Catchment Dispersion Mechanisms in an Urban Context

Thursday, 18 December 2014: 11:05 AM
Jorge A Gironas1,2, Alfonso Mejia3, Florian Rossel1,3, Andrea Rinaldo4,5 and Fabrice Rodriguez6, (1)Pontifical Catholic University of Chile, Santiago, Chile, (2)CEDEUS, Santiago, Chile, (3)Pennsylvania State University Main Campus, University Park, PA, United States, (4)EPFL Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland, (5)Universitá degli Studi di Padova, Dipartimento di Ingegneria Civile, Edile e Ambientale,, Padova, Italy, (6)IFSTTAR Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux, Géotechnique Eau et Risques / Hydrologie et Assainissement, Bouguenais Cedex, France
Dispersion mechanisms have been examined in-depth in natural catchments in previous studies. However, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. Thus, these features can modify the variance of the catchment’s travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. This model computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment (France) as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2-3 km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further studies with other catchments are needed to assess whether the latter is a general feature of urban drainage networks.