Journal of Coastal Research SI 59 218-228 West Palm Beach, Florida 2011 Coastal Evolution, Sea Level, and Assessment of Intrinsic Uncertainty M.A. Losada † , A. Baquerizo † , M. Ortega-Sánchez † , and A. Ávila †‡ ABSTRACT LOSADA, M.A.; BAQUERIZO, A.; ORTEGA- SÁNCHEZ, M., and ÁVILA, A., 2011. Coastal Evolution, Sea Level, and Assessment of Intrinsic Uncertainty. In: Roberts, T.M., Rosati, J.D., and Wang, P. (eds.), Proceedings, Symposium to Honor Dr. Nicholas C. Kraus, Journal of Coastal Research, Special Issue, No. 59, pp. 218-228. West Palm Beach (Florida), ISSN 0749-0208. The climate variability, its implication in coastal processses and the uncertainty that it therefore introduces in the morphological evolution of the coast are addressed. Historical evidences in the Iberian Peninsula allow relating the occurrence of significant variations in sea level position during the Holocene and its effect on the morphology, to natural climate changes. It is still unknown the way that long term climate variability will affect sea level position and the severity of other meteorological agents, which is a source of uncertainty that adds to the stochastic nature of coastal long term proccesses. In a decadal scale, under the assumption that sea level and other parameters that describe the climatic forcing remain stationary, the methodology by Baquerizo and Losada (2008) is used to predict the impact of the construction of a reservoir in the delta of the river Guadalfeo (Spain) and to illustrate how to deal with the uncertainties of the prediction for management purposes. Among other results, it is found that the probability that the shore retreats more than 120 m at any location is about 0.95, which allow to conclude that the construction of the dam will have a severe impact. ADDITIONAL INDEX WORDS: Morphodynamic evolution, climate variability, long term proccesses, anthropogenic impact. INTRODUCTION A large population and the infrastructures required for their living and developing are located in coastal areas. In fact, presently, about 40% of the world’s population lives within 100 kilometers of the coast, and this value is expected to rise up to 75% by 2050 (Masselink and Hughes, 2003). This increase in the population implies an increase in the pressure on coastal ecosystems due to, among others, habitat conversion, land cover change or pollutant loads. Besides that, the coastal zone (especially low-elevated coastal areas) is largely vulnerable to sea-level rise and other coastal hazards such as storm surges. The maintenance of the coast requires a correct management based on sustainability principles that are also capable of dealing with the natural and human induced processes occurring in the littoral zone. Traditional engineering works focused on maintaining the coastline that retreats due to erosion using five main strategies (Dean and Dalrymple, 2001): (1) doing nothing, (2) managing the retreat, (3) holding the line, (4) moving seaward or (5) accommodating the new scenario. However, the increase in the occupation of coastal zones and the occurrence of extreme natural events during the last decades showed the necessity of a more general approach. Since the beginning of the ninety’s a large number of proposals for the management of the coast using an integrated approach were developed in an attempt to achieve sustainability: the so-called Integrated Coastal Zone (Cicin-Sain and Knecht, 1998). These approaches require proper modeling of the morphological changes as the result of a complex multi-scale non-linear dynamic process that involves waves, currents and sediment transport in interaction with the environment. This multi-scale variability makes the management of the coast a question that has to be faced globally in time and space, dealing with the uncertainty associated to the stochastic character of the climatic forcing (Baquerizo and Losada, 2008). For changes occurring over decadal scales, Baquerizo and Losada (2008) presented a methodology to predict the evolution of morphological features driven by climatological agents and the assessment of the associated intrinsic uncertainty. For the application of the methodology it is necessary to know the sea level position and the distribution functions of the main parameters that describe the meteorological forcing. In a longer term basis, the evolution of the sea level position, introduce an additional uncertainty in the prediction of the morphological behavior, an issue that is becoming important in ____________________ DOI: 10.2112/SI59-023.1 received 21 September 2009; accepted 31 May 2010. © Coastal Education & Research Foundation 2011 †Grupo de Dinámica de Flujos Ambientales Centro Andaluz de Medio Ambiente Universidad de Granada Avda. del Mediterráneo 18006 Granada, Spain mlosada@ugr.es www.cerf-jcr.org ‡Técnicas Reunidas S.A. Departamento de Puertos y Costas. C/ Rafael Calvo, 9 28010 Madrid, Spain