I have discharge (m3/sec) and concentration (mg/l) of pollutant of that particular event where sample has been taken in a irregular interval. So, how to calculate Delta t for the equation.
Another problem is if a event means two dates for example 26/1/2000 with start time 12:30 and end date is 27/1/2000 and end time is 10:00.
Can you please give us more details and context ? What is EMC and what Δt in which equation ?
Event Mean Concentrations (EMCs) describe the average concentration of a given pollutant for an individual storm event (Park, Swamikannu & Stenstrom 2009).
EMC=
∑ (Q)(C)∆T/ ∑ (Q)∆T
where C(t) is the concentration expressed in (mg/L), t is time; Q(t) is the measured runoff rate, usually in (L/s); Δt is the time interval (s), and t1 and tf are respectively the times at the start and end of the event.
If pollutant levels are being calculated for a catchment, a mean value of the site EMCs can be used, or alternatively a Site Mean Concentration (SMC) can be calculated, being the total load from the catchment divided by the total flow for a given number of events.
EMCs provide a simple method of pollutant washoff load modelling when coupled with a hydrological model. For example, the Stormwater Management Model (SWMM) User Manual by Rossman (2015) includes reference EMCs for a range of pollutants, originally sourced from USEPA (1983).
You can modelize C(t) and Q(t) by polynomials or cubic splines and use calculus to determine EMC = integral [C(t)•Q(t)•dt] / integral [Q(t)•dt] between ti and tf.
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