about 80 cubic yards of sand placed per foot of beach. Here is how all three sections of the project will function prior to and during a storm.

First, we must remember that a wave will typically break when it reaches water depths that are about 1.28 times it's size. In other words, in 1 foot of water the maximum wave a size can be is .78 feet. Keep in mind that the majority of the energy of a wave is released when a wave breaks. On to the three parts and I have included the actual beach design graphic for the western portion of Grayton Beach where the four or five houses are so that it may become more clear.

How does a wider beach help? First, after a project is constructed a portion of the placed sand immediately begins to move offshore and decrease the offshore water depths. This offshore equilibration is expected and accounted for and is included in project design, note the location of the "equilibrium grade on the graphic. Some of this sand will migrate all the way out to the sand bars thus raising their height (decreasing water depth) and now larger waves break further from shore on that sand bar. For waves that make it to the beach, that beach is now 75-100 feet further offshore, thus reducing the amount of wave energy that makes its way to the higher areas of the beach and dunes.

How does a higher beach help? This is where the storm surge is mitigated. The constructed beach elevation will be about 3-5 feet higher than the beach in 2007 as you can see in the attached figure, and in the offshore areas, even more. In the likelihood of an increased water level from storm surge, the beach will be about 6 feet higher than a normal high tide. So storm surge will have to be higher than +6 just to overtop the beach and get close to the upland area. But in reality it will have to be even higher to be able to form a wave. So, what once could be overtopped with about a 4-5 foot storm surge will now take 6-7, and 8 feet to reach the dune. We did not have storm surges of this size in either 2004 or 2005.

How does the dune help? In the possibility that a storm reach sustained storm surge levels of more than 8 feet than the constructed dune will be impacted. that dune will be approximately 20-25 feet wide at the top, and about 35-40 feet in width total. Plus it's elevation will be about 12 feet higher than mean high tide elevation. This is designed to protect the toe of the existing dunes. Currently, there is only a little toe protection in many areas and once the water hits the toe of the current dune it can wash out the top.

So, yes a storm can come along and impact an area and impact these types of projects. This is no different than a levee system. A level of risk is identified and then a design is developed based on protection afforded. This design is designed to mitigate impacts for a Category three hurricane. In other words, this design would be greatly impacted but it would take a storm greater than a Cat 3 to remove more sand than was placed. This was further exemplified in Pensacola with Ivan in 2004. Based on post-storm measurements, there was more sand left within the dune, beach and nearshore area after Ivan than when they built the project. The Walton County designs are very similar.

Since SJ has started giving .03, I am giving a buffalo nickel.

 

[scooterbug44]

Nice graphic, but in the last 5 years, I've seen tropical storms and hurricanes of less than Category 3 take out the entire area you've identified as new "finish grade."

Just my Sacajawea! ;-)

 

[BeachSiO2]

Nice graphic, but in the last 5 years, I've seen tropical storms and hurricanes of less than Category 3 take out the entire area you've identified as new "finish grade."

Just my Sacajawea! ;-)

Maybe the intermediate stair step, but not the entire 80 cubic yards per foot of beach. I know, I helped analyze the data. What you likely saw was a lower beach that was in the area of about +5 feet in elevation at the toe of the dune. That lower beach was submerged and allowed for 2-3 feet waves impact the toe of the dune. Once the toe of the dune was impacted the top fell. I compare it to California cliff failures.

Voila, that is why you see a new designed beach that has a higher back beach area and a substantial amount of sand placed at the toe of the existing dunes. By the way, the beach was measured on 1000-ft increments both in 2004 and 2005 after hurricanes and there are no areas that lost 80 cubic yards of sand per foot of beach which is what the design is. Here is a link to the final report for those who may be interested.

http://protectwaltoncountybeaches.com/pdf/WaltonCountyPostDennisAssessment.pdf

My follow-up peso.

 

[Smiling JOe]

I appreciate the additional info, BeachSi02. I believe I understand the process. What I have witnessed first-hand from the 2004-2005 storms, which didn't actually directly hit this area, was a massive east/west push. It wasn't the wave action that hurt SoWal as much as it was the westerly push. That alone seemed to remove the sand from the beach and the base of the dunes. After that sand was removed, the waves were hitting, but only at the foot of the dunes. It was the westerly push, not the waves, which seemed to dismantle the beach walkovers from my observations. This push continued for more than 12 hours during each storm, and remember, we didn't even get hit by the storms.

What next? So we get hit a direct hit with a Cat 3 Hurricane, all the added sand is now removed. Fema steps in and pays for the redo, and we continue to fight a never ending battle against mother nature. Why don't we take notes from mother nature, and work around her? What's wrong with that idea? It has been stated on here that the beach nourishment is beneficial to everyone. I fail to see that. The dune systems will sluff, and smaller storms will push more sand on shore, replacing the sand on the beach. It just won't be immediately, but we know that all good things take time. We people tend to want to place things, pets, and people in a no-grow box, as soon as they get perfect. We think that our lives will be perfect when we do this, this, this, but the truth is, life is already perfect -- We just clutter it with layers hiding the perfection.

