Coastal study sites east coast Puerto Rico

The east coast of Puerto Rico is characterized by short period waves (3-5 seconds) approaching from the east and northeast. High amplitude waves occurred during storm events and the coast was exposed to the direct path of major tropical storm systems. The coast is bordered by a broad carbonate platform with many natural barriers such as coral reefs. A well developed cay system is present from Fajardo to Vieques Island. These act as natural barriers that protect the shore from wave impact. Few hardgrounds and no eolianite deposits exist on the platform. Sand deposits are larger than on the north coast of the Island. Submarine canyons are located on the outer shelf that do not affect the east coastline.

Morphologically, the coast differs from the north coast in that it is less indented and has broader headlands . Large rocky headlands are located between broad alluvial plains. Plutonic, volcanic and sandstone rocks form the headlands. Beach systems are in some areas at the base of the cliff. Others were located among rocky shorelines. Extensive alluvial plains were related to the major river systems at Naguabo, Humacao and Yabucoa.







The 9th field trip will be to sites on the east coast of Puerto Rico, starting at Yabucoa











East Coast Sites

North and south beaches at Yabucoa Port
Punta Santiago, Humacao
Rio Blanco, Naguabo











22 apr 2003 trip

North and south beaches at Yabucoa Port

Net accretion was measured in all stations from south Rio Guayanes to Yabucoa Port from 1969 to 1987 with major accretion in the south of the beach. Shoreline was added from terrigenous sediments coming from Rio Guayanes, Cabo de Santiago and Quebrada Laja that was then transported to the south by currents.

Most stations at Yabucoa north from 1969 to 1972 accreted, except very low erosion rates were measured at stations 10 and 11. There was still accretion for stations 1 to 5 from 1972 to 1979 but stations 6 to 11 had low to moderate erosion. Erosion was related to the construction of the facilities of the Oil Sun Corporation that caused many modifications to the coast with the building of groins, jetties and dredging activities of the port.

All stations had accretion from 1979 to 1985. Sand added to the beach was caused by the stabilization of the beach itself generated by the structures and could be related to the decrease in storm occurrence during this period.

Very little net accretion was measured on stations in the beach located south from Yabucoa Port from 1962 to 1987. However, all stations had low erosion rates from 1962 to 1977. As at stations 10 and 11 located at Yabucoa north, erosion was caused by high amplitude waves from the passage of tropical storms in the area. According to refraction plots, long period waves (8 to 11 seconds) approaching from the southeast and northeast caused high wave energy concentration on these stations, except for waves with a period of 14 seconds where high energy concentration occurred to the north. A shift from erosion to accretion occurred from 1977 to 1987.

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Punta Santiago, Humacao

Two main areas were defined based on net shoreline changes from 1962 to 1972. These were: Accretion occurred continually on the northern beach close to Boca Prieta and Rio Anton Ruiz. Sand accumulation was apparently related to river sediment sources that were transported by currents to the southeast. Low to moderate erosion rates were observed on the south beach. Erosion was caused by wave refraction patterns and human activities. As at Rio Blanco beach, waves approached from the east with a period of five seconds causing high energy concentration on the north side of the beach, producing a southward longshore current flow. However, this longshore current was partially blocked by a dock and groin structures, causing loss of sand to the beach budget.

No shoreline change data were available after 1972. However, based on field observations, the south beach still eroded and some beach segments completely disappeared. Erosion was caused by storm waves from Hurricane Frederik (1979) and Hugo (1989) that caused significant damages to the beach. Bush, et al., 1995 Also, the construction of a series of walls on the south beach blocked the possible gain of sand. A sand replenishment program was conducted on the south stations, but was not effective because the beach was filled with sand of the wrong grain size.

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Rio Blanco, Naguabo

Rio Blanco beach had low erosion rates from 1964 to 1987, except at stations 1 to 3 where accretion occurred. Most stations accreted in the period from 1964 to 1972, except for stations 2 to 5 and 7 where erosion occurred. High to moderate erosion was noted on the north stations located near the RÌo Blanco. A shift from accretion to severe erosion occurred on the south beach and a shift from erosion to accretion occurred on the north stations from 1972 to 1979. According to wave refraction plots, the south beach received higher wave energy than the north beach, when the waves came from the southeast, where high wave energy occurred. Erosion was related to the decrease in sediment river discharge and an increase of high amplitude waves.

Stations 7 to 17 on the south showed moderate erosion rates from 1979 to 1987. A decrease in erosion rates was caused by the emplacement of a riprap structure and sand fill. Stations 1 to 5 and from 18 and 22 had accretion for the same period.

A transitional terrigenous beach was measured for most of the stations at Rio Blanco. A reflective stage was present at station 1 which was close to the RÌo Blanco mouth. A steep beach face slope was observed on most of the profiles except during March, when a transitional stage was present.

A highly dissipative stage was observed at stations 2 and 3 located north of the rip-rap. According to wave refraction data, waves approached from the southeast with a period of 5 seconds and from the northeast with a period of 8 seconds, causing high energy concentration south of these stations and thus developing a longshore transport to the north which was blocked by the riprap. This caused a loss of sand for stations 2 and 3. Short period waves approaching from the east and northeast produced uniform low wave energy to the shoreline causing no significant development of longshore cells to cause loss of sand from the north stations. A stable transitional stage occurred on station 4 on the south side of the riprap. No significant changes occurred for this profile because the beach was stabilized by the riprap. Fine sand was found in the swash zone on these stations and mud was in the nearshore area. Therefore, no sand could be supplied from nearshore sources.

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