Environmental Engineering Reference
In-Depth Information
lower range of variation in the pollution load computed, than the ones in the positive zone
(overestimation of actual values).
The simple method allows the use of weighted runoff coefficients, which give a more
accurate estimation of the net rain volume. Their determination is important in cases of
mixed pattern land use practices, which have different cover characteristics, slopes,
vegetation, etc. It requires the subdivision of the total drainage area on several parts with
relatively uniform characteristics and the assignment of area-specific runoff coefficient to
each one of them. Then, the weighted coefficient will be calculated by equation 4.5.
(4.5)
where R
w
= weighted runoff coefficient; R
i
= area-specific runoff coefficients; A
i
= part
of the total drainage area with uniform cover characteristics.
The determination of the net runoff by the SNC curve method (Schulze et.al. 1993),
described in more detail in Chapter 5, accounts for more factors, which would influence
the accuracy of determination, and if the input data with respect to these parameters is
available, it could lead to more accurate results. In both cases, the application of GIS
could provide very useful data about the drainage area, thus improving the accuracy of
the process and could reduce considerably the time required for the data handling and
analysis.
The average runoff quality parameters determined during the study and presented in
section 3 could be useful for further investigation of this problem, but could not be
accepted as a reliable basis for actual pollution loads estimation, especially regarding
parameters showing flushing effects.
