Metodología numérico-experimental para el análisis del riesgo asociado a la escorrentía pluvial en una red de calles

Resumen

Surface waters running in the streets are a common feature in cities which have a superficial storm drainage system as well as in cities that have not. The surface storm drainage system consists of open channels and the streets. In developed zones which have a sewer system, rainwater must go from the surfaces where it has fallen towards the inlets and this process often takes place over the street. In many cases, the slope of the streets can be steep enough to accelerate the flow to velocities or combinations of velocities and the depth can be risky for the users of the streets, both pedestrians and drivers. For the assessment of the risk associated to this flows it is necessary to know the maximum depths and velocities that we might expect in the streets for a specific return period and the maximum discharges that will take place in them. The main aim was the development of a numerical model to compute the flow characteristics (velocity, depth) in streets forming a network. The knowledge of the flow distribution in the crossing is the key question in the modelling of flow in the street network. The model must be able to simulate 1-D unsteady flow in the street network. A scale model of a street crossing has been built and a series of tests has been conducted for studying the flow pattern in the crossing when the flow in the streets is supercritical. In light of the experiments it has been found that the inflow power ratio can be used as a non-dimensional parameter for predicting flow distribution as well as the flow pattern. On the basis of those relationships a one-dimensional formulation can be developed in order to predict the dividing flow in crossings and networks of steep streets. A review of the existing criteria to evaluate the risk associated to the urban runoff on streets is made. Two new criteria based on theoretical analysis of the water's force acting on a static pedestrian are presented, no slipping criterion and stability to tilt criterion. According to these criteria, either a maximum depth, a maximum velocity or some relations between depths and velocities should be fulfilled in order to guarantee the pedestrian's and driver's security in the case of medium to hard storms. The proposed numerical model was used to solve the storm runoff in an urban watershed of the city of Mendoza (Argentina), which has streets steep enough to produce supercritical flows. The results are evaluated bearing in mind four risk's criteria. As a conclusion, the numerical model is shown to be a useful tool in relation to the application of the risk's criteria. As an example, urban runoff risk maps of the network street belonging to return periods of 5, 10 and 25 years are presented.