Materials ranging from wet tailings in retention ponds through potenti
ally acid sulfate sediments in humid marine environments to clay soild
s in semi-arid climates shrink and swell with change in water content.
This paper discusses the formulation and determination of material ba
lance in such swelling and cracking materials. Significant errors and
their likely magnitudes are identified when these estimates are based
in physical space, as opposed to material space. Ways in which this pr
oblem might be dealt with are discussed.