A METHODOLOGY FOR THE EVALUATION AND DESIGN OF IMPROVEMENTS IN WET WEATHER SANITARY SEWER SYSTEMS IN THE MUNICIPALITY OF LUQUILLO, PUERTO RICO: A PILOT CASE STUDY

This paper describes the methodology that has been used to evaluate wet weather flows within the sanitary sewer system in the municipality of Luquillo, Puerto Rico. The methodology is based on a unit hydrograph model that predicts rainfall dependent infiltration and inflow (RDI/I) for a given unit of rainfall (volume or intensity). The RDI/I model has been calibrated by comparing predicted wet weather flows to those observed in the five flowmeter locations for which rainfall and flow rate data has been collected. Once the RDI/I is calibrated to the data collected from these five locations, then the methodology may be used to extrapolate to other areas which exhibit similar RDI/I characteristics in terms of rainfall and sanitary sewer system infrastructure.An extensive flow monitoring program has been undertaken to quantify existing wet weather sanitary sewer system flow characteristics in the Luquillo study area. Five flow monitoring locations have been deployed in areas that were determined to provide appropriate coverage of geographical as well as water/land use conditions. Flow data, consisting of flow rate, velocity, depth and rainfall intensity, was collected over a period of 45 days in order to capture rainfall events which produced significant RDI/I response. This is the set of data which has been used as input to the hydrograph decomposition methodology presented here.Section 1 describes the basic sanitary sewer system flow components that are considered in this analysis, and the methodology used to decompose flow monitoring data into these components. Section 2 presents the specifics of the hydrograph decomposition methodology for data analysis which is used to predict RDI/I flows for a given rainfall event. Section 3 presents the results obtained from the data analysis. Finally, Section 4 discusses some preliminary guidelines to be used in planning and design of improvements to the Luquillo sewer system.