3.4.1. Beach and Dunes

According to Doody [48], a beach that is extending offshore due to accretion needs sediment. As the amount of sediment increases and the sediment balance of the beach moves from neutral to positive, large dune areas will develop, causing regenerative trends in the terrestrial ecosystems. In the study area, the coastline and the vegetation bordering it have been altered. The aerial photographs in the analysis of Psuty et al. [15], in the 1980s, show mobile coastal dunes moving across the headland, supplying the beach with sand. However, by the mid-1990s, vegetation had covered these mobile dunes. This trend has continued, and, with less sand available, sediment transport to the south has decreased. In addition, as the use of 90 ha of the mobile sand dunes has changed, only 10% of the original area of mobile dunes is now in its previous, natural state.

Regarding the morphology of the inlet, there is a southward sediment transport. As sediment is now scarce, the berm is less developed, which means that the inlet stays open for longer. This causes the tidal exchanges to sequester sediment in the northern part of the lagoon, increasing the area of the delta, inducing subsidence and deepening the northern part of the lagoon [15].

**Figure 11.** Land use and vegetation in La Mancha. Data from INEGI [47].
