Colombia (Fig. 1) is a country with 5548 km of coastline bordering the Caribbean Sea (2733 km) and Pacific Ocean (2815 km). Analysis of coastal evolution trends developed by Posada and Henao (2007) for the Pacific coastline and Rangel-Buitrago et al. (2015) for the Caribbean coast revealed that 23% of the Caribbean coastline and 49% of the Pacific coastline are experiencing severe erosion problems (Table 3). The spatial and temporal variability of coastal erosion in Colombia can be related to the heterogeneity of the coast and a diversity of factors contributing to erosion–accretion processes of differing intensity along the coastline. In general terms, the coastal erosion in Colombia seems to be strongly influenced by regional natural and human-induced processes, such as sea level rise, extreme events, sediment supply, anthropogenic induced sedimentary imbalances, and subsidence.
Pacific coastline study area
The Pacific coast of Colombia extends along the west of the Cordillera Occidental, between Punta Ardita and the Mira River Delta. Its general orientation is N–S, with some sectors oriented NE–SW. In this area the Nazca plate and the South American plate meet and therefore the Pacific coast of Colombia is an active tectonic zone with a record of high-magnitude earthquakes.
The geomorphology of the Pacific coast of Colombia comprises cliffs alternating with terrigenous sandy/shingle coves, wide sandy beaches and sandy–muddy tidal flats, barriers, barrier islands and segmented sand bars, and intertidal mudflats and mangrove swamps.
According to Correa and Morton (2010), the climate of the Pacific coastline is humid tropical, dominated by the annual migration of the Intertropical Convergence Zone (ITCZ) and by the high mountains of the Cordillera Occidental. Average annual temperatures are around 26 °C, with minimum values of 14 °C.
On the Colombian Pacific coast, high rainfall values have been recorded: the mean annual rainfall is 10 m. The high rainfall is the result of remarkable atmospheric convective activity highly influenced by latitudinal migration of the Intertropical Convergence Zone (ITCZ). The ITCZ distributes the rainfall bimodally in the northern zone, so there are two rainy seasons: from April to June, and from September to November. In the latter season, precipitation reaches values of 0.57 m/month. In the southern zone, rains have a unimodal distribution, with abundant rainfall from January to June and an average of 192 rainy days. Likewise, the occurrence of regional climatic processes such as El Niño and the Choco jet stream as well as local conditions (i.e. terrain and vegetation, latitude, altitude, and sea currents) can produce variations that disturb the response to the influence of the ITCZ.
Tides along the Pacific coast are mixed semi-diurnal, with mean amplitudes between 2 and 4 m. Spring tide amplitudes change slightly along the entire coast; they vary between 3 m at Tumaco to 4.5 m at Buenaventura city. Winds along the Pacific coastline blow from Baudó Range (s), and from the west to southwest along the central and southern sectors of the Pacific coast. Swell waves along the Pacific coast are about 0.5–1.5 m high during calm periods, but can be as high as 2.5–3.5 m during strong winds (Correa and Morton 2010).
The Pacific coastline remains mostly uninhabited and undeveloped. It is divided into four departments including 18 municipalities with 0.9 million inhabitants. This population (1.8% of Colombia), is mainly concentrated in two port cities: Buenaventura and Tumaco (DANE 2015).
Caribbean coastline study area
The Colombian Caribbean coast extends between the eastern frontier with Venezuela and the western frontier with Panama (Fig. 1). The general coastal orientation is NE–SW, with some sectors oriented W–E, so that long linear segments alternate with bays. This coastline is a complex region, where tectonic processes have defined the actual topography and the landscape units include mountainous areas and extensive deltaic plains (Correa and Morton 2010; Rangel-Buitrago et al. 2013). Quaternary interactions among tropical climate, oceanographic processes, and tectonic activity have produced a varied unstable littoral geomorphology characterized by bars and beaches along the flat coastal plains, spits, and cliffs (Martínez et al. 2010).
Precipitation is seasonal, with two rain periods (April–May and October–November) and two dry periods (November–April and July–September). Maximum annual precipitation is approximately 2500 mm, while mean annual temperatures of <28 °C make the area attractive for the development of tourism (Rangel-Buitrago et al. 2013).
Tides are mixed semi-diurnal, with maximum amplitudes of 65 cm (Andrade 2008). Coastal dynamics are influenced by how the intensity and seasonality of the trade winds affect wave propagation in the shallow waters, and by rising sea level (Restrepo et al. 2012). The average significant wave height is 1.5 m; peak period average is 7 s. From November to July the wave system is dominated by NE swells; for the remainder of the time, waves are from the NW, WSW and even SW. This seasonal variation in wave direction corresponds with a decrease in significant wave height, with the lowest values occurring between August and October (≤1.5 m); whereas the highest energy conditions occur from November to July, when wave heights can exceed 2 m (INVEMAR 2006; Restrepo et al. 2012). Longshore sand drift has a dominant south-westward component, but minor reversals to the northeast occur during rain periods when southerly winds become dominant in some sectors and set up short, high-frequency waves able to cause significant shore erosion along cliffed and mud coastlines (Correa and Morton 2011).
The Caribbean coastline is a developing region, divided into eight departments and including 28 municipalities with over 4 million inhabitants. This population (8.5% of Colombia), is mainly concentrated in four commercial and tourist cities: Barranquilla, Cartagena de Indias, Santa Marta, and Riohacha (DANE 2015).