In order to effectively manage the water environment of the Tweed catchment, it is necessary to have information on rainfall and river flows throughout the catchment. This information is gained by analysing data from a network of measuring sites and river gauging stations situated throughout the Tweed system.
The monitoring network
Within the Tweed catchment there is a network of rain gauges providing valuable assessments of the intensity and duration of rainfall likely to result in flooding. SEPA operate 12 gauges manually read each day by observers, as well as 21 automatic recording rain gauges, most of which are on telemetry systems thus providing real-time data.
The measurement of river flow is crucial for pollution control and flood warning. The greater the flow, the greater the level of dilution available to enable the river to assimilate effluent discharges into it. SEPA operate 37 river monitoring stations that record river level and, from these recorded levels, produce 15 minute flow figures in m³/s. An important use for these stations is to provide data and warnings for the flood warning system covering the Tweed area. SEPA communicate with these sites using the public telephone system and mobile phone network. 20 of the monitoring sites have cableway systems allowing measurement of flows at medium to high levels when wading would not be possible. If flows in non-monitored catchments are required, they are calculated by SEPA’s water resource department using specialised software packages.
The importance of river flow
The extremes of river flow are of great importance. For example, when designing for sewage works or trade effluent treatment plants, a good knowledge of dry weather and drought flows is essential, since it is at these times that rivers are likely to be under most stress in their ability to absorb the impact of any discharge. At the other end of the spectrum, the occurrence of floods can cause damage to structures and land and endanger life.
Reservoirs and river flows
Water supply reservoirs in the headwaters of several Tweed tributaries, such as the Megget and Whiteadder, allow river flow to be enhanced, especially during the drier summer months. The prime purpose of these reservoirs is to collect and store water for water supply but they also return water back into the river from the reservoir, a process known as “compensation” water. Due to its involvement in pollution prevention, rainfall measurement and rainfall gauging, SEPA has developed a role as impartial negotiator in agreeing the amount of compensation water with water supply interests, as well as rates of discharge and so forth. Modern policy on compensation water has moved away from the old system where a fixed amount of water was released daily from the reservoirs throughout the year. Under the new system, higher rates of flow are released in the summer, with occasional releases of even larger flows, known as freshets, which may last a day or more. Freshets are released when it would be beneficial to the river, for example, after a prolonged period of low flow rates. The ability to provide adequate compensation flows throughout the year is generally beneficial, and in a dry summer, flows in sections of the Tweed may be nearly 50% higher that they would have been if no reservoirs existed.
While flooding is a natural process it can be exacerbated by activities such as canalisation; riverworks; modification and diversion of rivers; land drainage; poor agricultural and forestry practices; or floodplain development. Addressing those land management practices that increase flood risk will aid effective and sustainable flood management. However, there is also a need to avoid short-term localised solutions and move towards a more catchment-based approach which does not transfer problems from one part of the catchment to another. Indeed, a catchment-based approach is required by EU legislation, such as the WFD and Floods Directive, as is the need for exploring land management practices that allow the natural processes of a river to function (Sustainable Flood Management).
The legal position between Scotland and England with regard to flood prevention is different, yet they are both subject to the over-arching EU Floods Directive. For flood prevention in Scotland, SEPA and local authorities take the lead role, while, in England, this responsibility falls to the EA and Lead Local Flood Authorities. Development control and planning responsibilities, which are important components of flood management, are also split within the Tweed catchment between Scottish Borders Council on the Scottish side and Northumberland County Council on the English side. The Tweed Cross Border Advisory Group has been formed, under the Floods Directive, to address any cross-border issues arising. Both SEPA and the EA operate flood monitoring schemes in their respective areas, as well as flood warning services – Floodline in Scotland and a flood warning sign-up service in England. Information is readily exchanged where flooding occurs within the cross-border Tweed catchment, with regular updating until the flood situation has passed.
The law relating to river water abstraction in England and Wales is quite different from that in Scotland. Furthermore, the laws that regulate abstraction in the catchment of the English River Tweed are currently different from those in the rest of England and Wales. Since the licensing of abstractions started in 1963, an abstraction licence has not been required to authorise abstraction from surface waters in the catchment of the River Tweed, no matter how large the abstraction. However, licences are required for groundwater abstraction. Under the provisions of the Northumbrian Water Act (NWA, 1981) a licence is required for any groundwater abstractions which take more than 227 m3/day (50,000 gallons per day) from underground strata or a spring.
Most of the River Till and its tributaries are a Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC). As the EA cannot license abstractions, Natural England consent surface water abstractions in these areas as potentially damaging activities, under the legislation that applies to SSSIs and SACs. Once the Water Act 2003 comes into force in the English Tweed catchment, both ground and surface water abstractions within the Till Catchment will be brought in line with the rest of England and Wales. Whether or not a licence is granted depends on the amount of water available after the needs of the environment and existing abstractors are met and whether the justification for the abstraction is reasonable.
In Scotland, abstractions are regulated by the Water Environment (Controlled Activities) (Scotland) Regulations 2011 – more commonly known as the Controlled Activity Regulations (CAR) – and their further amendments. In terms of regulation, an abstraction requires authorisation, whether it is carried out on a permanent or temporary basis. This authorisation will be at one of 3 levels, General Binding Rules, Registration or Water Use Licence, depending on the nature of the abstraction activity.