In this work we show the results of analysis of propagation of sound waves applied for an alert system in the river Chili, in Arequipa city. We used mathematical models, ISO standards, geographical, demographical and environmental variables of Arequipa. A complete mathematical model has been implemented in Matlab. It was compared with results generated by several commercial software, showing good coherence. As result of this paper, we propose a new methodology for the design of a network of emergency speakers for alert systems, assuring coverage and reliability.