STREAM HEAT BUDGET MODELING WITH HFLUX TO PREDICT SYSTEM RESPONSE TO CHANGE

Deterministic models of fluvial systems are useful for improving understanding of hydrologic systems and for predicting future conditions. Process-based models of fluid flow and heat transport in streams can help inform watershed management practices; these models can be used to quantify spatial and temporal patterns of stream temperature and to predict system response to future change. In this study, a stream heat budget model called the HFLUX Stream Temperature Solver (HFLUX) was developed and validated using observed stream water temperature data for Meadowbrook Creek in Syracuse, NY. The longitudinal, transient stream temperature model is programmed in MATLAB and solves the equations for heat and fluid transport using a finite difference scheme. Input data for the model were collected from June 13 to June 18 2012 over a 500 m reach of Meadowbrook Creek, a first order stream in the city of Syracuse, NY. Stream temperature data were recorded every 20 m along the stream at 5-minute intervals using iButtons (model DS1922L, accuracy of ±0.5°C, resolution of 0.0625°C). Meteorological data were recorded at 5-minute intervals using an on-site weather station. Stream dimensions, bed temperatures, and type of bed sediments were also collected. A constant rate tracer injection of Rhodamine WT was used to quantify streamflow every 10 m. Stream temperatures fluctuated diurnally by 3-5 °C during the observation period. Spatially, the stream shows a cooling trend along the reach, decreasing by 0.1-0.6 °C. Air temperature and solar radiation control the temporal changes in stream temperature at this site, while a 20% increase in streamflow due to groundwater discharge along the reach is controlling the spatial temperature changes. Modeling fluvial systems with HFLUX can help inform watershed management practices, specifically how a system will respond to stressors. HFLUX can be used to predict the response of a system to changing conditions, such as the impact of changing meteorological conditions or shading of a stream. It can also be used to perform a sensitivity analysis to determine the factors that contribute most to changes in stream temperature in a watershed. This work adds a user-friendly heat budget tool to existing models and it will advance the current understanding of the physical processes controlling stream dynamics.