GRAIN2 - PREDICTIONS OF PARTICLE-SIZE SEAWARD OF RIVER MOUTHS

An ANSI standard FORTRAN-77 numerical model is provided. The model pre dicts the spatial and temporal change in seafloor particle size seawar d of a river mouth. The model needs the input files generated by a sis ter program DELTA2, a 2-D model that simulates the progradation of a r iver delta and the resultant fill of one or more marine basins. GRAIN2 tracks four size fractions in the mud-size range: coarse silt, medium silt, fine silt, and clay. Their spatial distribution is determined u sing (1) a velocity distribution developed from a buoyancy-dominated, free, 2-D jet flowing into a highly stratified marine basin; and (2) a particle-scavenging model that takes into account the biogeochemical affects of settling of particles in a marine environment (i.e. floccul ation). This hemipelagic component is predicted seasonally (four times a year) based on fluctuations in river velocity and river mouth shape , and on the suspended load discharged into the sea. Sand deposition i s predicted from the seasonal rate of turbidity current deposition, an d from DELTA2. The model is sensitive to changes in river mouth positi on and thus sediment supply and sea level fluctuations.