3. Index screening methodology
The method used in this paper screens all the indexes according to the exceeding standard rate and
pollution contribute rate during the monitoring period.
The exceeding rate is used to judge the exceeding situation of some index in the certain monitoring
period. Higher exceeding rate indicates that this river is the key management object as its exceeding
frequency is much higher. The calculation of exceeding rate is the ratio of the number overweighs the V
standard index in GB3838-2002 and the total monitoring number of this index during certain monitoring
period.
And the pollution contribute rate is used to indicate the contribution of certain index to this water area,
if the value is higher, which means the pollution contribution is much bigger, that is, this index is the main
pollution index. The formula of the pollution contribute rate of certain section indicator (except the pH
value) is,