Development of a GIS-based Model for River Water Temperature Interpolation

Abstract

River water temperature is an important ecological measure and a complex phenomenon. A significant number of influencing factors with different levels of impact on the water temperature profile, and dynamic water temperature behaviour of rivers, must be considered. Critical factors represent air temperature, shade caused by riparian vegetation, flow velocity and solar radiation. In order to obtain exact water temperature values, on-site measurements have to be performed, however, it is not possible to equip every segment of the river with measuring stations. Therefore, the main goal of this project is the development of a GIS-based water temperature interpolation model that estimates the water temperature in rivers. Essential for this GIS-based model is the detailed definition of influencing factors and its spatial representation for developing an analysis model.In a first step, the target river network is segmented based on its tributaries. Segment points are set where tributaries join the major river, and therefore cause a mixing due to different water temperatures. Every segment with the calculated values regarding hydrology, geometry, meteorology, as well as shade, serves as an input for the applied water temperature interpolation tool "Stream Segment Temperature Model" (SSTEMP). This tool is used to calculate and interpolate the monthly average water temperature for every river segment. Following this procedure, pinpoint water temperatures are calculated for every river segment that can be exported to ArcGIS. Python Scripts support a semi-automated workflow to transfer all relevant geodata to the corresponding river segment where they are stored as attributes. Finally, the result can be visualized and highlighted, which enables the user to obtain modelled pinpoint water temperature information.