studying coastal geomorphological changes on beaches located near of the Rio Grande de Manatí Watershed, Puerto Rico (1977-2015): and its management implications.

A study of beach geomorphology changes was conducted in beach systems located near to the river mouth of the Rio Grande de Manatí in the north-central coast of Puerto Rico Island (1977-2015). The main objective of this study was identify the role of river and land cover and land use changes (LCLUC) over changes in beach geomorphology. An integration of field work, remote sensing (historical aerial photos and multispectral images), Global Positioning Systems (GPS), Geographic Information Systems (GIS) and evaluation of published databanks (USGS water data, LCLUC) were used to generate and analyze data in this study. Results showed three different beach geomorphic systems along the study site. These are: 1) a wider terrigenous beach located westward to the river mouth; 2) a narrow mixed terrigenous and biogenic beach on the eastward site of the river mouth; and 3) a wide biogenic beach on the eastern site of the coastline. Historical shoreline changes showed that major loss of sand was observed along all beaches from 1995 to 1997 period (10 to 50 meters). Shift from accretion to erosion and vice versa were found in beach segments from 1971 to 1977, 1977-1985, 1985-1991, 1997-2003 and 2003-2010 periods, where major shoreline changes were identified mainly in the biogenic beach. LCLUC distribution showed a major reduction in agriculture land use (from 58% to 6%) from 1977 to 2010. This land was converted mainly to forest and rangeland during this period. Major flood events occurred in the study site from 1992 to 1995 may associated with major loss of sand on beaches in the study area. Detail association between shoreline changes and LCLUC/hydrological process will be defined during the second year of the project. This assessment is important to generate information to develop coastal management plans that helps community and ecosystems planners to be proactive during risk events in the area.