Middle section

The railway and road follow the northern edge of Loch Luichart. Construction of the dam at the eastern end of the loch required some 2 miles (3.2 km) of the railway to be relocated, because the level of the loch was raised, and a new station was built, which opened on 3 May 1954.^[7] Mossford hydro-electric station is sandwiched between the road and railway a little further to the east, and water from Loch Fannich passes through the station and discharges into Loch Luichart. There is a scattering of houses in the area, which form the hamlet of Lochluichart. The Allt Coire Mhuilidh flows southwards and into the loch near the hamlet of Corriemoillie, after which the road and railway are separated from the loch by a range of hills, the highest of which is Cnoc na h-lolaire at 1,161 feet (354 m). The loch turns to the south, and the dam is to the north of Little Scatwell.^[2]

Below the dam, Allt a' Ghlinne joins the river on its right bank. A bridge carries the minor road from Little Scatwell, and immediately afterwards is Luichart power station, fed with water from Loch Luichart by a tunnel. The next tributary is the River Meig, which joins on the right bank. It rises as a series of springs and streams in Glencarron and Glenuig Forest, close to the source of the River Bran, but on the southern slopes of the hills. It passes through Gleann Fiodhaig and heads in a north-easterly direction to reach Loch Beannacharain. A minor road runs along the northern shore of the loch,^[2] which contains an artificial island at its eastern end, on which a prehistoric crannog settlement was built.^[8] Below the loch the river is joined by Allt Gleann Chorainn on its right bank, and then by Allt Gleann Meinich on its left bank. It turns to the east near the hamlet of Dalnacroich, where the wide valley is known as Strathconon. At Bridgend it is crossed by a bridge with three arches, approached by a causeway with six more arches. The structure dates from the early to mid-19th century.^[9] It carries the minor road that runs along Strathconon across the river to its southern bank. The river then enters the artificial Loch Meig, created by the dam at its eastern end, and passes through a natural arch before it joins the Conon.^[2]

Eastern section

The river continues eastwards to reach Loch Achonachie. On its southern bank is Orrin power station, which receives its water supply from Orrin Reservoir, an artificial loch on the River Orrin. Loch Achonachie was created by constructing a concrete mass gravity dam at its eastern end. It includes a Borland fish pass, to enable migrating fish to reach the upper reaches of the river, with a single-storey turbine hall and two-storey office block built into the dam structure. The architect was James Shearer, and the building is dated 1955.^[10] To the south of the dam is the Fairburn estate, 1,100 acres (445 ha) of designed landscape, created in the late 18th and early 19th century, before it was remodelled by John Stirling in the late 19th century.^[11] As well as remodelling the park, he built a Baronial mansion house in 1877–78. Known as Fairburn House, it was designed by Wardrop and Reid, and most of it has three storeys, although it includes a five-storey tower.^[12]

The Black Water joins on the left bank, after which the A832 road crosses at Moy Bridge, running from a junction with the A835 road on the north bank of the river to the village of Marybank, to the south. Moy island is formed where the channel splits,^[2] and then the north bank is the southern edge of the Braham estate, 1,295 acres (524 ha) of designed landscape. It was created in the 17th century, improved during the following two centuries, and hosts an extensive collection of specimen trees and rare species.^[13] The river is joined by the River Orrin on its left bank before it turns to the north, and the large Dunglass Island is now the site of a hydroelectric station for the Brahan estate. Conon Bridge railway station is close to the northern end of the island, and the Far North Line crosses the river on Cononbridge railway bridge. It was designed by Joseph Mitchell and constructed in 1860–62. With five arches and a span of 77 feet (23 m), it is sharply skewed, and this was achieved by building each span as five narrow spans, which are staggered to achieve the skew.^[14]

The railway bridge is the normal limit of tides. Next to the northern end of the bridge is an octagonal tollhouse, built by Joseph W Mitchell in 1828, which was used to collect tolls from people using Thomas Telford's Conon Bridge, which has since been demolished.^[15] The A862 road now crosses the river on a newer bridge. Garrie Island sits in the river before another road bridge that carries the A835 trunk road. The river channel widens to the south of Dingwall, as it becomes part of the Cromarty Firth. There is a rifle range to the east of Dingwall, and much of the firth is marked as a danger area. Beyond the danger area, the A9 road crosses the firth on Cromarty Bridge. This was opened on 12 April 1979, and is nearly 1 mile (1.6 km) long. The deck is carried by 67 piers, designed to minimise changes to the tidal flows, in order to protect the feeding ground which are an important habitat for migrating birds. A maintenance programme costing £1.5 million drew to a close in June 2018.^[16] Beyond the bridge, the Cromarty Firth carries the waters of the Conon to the sea.^[2]

