On-site drainage systems: performance evaluation of the control of surface runoff

Abstract

The process of occupation of urban areas produces significant impacts on the water balance of the cities. The introduction of large impervious surfaces result in considerable increase of the volume of surface runoff and occurrence of urban floods. In order to mitigate this problem, technical and scientific community are seeking solutions of drainage systems that provide a lower impact during the process of development and works to complement the traditional solutions of drainage systems. Thus, these drainage systems, called source drainage, consist of technical solutions based on retention and detention, operate in lots of built-up areas and should be designed to maintain or restore the water balance in the period before urban occupation. In this way, this system reduces the volume of stormwater collected by the drainage building system that is disposed in the conventional urban drainage. However, the lack of technical knowledge regarding the performance, operation and limitations of source drainage systems generate several questions regarding its application and efficiency in combating urban flooding. Despite the possible benefits of source drainage it is necessary to emphasize that this design of drainage systems is relatively new, many of these techniques are currently used inappropriately because of the lack of a technical data base to enable a correlation over local parameters and design criteria. Thus, the study of this theme is justified because of the need for further investigation and monitoring over the long term for the techniques and methodologies are fully consolidated. The objective of this study is to evaluate source drainage systems, implemented in an experimental area in order to identify variables involved in their performance based on the observation of its operation during real and simulated rain events. The evaluation of the efficiency of the systems will be done over a seasonal cycle, by monitoring of geotechnical and hydrological parameters and comparison of hydrographs and infiltration profile of typical systems characteristics. The experimental systems will be tested for artificial rains with controlled flow and actual events that occurred during the study period. During the tests will be monitored the following variables: (1) soil moisture, (2) pore pressure, (3) water level, (4) emptying time, (5) input flow and (6) infiltration rate. These variables will be monitored by equipments installed in the boundary region of the infiltration systems. These data will be organized according to their relevance to support the development of a doctoral thesis, which aims to develop a mathematical model to represent these systems when subjected to different conditions of design parameters, considering this type of soil. As a result it is expected to determine the operational performance of drainage systems studied, when subjected to different conditions of intensity and duration of precipitation and saturation of the soil. In addition, we intend to raise the main parameters needed for the design, operation and maintenance of the studied drainage systems, and also to classify the most relevant variables to the performance of these systems. Data that will support the future development of a numerical model for the representation of the studied systems. Finally, the results obtained in this research will contribute to improve knowledge about the technical design, technical feasibility and limitations of application of rainwater infiltration systems in lots of built-up areas. (AU)