The River Gelt rises on the western slope of the ridge between the watersheds of the Eden and the South Tyne rivers. It is just under 14 miles long before it joins the Irthing, which in turn. after a further 3 miles, enters the Eden near Newby. Before the waterworks was built, the waters of the Gelt were not used for manufacturing purposes, and the only mill along its course was a small corn mill near High Gelt Bridge, which had been out of use for some years by the time plans started to be drawn up.

The head waters of the Gelt were – and still are - known as Old and New Waters, two streams which drain an area of open moorland of about 7,500 acres. They flow in a northerly and westerly direction for 3 miles, with Old Water being to the north of New Water. Both form one stream – or the Gelt – just east of Geltsdale House. It is 11 miles as the crow flies to Carlisle Cathedral.

There were many advantages of choosing this as the new site to supply water to Carlisle. One was the fact that the gathering ground of New and Old Waters was almost completely free of contamination by livestock or human habitation (there was just one cottage in the area). Also, there were several other good springs in the area, which were to be incorporated into the collection of the water – Tarnmonath, Priest, Leach, Sheepwash, Pit Bank, Bridge East and Bridge West. As well as this, the junction of the two waters was about 725 feet above sea level, meaning that gravity (rather than pumping) could be used to collect and move the water.

Water is still abstracted here today, high up in Geltsdale, before being piped down the valley to the reservoir, which at 450 feet above sea level, means the water has been able to fall almost 300 feet in three miles. Water is still collected from various springs, New and Old Waters, “mixed” at the collecting or metering house (which still stands) in Geltsdale and then flows by gravity down to the reservoir, which acts as a storage for it. An agreement was put in place a hundred years ago that a minimum of 1.5 million gallons had to still flow down the Gelt following abstraction – and a gauge at Hynam Bridge measured this. The small stone measuring house is still there today, while careful controls make sure that enough water still flows down the Gelt to support fish stocks of brown trout, migratory salmon and sea trout.

Hynam Bridge
Hynam Bridge Gauge (Environment Agency)
Hynam Bridge Pipework

One of the revolutionary features of the design of the system – for its time – was the building of a storage reservoir (in Castle Carrock) in a separate location and away from the collection point (in Geltsdale). This was partly because of concerns over how big the reservoir would need to be in Geltsdale to deal with the potentially enormous volume of water collected there. But also, the geology wasn’t suitable in Geltsdale for collecting and then importantly keeping the water – it was carboniferous and would therefore “leak” too much. Further down, the rock was far more impermeable, and therefore suited to collecting water, in the shallow valley of Castle Carrock Beck. And so, a 20inch diameter cast iron pipe was built, three miles long, starting at the metering house and then snaking along the course of the Gelt, crossing the river at Hynam Bridge, winding its way through the fields, skirting around Garth Marr and Garth Foot, and then running parallel to the eastern side before entering the reservoir at its far end where you can still hear the water gushing in today after its curving journey from Geltsdale. You can track the pipe if you look carefully at gaps in hedges, spot manhole covers, and walk along the far side of the Gelt. Look over the lefthand side of Hynam Bridge after walking down from Jockey Shield for clear evidence of its path.

Look closely at the maps, though, and you will notice that little Castle Carrock Beck, which for thousands of years happily gurgled its way along its shallow valley from the south, suddenly disappears for the length of the reservoir before reappearing at its northern end. We all know, of course, that it then passes under the small road bridge before winding its way along the fields and behind the back of the school. But in 1897, it was decided that its water was inferior to that which would be collected from Geltsdale – primarily because of its exposure to agricultural contamination. So the remarkable decision was taken to channel it underground in a circular concrete culvert, five feet in diameter, around the eastern side of the reservoir, to keep it completely separate from the water being piped in from Geltsdale. Crane your neck to the left next time you rest your elbows on the wooden farm gate which directly overlooks the dam, and you’ll see the culvert emerge just above the dam in an open 30 yard stretch. Look closely and you’ll see it suddenly re-emerge on the downside of the dam before the Beck is carefully channelled away from the Waterworks.

The reservoir itself covers 43 acres and has a maximum depth of 33 feet. The dam needed foundations which went down 130 feet – much further than was first planned - which added to the cost too. The trench was filled up with concrete at the bottom, then clay puddle to the top, with a sandstone embankment. Look at the dam from its eastern end and you will see the grassy bank sloping down at an angle to the right. The angle of the dam on the opposite side, the water side, lined by stone, is set at exactly the same angle for balance – it’s not vertical. Regular inspections take place to ensure that there is no damage or weakness, even though the throngs of rabbits may have other ideas.

Converting Castle Carrock Beck valley into a reservoir basin was straightforward. The only work needed to be done was to scrape off peat in certain places where it was exposed – it was then dumped to the west of the reservoir. For the most part, though, it was just the natural earth found in the valley that formed the bottom of the reservoir.

At the reservoir, the water is fed in at its southern end and then drawn off by the iconic Valve or “Draw off” tower at the works end of the reservoir. Many people will recognise its silhouette as they sup a bottle of Geltsdale beer. The tower can take water from various levels to allow flexibility and maintain a constant quality of supply to the water treatment works.

Geltsdale waterworks was finally brought into operation on August 16th 1906 after the completion of the intakes in Geltsdale, the pipeline and the filter beds. Purification was originally by seven slow sand filters, each capable of filtering 300,000 gallons a day. It was to be a further three years before the reservoir itself was finally finished and officially opened – on July 22nd, 1909. It was designed ultimately to supply 2.4 million gallons per day, starting with a daily consumption of one million gallons.