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6. CLASSIFYING HEAVILY MODIFIED AND ARTIFICIAL WATER BODIES
6.1 Overview
In some cases, substantial modifications to the physical characteristics of surface water bodies have been made to accommodate uses like navigation, water storage, flood defence and land drainage. Such modifications may be preventing the bodies achieving good ecological status. If this is so and the bodies cannot be restored to 'good' ecological status without significant adverse effects on those uses, the WFD allows the bodies to be designated as heavily modified water bodies ( HMWBs). Man-made water bodies, such as canals, that have been created where no natural water body previously existed, can be designated as artificial water bodies
The principal objective for such water bodies is to aim to achieve good ecological 'potential' by 2015. Further details of this process are described in our Policy Statement, " Principles for setting objectives for the River Basin Management Plan".
There are five classes of ecological potential defined in the WFD. The classes are defined in terms of how much the ecological quality of such water bodies deviates from the best that could be achieved (i.e. the maximum ecological potential) without putting in place mitigation (relating to the modified or artificial physical characteristics) that would have a significant adverse effect on the relevant use or on the wider environment.
Although the WFD does not require us to distinguish between bodies at good and maximum ecological potential when presenting classification maps, we expect SEPA to take steps to make this distinction, in order to protect those water bodies from deterioration.
For the purposes of determining whether a heavily modified water body is at good or maximum ecological potential, SEPA cannot simply apply the normal standards and condition limits for hydromorphological quality elements or biological indicators that are sensitive to hydromorphological alterations. This is because a failure of these standards and condition limits would not necessarily mean that a water body was failing to achieve good or even maximum ecological potential. Instead, if all mitigation that could be taken to address the adverse ecological effects of a body's modified or artificial characteristics has been taken, SEPA should:
(a) classify the body's hydromorphological characteristics as being sufficient to enable the achievement of good or maximum ecological potential; and
(b) provided no other pressures (e.g. discharges) on the water body are causing a failure of any of the standards or condition limits for 'good', classify the water body is achieving good or maximum ecological potential.
6.2 The classification process
The classification of the ecological potential of heavily modified and artificial water bodies requires identification and assessment of the following:
- the modifications and artificial characteristics of the water body concerned that are preventing the achievement of good ecological status;
- the mitigation measures already taken in relation to those characteristics and whether they adequately mitigate the identified impacts; and
- whether there are other mitigation measures which could be put in place without significant adverse effects on the use or uses, or on the wider environment.
Most of the other steps in the process are similar or identical to those described in Section 4 for classifying the ecological status of other surface water bodies. The steps are summarised in Annex G. Further details about appropriate mitigation measures can be found in UKTAG's report on Heavily modified water bodies classification.
The classification of the chemical status of heavily modified and artificial water bodies follows the same process described in Section 4 and detailed in Annex D for other surface water bodies.
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