Author(s): Deonie Allen; Scott Arthur; Heather Haynes; S. G. Wallis; N. Wallerstein
Linked Author(s): Stephen Wallis
Keywords: Debris transport; Prediction; Urban flood risk; Blockage; Solute dye tracing
Abstract: Debris movement and deposition resulting in culvert blockage, infrastructure damage and increased flooding is a known cause and effect in hydraulic analysis. The prediction of urban and small watercourse debris movement, both quantity and risk, has undergone only limited analysis predominantly due to lack of field data. This paper describes proof-of-concept field work enabling collection of accurate and meaningfull debris residency and transportation data from small watercourses. Passive integrated transponder (PIT) technology provides a method to collect debris transport field data within the urban environment. To date, debris transport analysis has focused on regional fluvial systems and large woody debris, both in flume and field experiments. Given the social and ecomonic risk assocated with urban flooding, and as urban drainage design shifts away from subsurface piped network reliance, there is an increasing need to understand debris movement in urban watercourses. The present paper examines the limitations and effective function of PIT tag technology to collect debris transport data in the field appropriate for risk and prediction analysis. PIT tags can withstand extended field exposure to provide meaningful field datasets. In this study, the tags are installed within artificial debris and released at known locations into a small urban natural watercourse; this is to allow monitoring of movement and travel time. Debris velocity and detention are collated with solute time of travel, watercourse and point flow charateristics to identify the relationships between these key variables. A static antenna provides pinchpoint recording of debris movement (frequency) that is related to debris size and entrainment location. Solute time of travel provides location specific calibration of stream flow and mixing. The work presented tests three hypotheses: firstly, that the potential for unobstructed or un-detained debris flow increases with velocity and water level. Secondly, that decreased travel distance and resistance forces, and increased solute peak concentration velocity, result in increased debris transport potential. And thirdly, the relationship between debris and channel dimensions is examined with the aim of advancing representative debris transport prediction modelling.