A group of pebbles is commonly called a Pocket. Other collective nouns you may see include Desert and Superfluity.
A collective noun for pebbles is a "rivulet". Similar to a brook or stream, a rivulet refers to a small or narrow channel of pebbles found along riverbeds or near bodies of water. This collective noun aptly conveys the image of a collection of pebbles forming a path or following the course of a flowing water, creating a vivid picture of nature's beauty. A rivulet can also symbolize the continuous movement and timeless presence of pebbles, as they are eroded by water over time, transported along the stream, and eventually deposited at different locations, constantly reshaping the earth's landscape. Thus, a collective noun like "rivulet" appropriately captures the dynamic nature of pebbles collected by the elements of water and rearranged in captivating formations.
Known collective nouns for Pebbles include: