Monitoring river restoration using fiber optic temperature measurements in a modeling framework

Graduation date: 2010The Middle Fork of the John Day River (MFJD) in Northeastern Oregon contains important spawning grounds for spring Chinook and summer steelhead of the Columbia River Basin. In the summer of 2008 phase one of a river restoration project was completed which included the addition of engineered log jams (ELJs) and scour pools. The restoration focuses on increasing habitat diversity and decreasing peak summer temperatures which, perhaps, had been degraded due to anthropogenic activities such as dredge mining, cattle grazing, channelization and deforestation.\ud This study utilized Distributed Temperature Sensing (DTS) technology to measure the temperature the MFJD study site before and after restoration during the summer of 2008. The temperature data along with other physical and climatic data were modeled using a physically based stream temperature model which incorporated groundwater inflows and an average depth of hyporheic exchange over the entire study reach. The root mean square errors for the pre- and post-restoration model are 0.57°C and 0.47°C, respectively. An average depth of the thermal mass associated with hyporheic exchange was calculated within the model to be 11m for pre-\ud restoration and 1.6m for post-restoration. It is unclear as to whether the hyporheic exchange increased due to restoration or is an artifact of high flows during the pre-restoration period. A statistical analysis was completed on the longitudinal temperature profiles of the MFJD to identify lengths of the river whose temperatures are different upstream and downstream. Groundwater inflow was defined as locations with cooler day time and night time temperatures than the surroundings whereas hyporheic discharge was defined as locations with cooler day time temperatures but warmer night time temperature than the surroundings. Statistically significant locations were highlighted for both pre- and post-restoration and equated to an average decrease in local temperature of 0.08°C pre-restoration and 1.18°C post-restoration. This equates to 0.004 m³/s and 0.012 m³/s of groundwater inflow for pre- and post-restoration, respectively. Again, these differences could be artifacts of high flows during pre-restoration and cannot conclusively be linked to the restoration efforts. However, the largest groundwater inflow (0.004 m³/s) can be associated with one ELJ structure and its corresponding scour pool