Oregon DEQ Watershed Management Section
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
Water quality management -- Oregon, Riparian areas -- Oregon -- Management, Solar radiation, Water temperature -- Oregon -- Coquille River -- Case studies
Warming stream temperatures degrade water quality by stressing cold-water species, promoting harmful algal blooms, lowering dissolved oxygen, and increasing the toxicity of some compounds. The influence of stream temperature on the survival of native salmon is of particular concern in the Pacific Northwest. Effective shade, the fraction of solar radiation blocked from reaching a stream, is directly related to in-stream temperature and can be manipulated by riparian management actions. Mechanistic models of effective shade are prohibitively data and cost intensive. The objective of this research was to develop an empirical model (Simple Shade) for evaluating effective shade across the state of Oregon over time on a consistent and cost effective basis. Model inputs included Normalized Difference Vegetation Index (NDVI) values derived from high-resolution aerial imagery, watershed area, topographic shading, and channel characteristics derived from digital elevation models (DEMs) and a training dataset of effective shade output from the process-based shade model Heat Source. The study area was the Middle Fork Coquille River, Oregon, and imagery data was collected in summer 2009. Principal components analysis and random forest models were used to analyze variable importance and predict effective shade. The Simple Shade model explained 45% of variation in effective shade and had a mean of squared residuals of 2.7% of effective shade units. The most important predictor variables were watershed area, mean NDVI and topographic shade angle to the South. This research demonstrated that an empirical model of effective shade has the potential to match the performance of a mechanistic model of effective shade. The correlation between shade and mean NDVI also suggested that NDVI could be a surrogate measure of effective shade. However, variability in imagery and longitudinal watershed characteristics likely obscured the relationship between NDVI and effective shade. An improved technique for normalizing image and longitudinal variability within a watershed is needed to implement Simple Shade as a tool for assessing riparian conditions across Oregon and elsewhere.
Costello, Erin, "Development of an Effective Shade Model for Water Quality Management in Oregon" (2018). Environmental Science and Management Professional Master's Project Reports. 39.