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ANALYSIS OF THE HYDRAULIC EFFICIENCY OF STORM WATER INLETS MOSTLY USED IN ARGENTINA

Congress: 2008
Author(s): Claudio Fattor, Héctor Barrionuevo, Jorge Bacchiega, Alejandro Secchi, Rosana Mazzon
Fattor Claudio: Hydraulic engineer, National Institute of Water, with main activity in the field of Hydraulic Structures and physical modeling. Barrionuevo Daniel: Hydraulic engineer, National Institute of Water, with main activity in the field of Hydr

Keyword(s): urban drainage, storm water inlets, hydraulic efficiency
AbstractIn many of the main cities of Argentina almost a unique type of storm water inlet has been used until principles of this decade, with a technical design of early 1940´s. As a result of the severe economic situation of the country around the year 2000, the characteristics of these structures turned very expensive its replacement or his application to new areas. This derived in the necessity to implement new and more efficient hydraulic designs, taking also into account the advantages that may provide the use of new materials and fabrication processes. These new designs were not always directed to maximize the hydraulic efficiency, but to guarantee good conditions of circulation for pedestrians and vehicles, to diminish the possibilities of damage by vandalism and to avoid their robbery, among other aspects. The purpose of this work is to present an analysis of the incidence of storm water inlets design on its hydraulic performance, considering additionally the incidence that obstructions like solid wastes can generate. To such aim, an experimental device was constructed in the Laboratory of Hydraulics of the National Institute of Water, allowing to analyze the hydraulic behavior of these structures at 1:1 length scale. The model includes an approximation flow area with their cross-sectional and longitudinal slopes, the zone of location of the storm water inlet, which can be positioned at the same level of the street or below that (depressed area), and the discharge flow measurement device that allows to know the intercepted flow by each part of the inlet. The work methodology consisted of testing different isolated storm water inlets of approximately 1.00 m-long by 0.50 m-wide for longitudinal street slopes of 0.1% and 0.5% and one cross-sectional slope of 2.0%, taking as an additional variable the possibility of positioning the inlet device in a depressed zone. The water depth at the upstream section of the inlet, the flow intercepted by the bottom grates, the flow intercepted by the lateral opening and the exceeding flow were determined for each flow discharge being circulated in the street. The influence of total or partial obstruction of the storm water inlet on the efficiency of the device as a consequence, for instance, of solid wastes or leaves was also analyzed. Besides that, the efficiency experimentally obtained was compared with other criteria, like that developed by Universidad Politécnica de Cataluña (UPC). The hydraulic efficiency was obtained by these tests, determining the incidence of longitudinal slopes as well as the lost of efficiency as a result of obstructions of the storm water inlet. In addition, the estimations of hydraulic efficiency carried out with some expressions like that presented by UPC have shown, for some designs, an important difference compared to the experimental results. These results allow seeing a noticeable incidence of the geometry of the grate, whose hydraulic performance must be precisely determined to know the efficiency of the storm water inlet to be installed as a fundamental part of urban drainage system.
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