I don't want to alarm you. There is

I don't want to alarm you. There is still enough sand left in the world to satisfy most holidaymakers but in many parts of the world beaches are literally being washed away and have to be regularly replaced.
First, much of the sand for beaches comes from cliffs which crumble away as they are pounded by the waves. To protect them, sea walls are often erected. With cliffs no longer crumbling, the beaches are robbed of the material which would normally feed them.
Beaches are also supplied with sand and gravel by rivers which bring it down from the mountains and hills. In some places rivers are being dammed and reservoirs built to retain water. They trap more of the sediment so the rivers take less sand and gravel to the sea. This is happening in California, for example, and in Scotland. In Egypt the building of the Aswan Dam has trapped the Nile silt, so much less silt is being fed towards coastal areas. That has meant the delta is now eroding instead of growing as before.
Thirdly, to improve access to the beach many holiday resorts build a promenade along the sea front. Like some of the fortifications of cliff faces, this usually has a flat vertical surface off which the waves bounce. This helps wash the sand away down the beach and most of it is lost.