How does the damming of large rivers cause beach erosion?

River don't just carry water from its catchment to oceans they also carry a large amount of sediments which gets deposited at their delta. Carrying capacity of sediments varies with speed. Standing water has very little capacity to carry sediments. read more

Now on beach. Coastal areas constantly gets eroded by waves but gets deposition by river or wind resulting in a more or less balanced situation. When we decrease sediment deposition capacity of river by building a dam, net effect of waves and river deposition results in erosion. read more

Large reservoirs and dams without low level outlets will typically trap more than 90 per cent, and sometimes almost 100 per cent, of incoming sediment. Clear water below a dam is said to be 'hungry': it will seek to recapture its sediment load by eroding the bed and banks of the river. read more

There is no erosion on the Moon. All that happens is sudden changes on the surface, when meteorites pelt it. Other than that, nothing changes. read more