Table 8.7 Criteria used to determine the magnitude of marine water quality effects. Magnitude


Definition High


Large scale change to key characteristics of the water quality status of the receiving water feature. Water quality status degraded to the extent that a permanent or long term change occurs. An ability to meet (for example) EQS is likely.


Medium


Medium scale changes to key characteristics of the water quality status taking account of the receptor volume, mixing capacity, flow rate, etc. Water quality status likely to take considerable time to recover to baseline conditions.


Low


Noticeable but not considered to be substantial changes to the water quality status taking account of the receiving water features. Activity not likely to alter local status to the extent that water quality characteristics change considerably or EQSs are compromised.


Negligible


Although there may be some impact upon water quality status, activities predicted to occur over a short period. Any change to water quality status will be quickly reversed once activity ceases.


8.4.3.3 Impact significance 54.


Impacts are assessed by relating the magnitude of an effect to the sensitivity (or value) of the receptor, which in this instance is water quality. This relationship is presented in an Impact Assessment Matrix in Table 8.8.


Table 8.8 Impact Significance Matrix Sensitivity


High High


Medium Low


Negligible


Major Major


Moderate Minor


Medium Major


Moderate Minor


Negligible


Magnitude Low


Moderate Minor Minor


Negligible Negligible Minor


Negligible Negligible Negligible


No change


No Impact No Impact No Impact No Impact


55.


As with the definitions of magnitude and sensitivity, the matrix used for a topic is clearly defined by the assessor within the context of the marine water and sediment quality assessment. The impact significance categories are divided as shown in Table 8.9.


Preliminary Environmental Information May 2014


East Anglia THREE Offshore Windfarm


Chapter 8 Marine Water and Sediment Quality Page 19


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