 

[BeachSiO2]

I appreciate the additional info, BeachSi02. I believe I understand the process. What I have witnessed first-hand from the 2004-2005 storms, which didn't actually directly hit this area, was a massive east/west push. It wasn't the wave action that hurt SoWal as much as it was the westerly push. That alone seemed to remove the sand from the beach and the base of the dunes. After that sand was removed, the waves were hitting, but only at the foot of the dunes. It was the westerly push, not the waves, which seemed to dismantle the beach walkovers from my observations. This push continued for more than 12 hours during each storm, and remember, we didn't even get hit by the storms.

What next? So we get hit a direct hit with a Cat 3 Hurricane, all the added sand is now removed. Fema steps in and pays for the redo, and we continue to fight a never ending battle against mother nature. Why don't we take notes from mother nature, and work around her? What's wrong with that idea? It has been stated on here that the beach nourishment is beneficial to everyone. I fail to see that. The dune systems will sluff, and smaller storms will push more sand on shore, replacing the sand on the beach. It just won't be immediately, but we know that all good things take time. We people tend to want to place things, pets, and people in a no-grow box, as soon as they get perfect. We think that our lives will be perfect when we do this, this, this, but the truth is, life is already perfect -- We just clutter it with layers hiding the perfection.

I agree that the fact that we were on the east side of the impact area that there was a strong westerly flow of water and sand. My point was that the height and width of the beach were both less than what is in the proposed project and thus I was trying to offer additional information on how you can't compare the beach condition during Dennis to the beach condition after a project. Keep in mind it didn't take long for the storm surge to submerge the existing lower beach which allowed the east-west push to directly impact the toe of the dunes. That beach was about 3-5 feet lower and 75 to 100 feet narrower than the designed beach. Like I said the construction volume is about 80cy/ft of beach which equivalent to 4 of the huge off-road dump trucks squished 1 ft wide.

The second part of your email is the political side of the equation. This is where risk comes into play and a decision by a community and community leaders on what level of risk they are willing to live with. I just wanted to outline how a project works and that it will make a difference in a storm to an upland area, whether is a house, a road, etc. There has been very good research done in this area by Bob Dean at UF showing correlation between distance to the water during a storm and damages to an upland area. I will try and track down a copy of the paper and have it added to the www.protectwaltoncountybeaches.com website for anyone's interest.

 

[Smiling JOe]

I understand that it is a lot of sand, but mother nature can move it in one swift swoop, while it may take us the entire summer to move it with heavy yellow equipment.

Can you explain how the rare Coastal Dune Lakes of Walton County will be affected by adding both elevation and width to the beach? Seems to me that doing such would likely cut off the lakes from the Gulf completely, unless we have a major hurricane.

 

[BeachSiO2]

I understand that it is a lot of sand, but mother nature can move it in one swift swoop, while it may take us the entire summer to move it with heavy yellow equipment.

Can you explain how the rare Coastal Dune Lakes of Walton County will be affected by adding both elevation and width to the beach? Seems to me that doing such would likely cut off the lakes from the Gulf completely, unless we have a major hurricane.

I am not arguing about what Mother Nature may do, because she can do a lot with one storm. I will say though that Mother Nature did not remove all of the sand from the Pensacola Beach project during Ivan and that was just about a direct hit from a Cat 3. The reality is that if a storm of the magnitude that it would take to remove that amount of sand were to hit South Walton or slightly west of us, then we will likely have even greater impacts around the low lying dune lake areas and properties north of 98.

There are buffers and set backs from each coastal lake outfall that is affected and no sand will be placed in front of the outfalls. At this time the project is designed to be built on both sides of Oyster, Draper, Alligator, and Eastern.

 

[Smiling JOe]

With as much as the wind seems to blow from the east, pushing sand around, I'm curious to know how far outside of the lakes are the set backs. We saw what happened with Easter Lake when sand was placed east of the outflow.

I do agree that storm surge from a direct storm hit will likely affect more inland owners than Gulf front owners, which is why I don't see why so much money is being spent on the beach, which is ever-changing.

It is good to have a specialist, like you, to explain some of this nourishment process, in plain language. Thanks.

 

[BeachSiO2]

With as much as the wind seems to blow from the east, pushing sand around, I'm curious to know how far outside of the lakes are the set backs. We saw what happened with Easter Lake when sand was placed east of the outflow.

I do agree that storm surge from a direct storm hit will likely affect more inland owners than Gulf front owners, which is why I don't see why so much money is being spent on the beach, which is ever-changing.

It is good to have a specialist, like you, to explain some of this nourishment process, in plain language. Thanks.

It depends on the lake and there has not been any final decision made. It is still being discussed with the permitting agencies, but the analysis for the design included the variability of the outfall location. It is a major point of discussion with the project, as it should be.

Like I said, its all about risk. How much damage would it due to the community from a physical, social, economic, etc. point if nothing is done, versus the costs (not just monetary) if a project is built. Hopefully, those who will be affected will participate in the process and make their voices heard.