Examining the Effects of Geomorphology on Hydrologic Transit Times Using Liquid Water Isotopes

In recent years there has been resurgence in improving physically based and spatially distributed hydrological response models. However there continues to be many obstacles in accurately representing the basic processes governing rainfall runoff responses. Much of these inaccuracies can be attributed to such problems as a lack of understanding in runoff processes, unknown heterogeneity both at the surface and subsurface, variations in driving forces and the effects of geomorphology on the transformation of rainfall to stream flow. We hope to improve on such ambiguity is by examining the relationships between geomorphology and hydrology through the investigation of transit time distributions, which can be used as a fundamental descriptor of catchments" characteristics such as storage and flow pathways. By examining stable isotopic variability in precipitation, soil moisture and stream flow to determine transit times, we hope to better understand the effects of topographic land structures on the hydrologic response system. The first step in this process has been to fully instrument a series of hill slopes with similar structural and pedologic characteristics, located in the Marshall Gulch region of the Santa Catalina Mountains. Equipment including suction and non- suction lysimeters, tipping bucket rain gauges and automatic flow samplers with data loggers positioned to take stream flow and precipitation samples have been used to collect samples throughout the region. A description of preliminary results will be presented.