The module calculates crevasse splay morphology and water discharge outflow of a crevasse splay. The module is designed to calculate morphological changes and water discharge outflow of a crevasse splay that is triggered by a preset flood event and evolves afterwards. The inputs for "mainCS.m" should be daily water discharge and sediment flux series of the trunk channel upstream the crevasse splay. The outputs will be daily series for the cross-sectional parameters of the crevasse splay, and daily water discharge series of the trunk channel downstream the crevasse splay. One limitation of the present version is it only calculates the expanding and healing of a crevasse splay, while ignores the possible morphological change (demise or revival) of the trunk channel downstream the crevasse splay. Another limitation is the codes are originally written for the Lower Yellow River(a suspended load dominated river) for the purpose of calculating sediment budget in the Lower Yellow over a long timescale, say as long as hundreds years, so the present module can not be applied to other alluvial rivers without modifying those lines related to channel geometry, bankfull discharge and bank erosion(deposition).