Estimation of infiltration and inflow due to precipitation in a sewage basin

Abstract

Extraneous flows to sewer networks can occur underground (infiltration) or in the routing of rainwater (inflow). Infiltration in these networks is often inevitable, leading to system overloads and causing overflows. The range of values suggested by the Brazilian standard for the infiltration coefficient is quite broad, which may result in the adoption of elevated or inaccurate values, leading to imprecise sizing and consequent expenses and problems that could be predicted or avoided. Sizing problems can lead to chronic operational issues. The application of methodologies for estimating infiltration and inflow due to precipitation (IDP) presents itself as an important tool in addressing these challenges. The objective of this work was to propose and test a methodology to estimate infiltration and IDP in a sewage basin in a coastal region (Florianópolis, Santa Catarina, Brazil). This methodology was developed based on the operational conditions available at the sanitation company. The aim was to use what was available, without costly acquisitions, and thus quantify these elements. For this, two distinct methodologies were applied: one for the quantification of the inflow and the other for the measurement of underground infiltration and determination of the infiltration coefficient. The results showed a directly proportional relationship between rainfall intensity and IDP value. The measured infiltration coefficients resulted in values higher than those adopted in the project. It is expected that this research will contribute to reducing network overload and improving local sanitation management.