MODELING THE GROWTH OF A DELTA: MODERN VS ANCIENT

There are 5 key processes that must be addressed in order to understand and model the architectural growth and stratigraphic development of marine deltas. These include: (1) the discharge of fresh water to the coastal ocean, (2) the discharge of sediment across the delta plain (including channel switching), (3) the dispersion of river sediment by surface and subsurface plumes, (4) reworking of the seafloor and shoreline by waves (and tides) in both the alongshore and offshore direction, and (5) the modification of accommodation space by compaction, subsidence, isostasy, and sea level fluctuations. There are many minor processes that affect these major variables including the role of ground water and gas on affecting excess pore pressure, biological feedbacks, aeolian transport and in the arctic the impact of thermal erosion and sea ice effects. Global databases exist for the basic variables (tides, discharge, waves, sea level), with other variables estimated or modeled (isostasy, compaction, subsidence, alongshore and offshore transport, plume dynamics).

Many models predict lithology in the vertical and horizontal dimension, with relatively few models able to predict in the longitudinal dimension. Most models are based on mass balance studies of modern deltaic systems, but few of these systems are pristine. Tank or flume efforts will be needed to test the veracity of future models. Research efforts should concentrate on scaling algorithms across time, wherever increasingly complicated numerical models may provide insight into first order analytical solutions. The role of climate on controlling the development of deltas remains a hot topic for future investigations.