Abstract

Climate has historically been recognized as an influence on sediment flux and deposition. The North American Monsoon is suggested as the forcing mechanism of deltaic progradational events of the Rio Grande River delta. Interpretations of reflection seismic profiles reveal that eustatic rise in sea-level from the Last Glacial Maximum to present is accompanied by several regressional events of the Rio Grande delta 5.5, 9.5, and 11.5 ka BP. Much of the migration of depositional facies within a delta system is forced by hinterland tectonics and base-level rise and fall. However, we suggest that the movement of facies within the Rio Grande delta system represent climate forcing as the most dominant influence on sediment deposition during this short time period. While dominance of climate influence is possible, the sensitivity of an increase in monsoon precipitation and its effect on sediment flux has not yet been tested. We test monsoonal effects using relationships between sediment flux, river discharge, and precipitation. Heavy water management and withdrawal and complexity of precipitation timing and events within the region make the relationship between precipitation and sediment flux difficult to quantify using modern data sources. Therefore, it is necessary to numerically simulate stream discharge to test potential sensitivities of the system to monsoonal precipitation using a stream discharge model. Precipitation input into the stream discharge model is gathered from a suite of climate model simulation outputs. Suspended sediment flux is derived from the outputs of the flow models using empirically derived sediment rating curves. Results of sediment modeling show that increased precipitation during the monsoon months of July-September, 6 ka BP increased monthly suspended sediment flux by 79 percent. The suite of climate models does not include 9 or 11 ka BP, but we suggest the monsoon may have been stronger during this time based on greater received insolation at these times. This study also shows that duration and intensity of monsoonal precipitation events can more greatly affect stream discharge and sediment flux than increased precipitation with constant storm intensity.

Degree

College and Department

Physical and Mathematical Sciences; Geological Sciences

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