Rivers Agency explores the Lough Erne system

18 March 2010

Rising in Lough Gowna, Co Cavan, the River Erne flows through Fermanagh and onwards to Ballyshannon in Co Donegal.  At 100km long it drains a vast area of land, referred to as the Erne Catchment.   There is sometimes confusion that water also flows in from the Shannon however this is not the case, as Rivers Agency’s Alun Goodall explains.

“Think of a catchment as a dinner plate filled with water and imagine two plates side by side.  One is the Erne and the other is the Shannon.  While the plates are touching, no water is actually passing between them.  This is the same for our catchments as water cannot cross the boundaries due to a range of hills, so for example when Lough Erne flooded last November it was only water from the Erne, not the Shannon.”

The current system for managing the Loughs was set up in 1950 when the Erne Drainage and Development Act (NI) was passed.   With the Act came the introduction of a statutory minimum and maximum water level for the Lower Lough as well as a statutory minimum for the river through Enniskillen.   

An agreed narrower band of operating levels exists to avoid unnecessary fluctuations in Lough levels and these levels are maintained in consultation between Rivers Agency and the Electricity Supply Board (ESB).  To ensure that the Loughs are viable for their various users, a management committee of statutory bodies representing these users oversees activities in relation to the Loughs.   

“It’s an important balancing act,” continued Alun.  “Levels are controlled to try to achieve a good balance between flood alleviation and environmental considerations such as bird nesting and fish spawning, while facilitating those who use the Loughs recreationally.  We don’t want erratic fluctuations.”

The Upper Lough is maintained above 150 feet in order to accommodate boating and water recreation activities.  This level is managed by gates located between the two Loughs at Portora, however the gates are only required during spells of very dry weather.  

Water then leaves the system from the Lower Lough at Cliff.  Water is never stored here – it is passed through the turbines as soon as it is available, generating hydroelectric power.  The system also has the ability to deliberately spill excess water but this is only required when Lough levels are of a height which results in flows exceeding the capacity of the generating plant.   On average this situation only arises one or two times a year.

While boat navigation requires higher Lough levels during the summer months, in autumn the focus is to minimise the risk of flooding and therefore levels are deliberately drawn down to increase the amount of storage for winter rain fall.  

Where the difficulties lie is that there is no accurate long term outlook of the weather.  Realistically weather patterns can be forecasted five days in advance and from this Rivers Agency works with the ESB to decide what action will be taken.

“The situation that we’re currently faced with is that the water level in the Upper Lough is approximately eight inches lower than usual for this time of year.  Since December there has been nearly 50 per cent less rainfall compared to the long term average, resulting in river flows reducing to a trickle and very little flowing into the Lough.  As a result, the gates were closed and generation stopped on 5 March,” added Alun.

“Admittedly this seems hard to imagine when just four months ago the situation was very different.  However what the situations have in common is that both are a result of unusually extreme rainfall patterns.  

“Last November more than three times the average rainfall fell in Fermanagh.  Despite Lough levels being reduced to their absolute minimum beforehand and the maximum amount of water being spilled out, the sheer volume of rainfall meant flooding was unavoidable.”

So what are the benefits of the system?  Importantly, it relieves Fermanagh from the frequent and severe flooding that it experienced through the centuries.  What Fermanagh witnessed in November would have been a much more common occurrence beforehand.  While there is still occasional flooding, the engineering works carried out in the 1950s have massively improved drainage so flood levels and their duration have greatly reduced.   

The system also promotes sustainable energy by generating up to 65Mw of hydroelectric power each year.  That’s the equivalent energy consumption of 38,000 houses.

And the future?  “Continuing to manage flood risk,” said Alun.  “It’s important to remember that the River Erne is a natural river.  It therefore has natural floodplains and unfortunately flooding is an inevitable consequence during extreme conditions.

“Essentially we’re only tinkering with nature.  The area which flooded last November sits on the floodplain so our focus has to remain on managing flood risk,” he concluded.”