GROUNDWATER ROUTING AS A CONTROL ON STREAM NETWORK DEVELOPMENT FOLLOWING CONTINENTAL GLACIATION

A key objective of the Intensively Managed Landscapes Critical Zone Observatory (IML-CZO) is to understand the development of Midwestern landscapes following the end of the Wisconsin glacial maximum, approximately 10,000 years ago, through the conversion to intensive agriculture. Immediately following deglaciation a significant fraction of the uplands of the IML CZO was unconnected to external drainage networks and seasonal wetlands occupied closed depressions. Over time, the undrained area was integrated into river networks like the Sangamon River of east-central Illinois. The process of network expansion was not complete when intensive agriculture was established and artificial surface and subsurface drainage systems were imposed. We numerically modeled the development of groundwater flow paths in conjunction with natural river network formation in order to assess the significance of groundwater flow in setting the pace of network growth and influencing the network structure of tributaries. Preliminary results show that groundwater flow patterns evolve with stream networks. The groundwater moving from the highlands is funneled into channel headwaters. As time progresses, the stream network propagates across the model domain, engulfing areas of internal drainage. We present simulations comparing stream networks developed with and without coupled groundwater systems to illustrate the potential impact of groundwater on network evolution. In future studies, we aim to couple the hydrologic model with a reactive transport model to understand how groundwater flow paths and weathering profiles evolve together.