Abstract: Computer Modeling of the Evolution of Fluvial Systems

VINING, MARK R.
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

This work presents a computer model of the long-term behavior of a river system coupled to the geomorphic and tectonic evolution of its drainage basin. Past investigations have been mostly qualitative and theoretical; however, simulation of the interaction of the many processes and factors affecting a watershed over time can only be accomplished by a quantitative computer model. Existing quantitative models, which are limited to short stream segments and the time spans of individual flood events, fail to account for the simultaneous evolution of all parts of the river system. The work discussed here is a forward dynamic simulation of sediment deposition and erosion, at a scale involving the composite effects of many seasons of floods, regional tectonic subsidence, and sea-level fluctuation.

The method involves modeling a river system by a series of cells representing stream reaches having relatively uniform flow and sediment properties. Water and sediment are supplied from a model of the geomorphic evolution of the drainage area. Sediment characteristics are represented independently for layers of alluvium, soil profiles, and underlying bedrock layers. Bedform type, distribution, and dimensions are modeled for determination of bed surface roughness. Soil development is modeled from decay of strata underlying the land surface. Vegetation biomass is modeled from temperature, rainfall, and surface erosion conditions.

The method keeps geomorphic causes and effects temporally and spatially correlated, enabling systematic investigation of the pattern of evolution of a river system. Results yield the history of stratigraphic development of the basin, including the distribution and properties of all sediments deriving from the interaction of basin physiography and fluvial processes. The fluvial evolution model can be linked to a quantitative dynamic sequence-stratigraphic model of a coastal area in order to shed light on stratigraphic consequences in both the fluvial and coastal sedimentary records.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas