  We present a new approach to coarse-graining of variables describing dust
flow in GR. It is based on assigning quasi-local shear, twist and expansion to
2-dimensional surfaces with the help of isometric embeddings into the
3-dimensional Euclidean space and deriving the time evolution equations for
them. In contrast to the popular Buchert's scheme it allows to coarse-grain
tensorial quantities in a coordinate-independent way. The framework can be used
to estimate backreaction in inhomogeneous cosmological models.
