is a

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

in the traditional county of

Inverness-shire Inverness-shire () or the County of Inverness, is a Counties of Scotland, historic county in Scotland. It is named after Inverness, its largest settlement, which was also the county town. Covering much of the Scottish Highlands, Highlands and s ...

in the

Scottish Highlands The Highlands (; , ) is a historical region of Scotland. Culturally, the Highlands and the Scottish Lowlands, Lowlands diverged from the Late Middle Ages into the modern period, when Scots language, Lowland Scots language replaced Scottish Gae ...

. Its name literally translates from

Scottish Gaelic Scottish Gaelic (, ; Endonym and exonym, endonym: ), also known as Scots Gaelic or simply Gaelic, is a Celtic language native to the Gaels of Scotland. As a member of the Goidelic language, Goidelic branch of Celtic, Scottish Gaelic, alongs ...

as "Big Loch". It occupies much of the wide floor of Stratherrick which runs roughly parallel to

Loch Ness Loch Ness (; ) is a large freshwater loch in the Scottish Highlands. It takes its name from the River Ness, which flows from the northern end. Loch Ness is best known for claimed sightings of the cryptozoology, cryptozoological Loch Ness Mons ...

, around to its southeast. A generally shallow body of water above Loch Ness, Loch Mhòr achieves a depth in excess of towards its southern end. It is nearly in length, with a maximum breadth of and mean breadth around . In its middle reaches, a broad and shallow embayment on its southeastern shore contains a scatter of islets. The loch is elongated with a very irregular form, the eastern shore broken up by multiple bays. Loch Mhòr was originally two separate lochs, Loch Garth in the southwest and Loch Farraline in the northeast. The reservoir was formed in 1896 by the construction of two dams, raising the water level by up to above the level of Loch Farraline and joining the two lochs into one. This was created for a hydro-electric scheme and associated aluminium smelter at Foyers, although the smelter closed in 1967. Loch Mhòr is divided in the middle by a causeway carrying a minor road. A

masonry dam Masonry dams are dams made out of masonrymainly stone and brick, sometimes joined with mortar. They are either the gravity or the arch-gravity type. The largest masonry dam in the World is Nagarjuna Sagar Dam, Andhra Pradesh and Telangana, in ...

was constructed across the River Gourag, long and high. A longer

embankment dam An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil or rock. It has a semi-pervious waterproof natural covering for its surface ...

was constructed at Garthbeg, long and high. This only had a freeboard of and was known to leak. The main rivers flowing into Loch Mhòr are the Aberchalder Burn, originally a tributary of Loch Garth, and the River E, which was diverted for the original hydro scheme by construction of the Garthbeg dam. The waters of the loch empty as the River Gourag below the Loch Mhòr dam at its southwestern end. This short river becomes the Allt an Lòin downstream of the former confluence with the River E, then joins the River Foyers which empties into Loch Ness via the Falls of Foyers. The Loch is still used as the upper reservoir for the 300 MW Foyers

pumped-storage hydroelectricity Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing (electrical power), load balancing. A PSH system stores energy i ...

facility.Foyers Hydro-Electric Power Scheme
Gazetteer for Scotland. Retrieved: 13 November 2015. As part of the construction of this, some of the flow of the River Fechlin was diverted through an aqueduct. This increased the catchment area by . The catchment of Loch Mhòr, including the River E, was previously . In the late 1960s early 70s, a flood study commissioned by SSE identified an overtopping risk at Garthbeg embankment dam. Therefore the spill weir at the main Loch Mhòr dam was lowered by . In May 2018, an inspection under Section 47 of the Reservoirs Act 1975 found issues with this spillway, therefore the reservoir was not to exceed 193.83 m AOD ( below top water level). Repair works to the weir were carried out between May 2021 and January 2022. In 2017, options to increase the reservoir capacity were investigated by SSE, by replacing the dam spillway and increasing the top water level by . However, increasing the water level by was likely to flood riparian properties. The weir was therefore replaced at the same level, but future proof to allow a 0.5 m increase subject to obtaining land ownership and rights for this level of inundation.

References

{{DEFAULTSORT:Mhor Mhor Mhor Freshwater lochs of Scotland