The Guadiana jetties (constructed in 1974) are situated at the southern border of Spain and Portugal at the Guadiana river mouth. After the jetties were constructed, the coastal stretch west of the river mouth experienced a continuous trend of accretion, while the down drift sectors were subjected to severe erosion. These jetties are source of environmental problems and create long term economic impacts in positive and negative ways to the surrounding coast-line. The purposes of this study are threefold; to provide an estimation of the volume of the sands accumulated in the updrift side, to estimate the economic impacts of the sand deficit in the Guadiana estuary, and to define a relationship between the cost of erosion and accretion. Borehole drilling was used to estimate the volume of accreted sand. The respective cartography was done with the help of ArcMap GIS. Subsequently the economic impacts due to the jetty construction were estimated by considering the sand nourishment cost. The results showed an average progradation area of the western estuary margin by 3.8×105 m2 since 1974, accumulating an estimated 6.2×105 m3 of sediments. Also, 4.6 million Euro touristic income is generated by the Portuguese and 12.2 million Euro touristic income is lost by the Spanish government due to erosion of the beach. However, the Portuguese side’s cost of accretion is higher than the Spanish side’s cost of erosion. The conclusion drawn is that the Portuguese side has gained more economic and social benefits, and conversely, the Spanish side has lost their economic income and land due to the jetty construction.