COMPREHENSIVE ANALYSIS OF HYDROLOGIC PROCESSES AND NITRATE CONCENTRATIONS AT THE WATERSHED SCALE BASED ON CONTINUOUS MONITORING DATA

摘要

Mitigation of flood related damages and improvements to stream water quality require a thorough understanding of the relation between hydrologic processes and stream nutrient concentrations. Recent advances in technology allow for collection of high frequency data that can shed light on the interactions between surface water, groundwater, and water quality. In this study we analyzed nutrient concentrations, precipitation, soil water content, discharge, and groundwater levels collected every 15 minutes in the Otter Creek (122 km~2) a watershed in the State of Iowa, USA. We focused on the timing of different processes that occur at the watershed scale, from the onset of precipitation and early soil moisture changes, to production of runoff that leads to subsequent peak discharge and nutrient concentration. We propose a methodology based on time series slope thresholds that has the potential to enhance flood preparedness in areas prone to flash floods. Stream nutrient concentration trends were correlated with land cover, subsurface drainage, and LIDAR data. Measured data are also being used to calibrate a physically-based watershed model and numerical results from this model are presented in a companion paper entitled "Quantitative assessment of flood damage reduction projects through physically-based watershed models".