COASTLINE AND BEACH ANALYSIS

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mangrove

There is a narrow, fine-grained beach at Playa de Fajardo composed of quartz, feldspar, and igneous rock fragments. Most of this sediment has been carried by the Fajardo River. The beach is interrupted in several places by riprap, but erosion does not appear to be severe. Bahia Las Cabezas and Las Croabas beaches are narrow carbonate beaches lying behind a fringing reef which supplies most of the beach material. There are igneous rock fragments in the Las Croabas beach, derived from local sources. Neither of these beaches show signs of severe erosion. From Cabo San Juan to Rio Herrera, the beach sands are carbonate shell material derived from offshore. Minor amounts of quartz, feldspar, and igneous rock material are supplied by local erosion. The beaches are relatively broad and essentially continuous. Rocky outcrops interrupt the beach system at the point west of Rio Juan Martin and Punta La Bandera. At Punta Picua, there is also an interruption of the beach, but from composition and bathymetry it appears that a single beach system is present from Cabezas de San Juan to Punta Vacia Talega. The increases in quartz and heavy minerals near the Herrera and the Loiza Rivers are local additions of sediment by the rivers. The sand bypass from one beach to another in the shoal offshore zone.

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erosion

The composition of the Loiza beach from Punta Uvero to Vacia Talega is strikingly different from the rest of the beach system in having a very high quartz content. This is contributed by the Loiza drainage system. Erosion is marked from the mouth of the Loiza River halfway to Punta Vacia Talega.

West of Punta Vacia Talega there is an entirely different beach system from the Luquillo beach complex and specifically from the Loiza beach. Quartz is almost absent from the beach sands which are 70 to 95 percent calcium carbonate of marine shell origin. The Loiza sands are apparently carried offshore in passing Punta Vacia Talega and only limited amounts return to the beach. Erosion is present west of Punta Vacia Talega. There is a high stabilized dune system behind the beach which is affording some protection to the land area. The beach foreshore is relatively steep. Maldonado Beach is a short, narrow beach between Punta Maldonado and Punta Cangrejos. Erosion is severe on this beach

From Boca de Cangrejos to Punta Chivato the coast is beach plain interrupted by numerous outcrops of eolianite, forming an eolianite shoreline, and several local beach-rock coastlines (Cibuco and Puerto Nuevo). The mouth of Rio de la Plata is a barrier coastline.

The beach sands from Boca de Cangrejos to Old San Juan are a mixture of carbonate grains and quartz. There are about seven separate beaches separated by rock outcrops, but the water depths and composition indicate that there is probably transference of material from one beach to another resulting in essentially one beach system. The addition of a groin at La Concha has interrupted the westward migration of sand. There are sand deposits in deep water (40-50 meters) off Boca Cangrejos which may result from the offshore transport of the beach sands.

The beaches are thin coverings of sand over a rocky shoreline. Erosion at Boca de Cangrejos has threatened the road. The remedial action has been emplacement of rip-rap . There is active erosion at Ocean Park and Isla Verde. There is loss of sand offshore and also windblown into the streets in the Condado area. Although the composition of sand on Isla Cabras is similar to the San Juan beach system, there is probably no transport of sand across the deep entrance channel of San Juan Harbor.

There is active erosion at Ocean Park and Isla Verde. There is loss of sand offshore and also windblown into the streets in the Condado area. Although the composition of sand on Isla Cabras is similar to the San Juan beach system, there is probably no transport of sand across the deep entrance channel of San Juan Harbor.

From Levittown to Rio de la Plata, the beach is dominantly igneous rock fragments with other dark minerals, quartz, feldspar, and carbonate grains. There is erosion at Levittown and Palo Seco. The erosion of sand from behind the beachrock at Levittown is fairly recent and shows the rapid changes in beach position since the construction of the Isla Cabras causeway and the Bayamon canal. This construction has drastically altered the current and wave patters and set up new conditions in the large lunate bays between Isla Cabras and Punta Salinas. Punta Salinas is a tombolo of fairly recent origin that is now being eroded.

Within the last few hundred years there has been a marked retreat of the coastline between Punta Salinas and Rio de la Plata. There are several meanders of the Cocal channels that have been cut off by the retreating beach line. There is severe erosion just west of Punta Corozo that has been partially controlled by riprap to protect the highway.

