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Chapter eight
THE IMPOUNDMENT CONTROL REGIME
Directive's requirements
8.1 The Directive's requirements for controls over impoundments are the same as for abstraction - a register of impoundments and prior authorisation/licensing and with exemption from controls for impoundments that have no significant effect on water status. The impoundment of estuarine or coastal water will also need to be controlled where it is affecting water status. It is important to remember that there is flexibility in the Directive so that controls can be applied in a way that takes account of the important social, economic and environmental needs served by impounding structures.
Environmental Impacts of Impoundments in Scotland
8.2 Impoundment is the holding of water behind an artificial barrier. Reservoirs are the most obvious example but a small storage pond fed from a river would also be an impoundment. We estimate that there could be 5-10,000 impoundments in Scotland. Of these about 1000-1,500 will be large public supply or hydro- electricity reservoirs. The rest will be smaller impoundments used by business and agriculture. The effects of an impoundment will be variable, depending on the size, design and operation of the impoundment and the sensitivity of the location. They tend to have effects both upstream and downstream, interfering with the normal pattern of the flow of water and the movement of sediment. They may also be a barrier for migrating fish and other animals.
The regime
8.3 Some existing legislation applies to impoundments, principally, the Salmon (Fish Passes and Screens) (Scotland) Regulations 1994 which are designed to ensure that impoundments do not impede the passage of migratory salmon. Hydro-electricity schemes are regulated through their various establishing Acts and the Electricity (Scotland) Act 1989. Reservoirs for public supply are also regulated under the Water (Scotland) Act 1980. Planning controls and environmental impact assessment procedures will also apply to many impoundments. In addition, under the Reservoirs Act 1975, reservoirs with a raised capacity of more than 25,000m 3 need to be registered with the relevant local authority in order to ensure that they are maintained for safety reasons.
8.4 Collectively, these various regimes do not add up to a comprehensive system for prior authorisation of impoundments to meet environmental objectives. A new system is needed. Our ideas for a system of impoundment control are very similar to those for abstraction and are described in detail below.
Water Resources Management Strategies
8.5 The environmental effects of impoundments are even more complex than abstractions, with complicated effects occurring both upstream and downstream of the impounding works. As with abstractions, it is best to plan the management of impoundments at catchment level. We suggest that both abstractions and impoundments should be managed together on the basis of water resource management strategies.
Thresholds
8.6 Again, as with abstractions, it would be useful to set a threshold for applications for determination. Any impoundment associated with an above threshold abstraction (20m 3 per day) may well be significant and so we feel that this same threshold should apply. Similarly, the owner or occupier of any impoundment large enough to be registered under the Reservoirs Act should also apply for a determination. We know that there are impoundments that are no longer being used and we suggest that their current owners or occupiers should also apply for a determination if they were designed to supply more than 20m 3 per day.
8.7 It is by no means certain that every impoundment over these thresholds will need to be subject to controls. Each one will be considered on its merits. The general principles described in Chapter 4 would apply so that the regulator would be able to bring impoundments below these thresholds into the control system where necessary. There would also be a general requirement to notify the regulator of all impoundments to inform the water resource management strategies.
8.8 In many cases, there is scope for mitigating the environmental effects of impoundments through the way they are operated. This would include operations such as the release of compensation flows, including artificial spates, fish passes and de silting and sediment control mechanisms Therefore, we suggest that controls should apply to the operation as well as the construction of impoundments.
Information from Impounders
8.9 We think that it is reasonable to ask all impounders to supply some basic information about their impoundment and how it is operated. For those that are subject to more than simple registration more detailed information will be required. This would include some assessment of the environmental effect of the impoundment.
Simplified Controls
8.10 As with abstractions, we feel that there is scope to reduce the regulatory burden on those who own or keep impoundments through the use of general binding rules and flexible licences such as combined abstraction and impoundment licences and single licences covering multiple impoundments. Similarly, we believe that management agreements may offer benefits where a number of different impoundments are operated together or where impoundments owned by separate operators interact in a complex way.
8.11 The flow diagram in Table 7.1 summarises how the abstraction and impoundment regimes might operate in practice. We would welcome your views. Should we proceed to design the system along the lines described above? Is there any scope for taking a different approach? How should the new regime interact with existing regimes?
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