Oregon Department of Environmental Quality
Date of Award
Master of Environmental Management (MEM)
Environmental Science and Management
Riparian restoration -- Oregon -- Johnson Creek Watershed (Clackamas County and Multnomah County), Riparian areas -- Oregon -- Johnson Creek Watershed (Clackamas County and Multnomah County), Solar radiation
The influence of stream temperature on the survival and reproductive success of anadromous salmonid populations has become an increasingly concerning issue in the Pacific Northwest. Enhancing the height, density and extent of riparian vegetation is widely accepted as one of the most effective strategies for reducing stream temperatures, while also providing numerous ancillary benefits. Effective shade is defined as the percentage of direct beam solar radiation attenuated and scattered by riparian vegetation before reaching the stream surface and is a commonly used criterion for choosing where to restore riparian vegetation. This project aims to prioritize sites for riparian restoration through effective shade modeling within the geographic extent of the Johnson Creek watershed. Modeling inputs included a limited set of channel morphology and riparian vegetation attributes and were sampled from high spatial resolution LiDAR derived raster datasets (3 ft.) using Python script programming tools. A separate raster was created to depict restored conditions, in which the height of all restorable riparian vegetation is set equal to 27 meters. Using the stream temperature model, Heat Source, effective shade simulations were performed along the mainstem Johnson Creek and all tributary streams over the duration of a single day in August. Model outputs provided effective shade and daily solar flux attenuation estimates under current and restored conditions, the difference of which represented the net benefit, in terms of shade, that would result from restoration. Model outputs were used to evaluate the current level of effective shade in the watershed and to prioritize restoration efforts at the taxlot, subwatershed and jurisdictional scale. Currently, effective shade is 73% on average for all streams in watershed. Under a restoration scenario, 544.9 acres would be restored resulting in the additional solar flux reduction of 209,118.9 watts/m2/d. Restoring only 22% of all taxlots or 21% of all restorable acres would accomplish 50% of the cumulative solar flux reduction. Restoring 38% of all taxlots or 55% of all restorable acres would accomplish 90% of the cumulative solar flux reduction. Prioritizing at the taxlot scale, as opposed to subwatersheds or jurisdictions, promotes a higher level of efficiency in the prioritization of restoration efforts. All taxlots should be further screened prior to final prioritization for opportunistic prospects such as landowner willingness, community support or proximity to existing restoration projects, and fundraising opportunities.
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Sahatjian, Brittany, "Modeling Effective Shade to Prioritize Riparian Restoration Efforts in the Johnson Creek Watershed, OR" (2014). Environmental Science and Management Professional Master's Project Reports. 42.