Lower Bann - Water Quality
Water Quality in rivers is classified using both chemical and biological monitoring techniques. For each system of measurement there are six water quality classes which are; very good, good, fairly good, poor and bad. To view the results for the Lower Bann and its tributaries please click here.
The Bann Estuary is not classified in the same way due to the salt water environment. The Coleraine Sewage Treatment Works (STW) discharges most of the effluent having received primary and secondary treatment. At times, however, the system is overloaded and effluent is discharges to the estuary having received primary treatment only. This arises as a consequence of the sewage system being linked to storm drains and overloading the treatment works during periods of wet weather. This causes a water quality problem both within and on Castlerock beach which fails to meet Blue Flag standard because of the Coleraine STW, and other industrial and storm drain discharges in the estuary.
Lower Bann - Water Levels
A number of issues arise from the management of the sluice gates in the Lower Bann. Within the river, for example, abrupt changes in water level, including freshet release, can cause difficulties for anglers and boaters. Fish movements are sensitive to river flows and the Lough Beg grasslands can be re-flooded in spring destroying the nests of breeding waders. Water level management also impacts throughout the Lough Neagh wetlands. For example, wetlands can be negatively affected by excessive droughts but damage can also be caused to ground and nesting birds by unseasonal floods. It is not possible to address water levels issues simply in a nature conservation of fishing context as there are enormous implications for eel fishing, navigation and farming throughout the Lough Neagh catchment as well. Often the needs of these legitimate interests conflict.
Drainage and Navigation
Water levels on Lough Neagh and flows in the Lower Bann are controlled by a system of sluice gates and weirs put in place as a result of a number of drainage schemes. A system of locks makes it possible to navigate along the full length of the river.
Although there had been earlier piecemeal attempts the first large scale drainage scheme was the McMahon Scheme carried out between 1846 and 1856 with a view to reducing the level of Lough Neagh and making the river navigable. This involved building 5 locks and weirs, the removal of a rocky shoal at Portna and limited dredging of the Lower Bann. Because of the engineering compromise between drainage and navigation requirements the McMahon Scheme was considered less than successful. Another drainage scheme, the Shepherd Scheme carried out in the 1930s involved deepening, widening and straightening of the drainage channel and replacing the fixed weirs at Toome, Portna and the Cutts with sluice gates. In response to continuing pressure to alleviate flooding around Lough Neagh the water level was further lowered in the 1940s and 50s by adjusting the management regime of the sluice gates at Toome. The net effect of these drainage schemes was a lowering of the Lough Neagh water level by about 3 metres and a reduction in the natural range of high and low water levels.
The Lough Neagh & Lower Bann Drainage and Navigation Act
Water levels in Lough Neagh are prescribed through Lough Neagh (Levels) Schemes made under section 1 of the Lough Neagh & Lower Bann Drainage and Navigation Act (NI) 1955. The current Lough Neagh (Levels) Scheme 1955 specifies that the water levels of Lough Neagh should be maintained between 12.45 metres and 12.60 metres above sea level as far as conditions of rainfall, wind and other natural causes allow.
Sluice gate operation
The sluice gates are managed by Rivers Agency with the aim of maintaining the level of Lough Neagh within the 15 centimetres control range whilst at all times maintaining an adequate flow in the Lower Bann (when the sluice gates are closed a minimum flow to the Lower Bann is constantly discharged through a fish pass beside the sluice gates).
The water level in Lough Neagh is controlled by the Toome sluice gates. Within the statutory ‘control’ range of 12.45 metres and 12.60 metres above sea level Rivers Agency strive to maintain a ‘operational’ level of 12.47 metres during the winter months when the risk of lough draw-down is least and flood risk is high and 12.57 metres during the summer months when the opposite applies. The operating levels both provide a 25 millimetre margin within the respective closest limits of the control range in order to provide the necessary leeway. In practice it is impossible to consistently keep Lough Neagh levels within this narrow range because of natural floods and droughts.
Lower Bann Navigation
The Lower Bann Navigation operated commercially from the 1850s to 1929 when the Lower Bann Navigation Trust was abolished and responsibility was passed to government and thence to Rivers Agency today. There are locks at Toome, Portna, Movanagher, Carnroe and the Cutts. The navigation is maintained to provide a minimum depth of 1.5 metres along its full length through the placement of weirs, the management of sluice gates and limited dredging.