When you cross the Arrow through its walkways you will see that there are certain inland dunes, like small hills stand on the general plain, regardless of the dune that leads to the beach.

The author of these undulations is Retama monosperma, a typical plant area casting deep roots in the soil, setting the ground. further, its peculiar form of bush with many branches helps retain airborne sand and accumulating it goes, while it is growing, to form from small ripples to real hills within the Arrow.

Source: Wikipedia