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From Laguna Tortuguero to Penon Afuera, the coastline is beach and eolianite. More of the coast is eolianite than to the east. The sands from Punta Chivato to Rio Manati are carbonate with some quartz grains and igneous rock fragments. The material is from offshore production by marine organisms and weathering of the eolianite. There are numerous lunate bays, formed by erosion of the land when the eolianite is breached, and numerous examples of tombolos, where the sand connects remnants of eolianite to the receding shoreline. In many of these, there is no obstruction to the passage of sand behind the eolianite. Most of the beaches are thin sand deposits over a rocky lower foreshore.

During winter storm periods these sands may move offshore temporarily. The Manati River carries large amounts of igneous rock material, dark minerals and magnetite. The beaches to the west of the river mouth are dominated by these minerals. There is a slow decrease in these grains and an increase in carbonate material toward Jarealito. Although the beach materials have been transported behind the eolianite, many of the tombolos are now stabilized by the growth of vegetation, and sand is no longer passing across the tombolo.

Between Tres Hermanas and Jarealito, the beach is dominantly carbonate with some igneous rock fragments. From Rio Arecibo west, the beach is quartz, feldspar and igneous rock fragments in roughly equal portions. On some of the beaches (Arecibo, Quebrada Seca West) the magnetite content is very high. Both the Arecibo and Camuy Rivers carry sediments to the beach system.

Near Islote, part of the beach sands are being lost from the system by wind erosion . The sands are being incorporated into dunes behind the beach, and evidence of recent activity is shown where the sand has blown over the vegetation.

The coastline west of Penon Afuera is secondary type resulting from wave erosion of a rocky coast.

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The beach at Bellaca is a small local sand accumulation or pocket beach. Most of the beach material is carried to the area by the quebrada. The Guajataca beach is quartz, feldspar, and igneous rock material carried to the area by the Rio Guajataca. It is isolated from the other beaches by rocky headlands . The beaches east of Isabela are generally narrow, thin veneers of sand over a rocky shoreline.

From Del Toro beach westward, there is a thick and wide dune system behind the beaches which probably supplies most of the beach sands by landward erosion. There is no permanent drainage system into this part of the coastline, but the sands are dominantly igneous rock material, quartz, and feldspar. Carbonate grains make up only a small part of the beach sand. There are numerous rocky headlands interrupting the beaches, but there is probably lateral migration of the sands in the nearshore region.

The dunes behind the beaches have been extensively mined for sand, and in places (Sardina) the beach sands have been removed. The beach at Punta Jacinto shows the wide and thick accumulation of sand that lies in front of the vegetation covered sand dunes. West of Jobos beach, there has been major removal of the dune sands. Both the composition of the beach, and the presence at the lower part of the beach of beachrock outcrops suggests that the major source of beach sand is the dune system.

Punta Borinquen and Crashboat beaches are isolated beaches bounded by rocky shoreline. The beach is continuous from Aguadilla to Punta Gorda, and the coastal type is beach plain.

There is erosion from Rio Culebrinas to Punta Gorda. The beach sediments are approximately equal parts carbonate shell material, quartz and feldspar, and igneous rock fragments. Sediments from a large drainage basin are carried to this part of the coast by Rio Culebrinas and Rio Grande. There is strong littoral drift to the southeast, but no evidence of severe erosion except near Ríncon.

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The Corcega beach sands are carbonate, quartz, and igneous rock fragments with minor amounts of feldspar. It is a fairly broad beach with a steep foreshore face. The beach terminates at Punta Cadena, where the shoreline is rocky. Sampling off this point indicates that much of the sand is moving offshore at Punta Cadena. Some of this sand bypasses the point and is added to the Añasco beach system.

The north end of the Añasco beach is calcium carbonate with quartz, feldspar, and igneous rock fragments. There is an offshore source of calcium carbonate shell material south of Punta Cadena. The carbonate content decreases southward until at Mani beach the dominant component is igneous rock fragments with quartz and feldspar and some carbonate grains. The beach terminates at the land fill of the Malecon industrial site. There is erosion from E1 Puente to Mani beach north. The flooding associated with hurricane Eloise moved large amounts of river sand offshore. Shoreward transport of this sand has (temporarily) halted erosion at E1 Puente. During normal flow conditions, most of the Añasco River sand size sediments are trapped in the estuary. However, during floods and high rainfall these sands are carried offshore and some of this material may join the beach system. There is relatively little offshore movement of the sand and most of it is accumulating at the Malecon landfill site and offshore from Mani beach south. The accumulation at the Malecon landfill is a potential sand source. Mayagüez beach is composed of igneous rock fragments, magnetite, and other dark mineral grains, and minor amounts of feldspar grains. The mineralogy is very different from the Añasco beach system. The deep water of the Mayagüez Harbor entrance blocks transport of sand from the Añasco system to Mayagüez beach.