North of Scotland Hydro-Electric Board schemes

The Conon Valley was one of the early hydroelectric schemes implemented by the North of Scotland Hydro-Electric Board, although it was constructed in three phases between 1946 and 1961.^[22] After the board was created in 1943, Edward MacColl the chief executive produced a list of 102 projects which he thought could be built, from small ones to huge ones involving several neighbouring glens.^[23] The initial scheme for the Conon Valley involved using water from Loch Fannich, which would flow through a tunnel to Grudie Bridge power station on the banks of the River Bran just before it entered the western end of Loch Luichart.^[24] When the board promoted their second scheme, that at Tummel-Garry, members in the House of Commons attempted to get the findings of the tribunal which had considered objections to it overturned, but this was defeated. In the House of Lords, Lord Kinnaird wanted to introduce a similar motion, but was persuaded not to. However, he introduced a debate to consider the future of the board, at which various members of the house suggested that hydroelectric power was not needed in Scotland, as it would soon be replaced by nuclear power. Lord Kinnaird did not succeed, and during the debate Lord Westwood, the leader of the house, announced that all objections to the Fannich scheme had been withdrawn following discussions between the board and the objectors. It thus became the board's third project when it was authorised in late 1945.^[25]

The project involved the construction of several aqueducts and tunnels, to divert additional flow into Loch Fannich. The surface of the loch was around 820 feet (250 m) above ordnance datum (AOD), while the surface of Loch Luichart is 289 feet (88 m) AOD.^[26] A sloping tunnel was constructed from a point above the site of the power station to a point around 90 feet (27 m) below Loch Fannich. From there it was driven beneath the loch until there was only 25 feet (7.6 m) of rock between the excavation and the water. Rock was carefully removed above the tunnel to reduce the thickness to 15 feet (4.6 m), and a large sump was excavated, into which the final plug of rock would settle when it was blasted away. Two temporary concrete bulkheads and one steel bulkhead were constructed in the tunnel, to protect the tunnel and to ensure that debris from the rock plug would not be washed downstream. The final blast was successful, and was the second time that such a technique had been used in Britain. Balfour Beatty carried out the work, and had also been responsible for the first use of this technique, at Loch Treig for the Lochaber hydroelectric scheme.^[27]

The main tunnel was around 3 miles (4.8 km) long.^[28] No dam was built at Loch Fannich, as the water level could be drawn down by up to 50 feet (15 m), but five years later a dam was constructed, raising the surface level to 840 feet (260 m) AOD. At the lower end of the tunnel, water is conveyed to Grudie Bridge power station by a steel pipeline which is above ground. It is 8 feet (2.4 m) in diameter, but as it progresses downhill, the internal diameter reduces, and the walls get thicker. Close to the power station, it splits into two feeds, each of which supplies a 12MW vertical shaft Francis turbine. This was one of the last projects to use a surface pipeline, as the board were keen to reduce the visual impact of their schemes subsequently.^[29]

The power station building is clad in red Tarradale sandstone and was designed by the architect James Shearer of Dunfermline.^[30] Shearer had previously worked on other schemes, including the first to be commissioned at Nostie Bridge and had approached MacColl with the suggestion that the power station should be built of stone, to blend in with the surrounding architecture. MacColl readily agreed,^[31] but when it came to designing the structure at Grudie Bridge, he felt that construction in stone would be too slow and cost too much, and so prepared sketches for a concrete, steel and glass building. MacColl asked if Shearer had seen concrete buildings after they had been exposed to the Scottish weather for 20 years, and when Shearer admitted that he had not, MacColl organised a weekend visiting buildings to see how concrete weathered. As a result, the use of local stone to face large concrete buildings became a policy within the Board, and Grudie Bridge power station was redesigned as a consequence.^[32]

