Collaborative Research: Investigating Human and Climate Influences on Delta Evolution Using Fluvial Discharge and Coastal Evolution Models

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Influenced by both terrestrial and marine processes, deltas are critical sedimentary landforms at the land-sea interface that provide records of past environmental changes. Deltas worldwide are currently being severely altered by human activities, in particular river damming, which has reduced the amount of sediment reaching the coast. Although large dams are relatively recent phenomena, human alteration of landscapes has been ongoing since the advent and expansion of agriculture. Combining field data collection, fluvial modeling, and coastal evolution modeling, this research will examine whether human activities have significantly influenced the formation of the modern Ebro Delta, on the Mediterranean coast of Spain. Specifically, it is hypothersized that the growth of the Ebro Delta can be attributed to massive deforestation for agricultural purposes initiated in Roman times. Field research will document the evolution of the Ebro Delta over approximately the last 3,000 years by collecting and analyzing sediment cores from along the delta plain. The climate-driven hydrological model HydroTrend will be used to compute riverine sediment discharge to the coast over this time period, incorporating changes to sediment delivery that could be attributable to climatic changes and those that could be caused by human alterations to the Ebro River watershed. A numerical model of shoreline evolution capable of incorporating long timescales will be applied to examine the causes of the delta's shape and to evaluate how changes to riverine discharge would affect the coast after being reworked by waves. Coupling of the fluvial and coastal numerical models serves an important goal as proof-of-concept of the Community Surface Dynamics Modeling System (CSDMS).Understanding the historic and future morphologic change of deltas has become increasingly important as sea levels rise and sediment loads feeding deltas continue to be sequestered behind dams in the hinterland. Deltas are often densely populated and provide many importantt natural resources to society, particularly along the rocky Spanish Mediterranean coast with scant land near sea level. In regions that have been affected by human civilization, deltas can serve as a record of climate and land-use changes across large watersheds. The Ebro Delta, Spain, with its distinctive plan-view shape, has experienced significant morphologic changes over the last two millennia; changes that may be attributable to human activities in the Ebro watershed. The results of this research will have wide applicability to unraveling the history of deltas worldwide (e.g., Nile, Po, Danube, Indus, Mississippi). If human activities are largely responsible for the shape of the world's deltas, this would provide an important context for understanding how humankind will manage these resources over the coming centuries, particularly as climate changes and humans continue to alter these landforms.