Quantifying Coastline Change - Playa Guiones & Playa Pelada, Costa Rica

Abstract

<p>This study was conducted over two years (2005 and 2007) and consisted of data collected over one wet season and one dry season at two beaches, separated by a rocky headland, located along the Pacific coast of the Nicoya Peninsula, Costa Rica. Although the beaches are concurrent along a 7 km stretch of coastline, both are characterized by a unique combination of: beach slope, length and shape; sediment composition, size and mineralogy; and vegetation. These beaches have discrete land uses. Playa Guiones is a tourist beach that is experiencing rapid development and Playa Pelada is the only local beach that provides boat access for local fishermen. It was hypothesized that the active tectonism in the region combined with the distinct wet/dry seasons will result in dynamic beaches with distinct morphology. <br /> The first objective is to quantify and explain changes in sediment accretion or deposition between the two distinct seasons. The second objective is to quantify longer term temporal coastline changes through analysis of air photos and satellite imagery from 1940 to 2005 for the region. It was hypothesized that this time series will provide evidence of the influence of tectonics on coastline position. <br /> This analysis involves a comparison of Digital Elevation Models (DEMs) created from real-time kinematic GPS data collected in June 2005 and January/February 2007 with aerial photography and satellite imagery representing the period 1940-2005. Results show that from wet to dry season there is substantial net sediment accumulation for Playa Guiones and net sediment erosion for Playa Pelada. It should be noted that the seasons were particularly dry and particularly wet, thus, the results may indicate maximum levels of variation. The time series analyses of the digital imagery show little variation of coastline position during the period of record. The digital imagery was severely limited by the resolution and scale of the imagery. It appears that these beaches experience moderate to large amount of seasonal variation but are relatively stable over a longer time period.</p>