Field Observations and Data Interpretations

Data Interpretations

The coastline is emergent. The beach is above ground due to tectonic uplift or a decrease in the elevation of sea level. Tides can erode the beach and take away sand. Sand can also be brought in and deposited in the berm during high tide. The longshore current moves parallel to the shore and brings sediment into and out of the beach system. Beach sand will move forward or backward depending on the direction of incoming waves. I think the barrier bar will be moved near the mainland if sea level continues to rise. Seawalls, groins, jetties, and breakwaters can be built to stabilize the position of the shoreline and the width of the beach. People could also deposit large sums of sand on the shore.

High-density construction and the increase in population will kick out and destroy preexisting natural ecosystems. Pollution can also occur from the high volume of people and the work they do in the area. People could plant appropriate vegetation on the beach to combat against erosion. Breakwaters could be used to trap sand and then be used in conjunction with projects that add sand to the shoreline.

Berm

Based on the width of the berm, it is characteristic of a winter berm. The primary natural process responsible for the deposition of sand on the berm is wave action via the longshore current. Coastal straightening is present on the berm. I can determine the extent of the high tide because of the wreck line. When digging a hole into the upper part of the berm, there is evidence of deposition through bedding planes and the berm, itself. The average grain size of the berm sediment ranged from 0.5mm to 0.35mm. The windspeed was 20.3mph coming from the NE. There were no types of vegetation on the berm. The width of the berm was 69ft.

Data Interpretations

Berms typically undergo a seasonal transformation from a “summer” berm to a “winter” berm. Summer berms are usually well-developed and contain vegetation while winter berms are generally flatter and contain less vegetation. With increased storms and wave heights along with a change in wave and wind direction, beach berms tend to erode, lowering the beach and the berm’s width. In spring and summer months, waves are calmer and sand slowly returns to the beach and berm, creating a wider berm.

I’d recommend building breakwaters, groins, jetties, and seawalls to mitigate the effects of wave erosion along the beach. A large amount of sand could be deposited to maintain the beach’s size. Seawalls could be built as well as groins perpendicular to the shoreline to help mitigate the effects of wave erosion along the beach. A large sum of sand could also be brought in and deposited on the beach to combat wave erosion.

A built seawall can displace the beach that it is built on and prevent natural landward migration of an eroding beach. When waves hit seawalls, they are reflected back to the ocean and take sand away. Groins transfer erosion from one part of a beach to another. Break walls can drastically change the profile of a beach when the longshore current is interrupted.

Dune Ridge

The beach side was the primary dune being eroded and the seen erosional features were erosional scars. Cross bedding was present in the dunes, indicating deposition. The dominant types of dune grasses along the crest of the dunes were American beach grass and sea oats. Dune grasses protect dunes from wind and wave erosion. Primary dune grasses have extensive roots to help keep them in place and strive in the harsh environment. The average grain size of the dune sediment ranged from 177mm to .35mm. Sand from berms are the immediate source of sand for the primary dunes. The wind speed and direction at the dunes’ crest was 10.3mph from the NE. The wind speed and direction behind the dunes was 8.9mph from the NE. The dune size and shape gets significantly smaller when moving from the beach side to the lagoon side of the barrier system. The width of the dune field was 326ft. The distance from the last dune to the lagoon’s edge was 157ft.

Data Interpretations

Dunes absorb the impact of erosion by wind and water while preventing or at the least, delaying the flooding of inland areas and damage to inland structures. Dunes also supply sand to eroded beaches during storms. The dominant marsh grasses are intolerant to salt which makes them not commonly found in the dunes. The dune sediment is transported by the wind which makes it well sorted and have a high degree of rounding. The sediment found on the beach face and berm does not experience the same degree of being blown about by the wind as the dune sediment does. I would not recommend the removal of the dunes in order to build condominiums because dunes protect the interior land from flooding. A strong defense system against water and winds is taken away by the dunes being removed.

Lagoon

The size of the lagoon side of the barrier was tight and compact. The area was very dense and there was not much variation in the vegetation. Streams and wash-over events are responsible for the transport and deposition of sediment in the lagoon environment. The tide does not affect the lagoon in the same way that it affects the beach face. There are wind forced tides. The windspeed and direction within the lagoon area was 11.4mph from the NE. The dominant type of vegetation present were phragmites. The salinity of the lagoon water was 4ppt.

Data Interpretations

The lagoon environment is protected from the ocean by barrier islands while the beach does not have such protection. The washover fans are created along the backside of the barrier bar system when a tidal surge associated with a storm causes water to flow across a barrier. I think flooding from the ocean side into the lagoon would destroy the lagoon’s ecosystem because the salinity values of the ocean are much higher than the salinity values of the lagoon. The lagoon’s ecosystem is accustomed to low levels of salinity while the ocean has much higher levels of salinity. A drastic shift in salinity levels could ruin all the processes occurring in the lagoon.

General Questions

The total width of the barrier bar system is 919ft long. The grain size increases moving westward. The beach face and berm have smaller sediment grain size while the dunes and the lagoon’s sediment sizes are larger. The sediment found on the beach face is moderately sorted. The sediment found on the berm is well sorted. The sediments found on the dune are well sorted. The sediments found on the lagoon are well sorted. The vegetation became more varied, thicker, and more dense from the beach face to the lagoon. The salinity of the soil is the reason for the richer vegetation on the lagoon. Plants break the impact of erosion by water and reduce runoff erosion. Plant roots hold sediments in place and stabilize the areas they are planted in. I would like to see the native vegetation planted on the lagoon side of the Back Bay Wildlife Refuge system. The barrier system could stay in better shape if breakwaters were built to combat erosion.

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