Assessing dry weather ow contribution in TSS and COD storm events loads in combined sewer systems

摘要

Continuous high resolution long term turbidity measurements along with continuous dischargenmeasurements are now recognised as an appropriate technique for the estimation of in sewer totalnsuspended solids (TSS) and Chemical Oxygen Demand (COD) loads during storm events. In thencombined system of the Ecully urban catchment (Lyon, France), this technique is implemented sincen2003, with more than 200 storm events monitored. This paper presents a method for the estimationnof the dry weather (DW) contribution to measured total TSS and COD event loads with specialnattention devoted to uncertainties assessment. The method accounts for the dynamics of bothndischarge and turbidity time series at two minutes time step. The study is based on 180 DW daysnmonitored in 2007–2008. Three distinct classes of DW days were evidenced. Variability analysis andnquantification showed that no seasonal effect and no trend over the year were detectable. The law ofnpropagation of uncertainties is applicable for uncertainties estimation. The method has then beennapplied to all measured storm events. This study confirms the interest of long term continuousndischarge and turbidity time series in sewer systems, especially in the perspective of wet weathernquality modelling.