- Erosion risk levels at the NW Portuguese coast: The Douro mouth - Cape Mondego stretch - 43 Journal of Coastal Conservation 10: 43-52, 2004 © EUCC; Opulus Press Uppsala. Abstract. The entire northwestern coast of Portugal is under- going severe erosion and there are several areas at high risk of erosion. Commonly considered as a problem – because it jeopardizes human development along the coast – erosion is indeed a natural process of sediment redistribution. This paper presents a brief analysis of erosion driving forces and the subsequent state of vulnerability that coastal segments be- tween the mouth of the River Douro and Cape Mondego are facing. The paper also discusses erosion risk levels, low or high, and the subsequent questions whether there are popula- tions, economical assets or natural habitats at risk and/or areas prone to coastal flooding. Main challenges and future trends along the study area are identified in the light of understanding the underlying causes of conflicts and what realistically can be achieved given the morphodynamics and hydrodynamic proc- esses, human development established along this coastal seg- ment and the existing policies. Keywords: Erosion, Hydrodynamics; Littoral drift; Morpho- dynamics; Risk analysis; Shoreline development. Abbreviations: ICZM = Integrated Coastal Zone Manage- ment; POOC = Plano de Ordenamento da Orla Costeira (Coastal Zone Management Plan). Erosion risk levels at the NW Portuguese coast: The Douro mouth - Cape Mondego stretch Veloso-Gomes, F. 1* ; Taveira-Pinto, F. 1,2 ; das Neves, Luciana 1,3 ; Pais Barbosa, Joaquim 1,4 & Coelho, Carlos 5 1 Faculty of Engineering, University of Porto, Rua do Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal; 2 E-mail fpinto@fe.up.pt; 3 E-mail lpneves@fe.up.pt; 4 E-mail jlpb@fe.up.pt; 5 University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal; E-mail ccoelho@civil.ua.pt; * Corresponding author; vgomes@fe.up.pt General characterization The coastal area described in this paper is located on the Portuguese Northwest coast, facing the North Atlan- tic Ocean. This area is limited to the North by the mouth of the Douro and to the South by Cape Mondego (Fig. 1). It has a linear extension of ca. 110 km and a general orientation NNE-SSE. Coastal scenery includes two important environ- mental features: the lagoon of Aveiro, classified as a special protection zone by the Birds and Habitats Direc- tive, and a small residual lagoon, the Barrinha de Esmoriz. The dune system of São Jacinto situated in this area is a Natural Reserve as classified by Portuguese Law. From a geomorphologic point of view, this segment is mostly a sandy and low lying coast composed of alluvium sands and dune systems. Coastal morphodynamics is mainly shaped through wave action. Waves are indeed the dominant force, driv- ing the littoral processes on this coast. Although the wave climate changes seasonally, it can be characterized by medium significant wave heights from 2 to 3 m, with periods ranging from 8 to 12 seconds (Anon. 1993, 2003). Seasonal storms, particularly between October and March can produce significant storm surges when they coincide with astronomical tides. Waves can reach heights of more than 8 m, with periods reaching 16 to 18 seconds (Anon. 1993, 2003). The tide amplitude from low to high water can range between 2 and 4 m at spring tides, twice a day due to the semidiurnal characteristics of the tide. Furthermore, local wave phenomena, espe- cially refraction, diffraction, shoaling and also the bathymetry can influence tremendously local wave con- ditions. More detailed information on the characteristics of the wave regime in the area in analysis can be found in Pires Silva (1988) where also additional references can be found. Meteorological tides have little influence on water levels outside semi-enclosed, protected water bodies,