Water temperature of urban streams - climate change adaptation

Urban streams climate change adaptation

Müller Helene, Kleiner Jürgen, Philipp Stern, Rauch Hans Peter

 

Urban water courses are a system under pressure. Either they have been modified in the past, banned in the underground or even inundated in the sewage system. Within the north western part of the city of Vienna (research area: city of Vienna in the north of Wien river + in the west of Donaukanal) the runoff of a riparian catchment area of 20.8 km² arrives at the waste water treatment plant.  The ecological pressure, heavily modified water bodies are bothered with, is intensified by climate change. Despite these circumstances, the urban water courses should provide flood security as well as low flow security. In order to derive resilient systems restoration is essential. Within an urban context the spectrum reaches from water quality improvements, morphological restoration to reactivation of water courses in the underground or in the sewage system. The list of benefits is long, it covers the generation of urban blue green infrastructure (BGI), which can help with urban heat island (UIH) mitigation and leads to additional recreational areas, the availability of an additional water source in the urban area and many other ecosystem services. Regarding climate change and low flow situations the thermal regime of rivers is addressed. To restrict the warming of the water temperature shading via vegetation is an important factor. Within the research project ProBach a testfield of three artificial and temporal limited waterbodies (two running waters one stagnant waterbody) was installed in spring 2024 at an asphalted spot at the Klimabiennale in Vienna. In the context of installing BGI elements via urban river reactivation for UHI mitigation microclimatic, social, technical and river ecology related questions have been addressed. Regarding the latter, physio-chemical and biological water quality parameters were observed. The focus of the work presented in the poster is water temperature as a major factor for cooling the effects of water bodies. The interrelationship between water body, its riparian vegetation and the associated shading effects were observed.  The water temperature was monitored in a testbed, 7.8 m long and 80 cm broad, and a discharge of 1 l/s within a circular system. Natural riparian vegetation was simulated by shading nets with UV permeability of 60%. The water temperature was recorded by nine HOBO sensors at different positions of the riverbed (on the sediment, in the sediment, in the sump), air temperature was collected by eight TOMST sensors in 1.5 m height. During a heat period in July 2024 shaded and unshaded measuring campaigns were carried out repeatedly. The artificial shading of the water bodies impacts the water temperature significantly. The findings highlight the importance of riparian vegetation while restoring and reactivating water courses within an urban context in order to generate resilient, vital and climate change resistant river systems.