There is erosion along the southern half of Mayagüez beach. Riprap has been added to long stretches for protection until the coastline is no longer beach. This has slowed the loss, but has also shifted the erosion to another part of the beach until riprap now extends to the Guanajibo River. The September 1975 flood made major alterations to the beach and ripped out both highway and riprap . Prior to the flooding, the severity of the beach erosion was shown by the undermining of homes on the beach. The flood carried large amounts of sand offshore. Some of these sands may return to the beach system, but most will be covered by the marine silts that are the dominant sediment beyond the three meter depth contour.

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Ostiones

Between Punta Melones and the Parguera forests the coast is beach plain with short stretches of rocky wave erosion coast at Cabo Rojo and Punta Molino. There are short expanses of mangrove coast on the west and east side of the Cabo Rojo tombolo and west of Playa Sucia. From a point just east of Punta Molino to Punta Montalva, the coastline is dominantly mangrove . There are areas of striking growth of land contributed by the spread of mangrove, and several former beach lines can be seen as much as half a kilometer inland.

E1 Combate beach is quartz and calcium carbonate sand. There is no evidence of strong erosion. Punta Aguila separates Combate beach from Aguila beach which is dominantly calcium carbonate with minor amounts of quartz and igneous rock fragments. Considering the change in composition and the prevailing pattern of longshore drift, transportation of sand between the two beaches is probably of limited extent. Cabo Rojo beach is a small pocket beach at the base of the limestone cliffs. It is composed of carbonate and quartz grains. Cabo Rojo is an outlier of the limestone forming the coast and is connected to the mainland by the deposition of a sand spit which joins the two. This has been used as an example of a tombolo. Playa Sucia is a carbonate and quartz beach that gets its name from the unique circulation patterns in the bay between Cabo Rojo and Punta Molino. As the surface currents move westward along the south coast of Puerto Rico, part of the flow passes Cabo Rojo and continues into the Mona Passage. Part of the flow is diverted into the bay and carries surface debris to Playa Sucia. The bay contains large quantities of sand which are being moved southwest past Cabo Rojo. Since the longshore drift is south from Punta Aguila, this sand is being moved out of the beach system and is a potential sand source for offshore mining.

From Punta Molino east to Punta Verraco, there are only small pocket beaches at the base of limestone cliffs or isolated in a mangrove coastline. There is no evidence of communication and passage of sand from one to another of these beaches. All of the beaches are composed of calcium carbonate grains derived from erosion of the limestone cliffs and from the shells of marine organisms living offshore. The largest of these beaches are Montalva, Pardas, Cana Gorda, and Ballena.

At Parguera there is a tidal flat coastline behind fringing mangrove. The land immediately behind the coast is a low range of limestone hills that are the southern limb of a syncline. Isla Magueyes and Isla Matei are outcrops of this limestone. Visual observations, seismic surveys, and collected data show that the shelf south of La Parguera is underlain by the same limestone, and it has been suggested that the lines of offshore reefs may be localized by outcrops of the southern flank of the limestone syncline,

Both Magueyes and Matei are surrounded by fringing mangrove . Bahia Fosforescente is also bounded by mangrove. From Parguera east, there are low tidal flats and Salinas behind the mangrove shoreline.

East of Montalva the coastline is formed by wave erosion of the southern limestone platform. The coast can be generally classed as secondary wave erosion made irregular by waves. There are numerous small pocket beaches of sand and gravel at the base of the limestone cliffs, with no apparent ~connection to one another.

Playa Santa is a pleasant bathing beach easily reached by car from Ensenada. The area is rapidly being built up by construction of a condominium and an urbanization of small houses. Pardas is bounded by national forest and access for the public is difficult. Several aerial observations suggest that surface oil may be carried to this beach from Guayanilla.

Caña Gorda beach is a public balneario with a hotel at the east end, and is a popular and pleasant beach area. Ballena is relatively easy to reach by the dirt road that continues along the coast past Caña Gorda. This is the only beach of this group that shows signs of erosion.

