Alluvial is a dual-channel interactive installation commissioned for a private home. Two overhead video cameras track people’s movements in the entryway below while Utterback’s software outputs two dynamic animations to the projection screens. A person’s body adds visual information to one screen, while subtracting from the other, and this interplay of positive and negative, additive and subtractive qualities builds as more and more people enter the space. This process of simultaneous accumulation and disintegration creates a temporary beauty, where the buildup of delicate grains of sand (or points of light), can easily be disturbed by the bolder graphics indicating another person’s presence in the space.