Effect of clogging inlet phenomenon on pluvial flood in urban areas

Abstract

This paper describes results of the 1D/2D coupled hydraulic model of the drainage system of La Almunia de Doña Godina (Zaragoza, Spain) with special focus on the surface drainage system formed by the grated inlets and their interaction with the sewer network. The software used for this analysis is Infoworks ICM (Autodesk). This software allows hydrological and hydraulic modelling in complex basins such as those with a high degree of urbanisation through the implementation of coupled or dual drainage models (1D/2D) and, relevant in this study, the hydraulic characterisation of the inlets. The main objective of the model is to evaluate the effect of partial occlusion of the grated inlets on the performance of the sewer networks and the surface flooding. For the model development, sewer topographic data have been used. For the surface drainage system, a comprehensive field work was conducted to locate, identify and characterize the grates and the different clogging patterns. From the data collected during the study and field work, 948 elements were found, characterized in 43 different typologies, digitized, introduced into the model and connected to the corresponding manholes of the sewer network. To simplify the analysis, the 43 types of grated inlets were grouped into 7 categories based on their geometry and size. Some clogging patterns were obtained from field observation and, in other cases, some of them were estimated considering an increasing trend of clogging. The hydrological model adopted was a hybrid one, considering a semi-distributed approach for the micro-catchments represented by buildings and internal courtyards (areas normally directly connected to the sewer network) and a distributed approach for the whole 2D domain (streets, squares, sidewalks, etc.) with generation of the flow rates directly on the cells (“rain on grid”). The polygons of the buildings and internal courtyards were treated as voids in the two-dimensional simulation domain on which an unstructured mesh was generated on a digital terrain model (DTM) with a resolution of 2x2 m. The analysis of the effect of inlets clogging on the hydraulic behaviour of the network and on surface flooding was carried out for 4 rainfall events (hyetogram corresponding to a 2-year return period and 3 rainfall events with a duration of 20 minutes and precipitation intensity of 25.26 mm/h, 20 mm/h and 10 mm/h). The results have been expressed in terms of total volume intercepted by the inlets, flooded areas on the 2D domain and hydrographs of the flow captured by inlets.

Postprint (published version)