The small pocket beaches at the base of cliffs west of Ballena are composed of calcium carbonate sands. The beach at Punta Ventana is different in composition. It is a mixture of calcium carbonate quartz, and dark minerals and igneous rock fragments. The Yauco River once flowed to the coast at Punta Ventana and cut a deep submarine canyon in the shelf to the south. The quartz and dark minerals were transported to the area from the interior by the river and are relict sediments. Since the course of the river has been diverted, probably by faulting, the only modern sediments being contributed are calcium carbonate. Playa Ventaña is virtually inaccessible to the public. The road to the beach runs through lands owned by Central San Francisco and signs on two locked gates warn of prosecution of trespassers.

From Punta Verraco eastward, the coastline and beaches are drastically different. The coast is a low lying alluvial plain except for a short stretch between Tallaboa and Punta Cuchara. Here the coastline is wave erosional and fringing reef. The rest of the coastline is either beach plain or mangrove.

The composition of the sands and distribution of beaches is very different from the preceding area. Guayanilla beach is dominantly igneous rock fragments with quartz and dark minerals. Tallaboa beach is dominantly igneous rock fragments with some carbonate grains and Punta Cuchara is of dark monomineralic composition with igneous rock fragments. The rocky shoreline between these two beaches has only small and isolated pocket beaches.

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The beach at Punta Cuchara is being eroded and a large amount of the land behind the beach has been removed. The low beach to the east, Matilda Beach , is a free sand removal area and a garbage and junk dump site. It is one of the worst looking stretches of coastline in Puerto Rico. From Punta Carenero east to Punta Petrona, there is almost continuous beach plain interrupted by mangrove eroding alluvial plain, and rock riprap. More than fifty percent of this coast is suffering erosion. The materials range from sand to gravel and are dominantly dark minerals and rock fragments Several of the beaches have especially high concentrations of magnetite.

The coastline from Jauca to Playa Salinas is a combination of beach plain and mangrove. East of Salinas there is considerable mangrove coast. The Cayos Caribe are small mangrove islands that are behind a fringing reef coastline. From Las Mareas eastward the coast is dominantly the result of wave erosion of the relatively unconsolidated alluvial plain material that lies south of the central mountains. There is extensive development of narrow beaches at the base of wave cut cliffs. From Arroyo eastward, the coastline is dominantly beach plain.

The beach materials are fragments of igneous rock material with magnetite, dark minerals, and some quartz and feldspar. There is considerable increase in the amount of quartz and feldspar east of Las Mareas and the beach at the mouth of Rio Manuabo is almost entirely quartz and feldspar composition. There is very little calcium carbonate material except at Libre Florida.

Much of the beach material in this part of the Island is gravel-sized . The gravel appears to be residual alluvial plain material left in the surf zone as the alluvial plain is cut back by wave action on many of the beaches.

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Las Mareas

The coastline from Punta Tuna to Naguabo is an alternation of rocky headlands that have been partly shaped by marine erosion and valleys of alluvial material that have been worked on by wave action and marine deposition to form broad beach plains. North of Punta Lima the coastline is mangrove coast, rocky headlands, and a few small beach plains and pocket beaches.

The eastern end of the island is bordered by a shallow shelf with abundant coral and marine organisms forming carbonate sands. As a consequence the beaches are a mixture of calcium carbonate grains from offshore and quartz and feldspar and igneous rock material and dark minerals from the land area.

Although the composition of the beaches is similar, physical boundaries formed by rocky headlands divide the coast into eight distinct beaches. There may be limited transfer of sand from one beach to another in the offshore zone, but they are distinctly separated physically.

Punta Tuna beach is a beautiful coarse carbonate sand beach with some quartz and igneous rock material that lies east of the Punta Tuna lighthouse . The land adjacent to the beach is pasture for large herds of cattle, but the owners have provided access to the beach.

Punta Toro beach is quartz and carbonate with some feldspar. The quartz and feldspar is derived from the plutonic outcrops north of the beach.

From Quebrada Honda to Guayanes there is a series of pocket beaches and some relatively long stretches of wide beach composed of quartz and feldspar, with some carbonate and igneous rock material, Guayanes beach, at the north end of this system is especially rich in magnetite. The transport of sand in this system is now interrupted by the deep channel and jetties constructed as part of the Yabucoa Harbor.

The Candelero beach system starts with a group of small pocket beaches between Punta Guayanes and Punta Fraile. There is a continuous beach plain from the Palmas del Mar marina at Punta Fraile to Morro de Humacao. The composition is dominantly calcium carbonate. There is erosion at Punta Candelero and for a short distance north.

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The coastline encompassed by the naval base was inaccessible, and not examined.

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