Environmental Engineering Reference
In-Depth Information
et al. 2002, Sansalone et al. 1997). For this specific study, the flushing coefficients were
calculated by equation (4.4), based on the total duration of the storm event and
correspondingly □(Q
i
/□Q
i
)=1. The flushing coefficients, which have a value > 1, indicate
the presence of flushing effect with respect to the studied pollution constituent. Actual
pollution loads represent the sum of the specific load for each time interval, calculated
based on the corresponding contaminants concentrations and flow rates. For the purpose
of comparison, pollution loads were also calculated, based on the total runoff volume
discharged during the storm event and pollutant constituents represented by average
concentrations and EMCs.
(4.3)
(4.4)
where C
i
, P
i
and Q
i
are the contaminant's concentration, pollution load and flow rate,
respectively, for each time interval.
The results in Table 4.3 show and confirm that the flushing effect is associated mostly
with particulate material. The parameters, which have a flushing coefficient higher than
1, also have EMC concentrations, which are considerably higher than the mean
concentrations. This is associated with the erosive capacity
Table 4.3. Characteristic parameters of a single
storm event (wet weather).
Constituents
COD TSS
TDS
Ammonia
TP
Mean concentrations (mg/l)
289
327
134
0.21
0.48
EMC (mg/l)
420
379
126
0.20
0.65
Pollution load - EMC (kg)
7106
6413
2271
4
11
Pollution load - average concentrations (kg)
4887
5533
2132
4
8
Flushing coefficient
1.25
1.13
0.68
0.55
1.03
of the rainfall event and the increased rate of pollutant transport during peak flow
conditions, due to the increased suspended solids concentrations in runoff and other
pollution constituents associated with them. This result has a significant implication
regarding the monitoring and abatement strategy of diffuse pollution. It shows the need
for the estimation of EMC regarding constituents associated with suspended material,
which would influence considerably, the pollution loads estimation to natural water
bodies and corresponding effects and impacts. The application of average concentrations
with respect to particulate pollutant constituents leads to a considerable underestimation
of the pollution loads contributed to receiving water bodies. A more detailed analysis of
the implications due to errors in the estimation of pollution loads is presented in section
4. In addition, the results obtained during the study of this specific single storm event,
show that the removal of suspended matter from the runoff before it is discharged into the
receiving water body could reduce substantially the pollution loads regarding COD, and