Second phase

The second phase of the scheme involved damming the River Vaich to form Loch Vaich and the Glascarnoch River to form Loch Glascarnoch, above the point at which the two rivers became the Black Water. To reduce the amount of cement used, the Glascarnoch dam consisted of a concrete gravity dam with earth fill. It was constructed by Reed and Mallik and was 1,753 feet (534 m) long, with a maximum height of 141 feet (43 m). The Vaich dam was smaller, at 843 feet (257 m) long and 123 feet (37 m) high, and was built by the same contractor. The flow into both lochs was increased by building aqueducts and tunnels to capture water from other watercourses, and a tunnel fed water from Loch Vaich into Loch Glascarnoch. The surface level of Loch Vaich is 840 feet (260 m) AOD, while that of Loch Glascarnoch is 827 feet (252 m) AOD. A 4.5-mile (7.2 km) tunnel from just above the Glascarnoch dam feeds water to Mossford power station, on the bank of Loch Luichart.^[33]

The waters of the River Bran, which flows into Loch Luichart, were exploited by building a small dam across the river below Loch Achanalt and Loch a' Chuilinn, to supply the Achanalt power station close to the Grudie Bridge station. This arrangement provides a head of 66 feet (20 m) and the station has a capacity of 2.4MW.^[34] A mass gravity dam was built at the eastern end of Loch Luichart, with a tunnel to supply water to Luichart power station at the western end of Loch Achonachie, which can provide 34MW from a head of 184 feet (56 m). Additional water was obtained by building a concrete gravity and earthfill dam across the River Meig, to form Loch Meig. The dam was built by Duncan Logan (Contractors), and was 585 feet (178 m) long with a height of 86 feet (26 m). A tunnel transfers water from Loch Meig to Loch Luichart. The final part of this stage was to construct a dam across the River Conon at Torr Achilty, to create Loch Achonachie. The mass gravity dam is 808 feet (246 m) long and 76 feet (23 m) high. The water level only varies by 2 feet (0.6 m), as the main function of the dam is to regulate compensation water in the river below, but discharges are fed through Torr Achilty power station, which can generate up to 15MW.^[35]

Third phase

The third stage of the project was to modify the River Orrin, which drops by some 700 feet (210 m) in the 6 miles (9.7 km) above its junction with the Conon. A mass gravity dam was constructed 8 miles (13 km) from the junction, which was 1,025 feet (312 m) long and 167 feet (51 m) high. The resulting reservoir is nearly 5 miles (8 km) long. Because the water level is around 135 feet (41 m) higher than it was when it was just a river, a second dam had to be built to prevent water flowing down a branch in the valley. This is an earth dam with a concrete core, of a similar length to the main dam. Over 3 miles (4.8 km) of tunnel and a steel pipeline deliver the water to Orrin power station on the southern shore of Loch Achonachie. This phase cost £2.8 million, of which a substantial amount was needed to ensure that fishing could continue in the valley.^[36]

Because of the large changes in the surface level of the reservoir, the only type of fish pass that was acceptable to the fishing interests was a Borland fish pass. This is similar to a navigation lock, with an upper and lower pool, connected by a sloping shaft. Water flowing out of the lower pool attracts migrating fish such as salmon, and a sluice gate then closes so that the shaft fills, enabling the fish to reach the upper pool and to proceed upstream. Juvenile smolts can enter the upper pool and slither down the shaft when leaving the spawning grounds. A Borland fish pass can accommodate changes in the upper surface level of 20 feet (6.1 m), but because the level of the Orrin Reservoir varies by much more than this, four fish passes were built. Similar fish passes were also installed at Torr Achilty, Luichart, Meig and Achanalt dams, and whereas fish had previously been unable to access the Conon above Conon Falls, the fish passes opened up some 20 miles (32 km) of river to them, as far upstream as Achnasheen. As part of the project, 200,000 salmon fry were released into the Upper River Bran.^[37]

Private schemes

At Dunglass Island, a weir at the upstream end controls the flow of water along the western side of the island, and there is a second weir half way along the eastern channel.^[38] During 2015, two Achimedes screw turbines were installed at the upstream weir, to provide power for the Brahan estate. The turbines produce a maximum of 100 kW, and energy not used by the estate is sold to the National Grid. The turbines, which were commissioned in October 2015,^[39] are designed to work with a head of just 5 feet (1.5 m). Because the level of the river fluctuates by up to 2.3 feet (0.7 m) as a result of discharges from the older hydro-electric schemes further up the river, the screws are set at different heights, to ensure the water is used efficiently whatever the river level.^[40]