# The Influence of Hard Protection Structures on Shoreline Evolution in Riohacha, Colombia
## 2 Study Area and Geographical Data  
The Colombian Caribbean coastline spans from the eastern border with Venezuela to the western border with Panama, primarily oriented in a NE-SW direction, with occasional segments aligning W-E (Figure 1). La Guajira peninsula is a complex region, where different Quaternary interactions (i.e., climate conditions, human intervention, tectonics) have defined the current geomorphology [32]. The entire area is a set of Jurassic to Tertiary tectonically uplifted blocks of granitic, metamorphic, and sedimentary rocks adjacent to sedimentary basins filled with Tertiary sediments [33]. Therefore, the landscape units include mountainous areas and extensive deltaic plains. The coastal morphology of the Peninsula, shaped mainly by marine conditions and coastal processes typical of tropical climates, is characterized by numerous bars and medium sandy beaches along elongated coastal plains, bays, and cliffs [33; 34]. In the Colombian Caribbean, tidal patterns are mixed semidiurnal and micromareal, with average amplitudes around 0.3 m and peak values up to 0.65 m [35; 36]. The dominant swell, influenced by climatological factors, comes from the NE-SW direction from November to July, with wave heights reaching 4.5 to 5 m [37; 38]. In the remaining months, swell direction becomes more variable, shifting to a SW-NE orientation, with wave heights under 1.5 m. During specific meteorological conditions, southerly winds generate short-duration, high-frequency waves, which can lead to significant erosion. Sea level rise in the Colombian Caribbean (based on data from the Cartagena station south of Riohacha) has shown a slight oscillation from 1950 to 2015, with rates ranging from 5.5 mm/year [16; 38] to 5.9 mm/year [39]. Projections for sea level rise by 2050 (starting from 2020) estimate an increase of 24-26 cm under moderate (Representative Concentration Pathway--4.5) or no reduction scenarios (RCP 8.5) [40]. Historically, sediment influx in the region came from the Sinu and Rancheria rivers, but damming of these rivers in the 1990s and mid-2000s altered sediment transport [41], shifting the main source to wind-driven processes from the upper Guajira region, with occasional reversals during heavy precipitation [42]. The city of Riohacha, located in the central part of La Guajira Department, has 46 km of coastline, approximately 7% of the Department [37]. The city, home to over 250,000 residents, relies primarily on tourism as its main economic activity. Previous studies have documented a long-standing pattern of beach erosion in the northern sector of the city, particularly near the mouth of the Rancheria River [37; 43]. To mitigate these effects, six groins were built at the end of 2007 along the 1.5 km waterfront of Riohacha city (Figure 2A). These groins measure 150 m in length, 13 m in width, and stand 6 m high, spaced at an average interval of 250 m [15]. Additionally, a seawall was constructed (Figure 2B). The Riohacha area is underlain by the Mongui Formation [44], composed of Paleogene and Neogene sandy claystones and semi-consolidated conglomerates with igneous pebbles [45]. This formation outcrops near the Rancheria River mouth but is covered southward by Quaternary sediments, mainly alluvial deposits from perennial rivers and streams. In the central and southern part of the city (Figure 2B,C), small beach deposits overlap these alluvial sediments, consisting of semi-consolidated sandy clays and plastic clays rich in ferromagnesian minerals and oxides from the Sierra Nevada de Santa Marta [46; 47]. Finally, the study focuses on a 5 km stretch of coastline between the mouth of the Rancheria River (north) and the indigenous reservation Las Delicias (south) (Figure 1). The area is divided into three sections (Figure 2):  
* Zone 1 (1450 m) extends from the river mouth to groin 6, encompassing the groin field and featuring well-developed beaches. * Zone 2 (1900 m) stretches from groin 6 to the Nuevo Faro neighborhood.