In 1924, workers noticed that the hillside towards Yewtrees Lane, north of the Broomhead site, began slipping as an important overflow channel was being dug. “They realised they needed to do something,” says Mike. “They were digging the channel and the ground kept coming towards them.” A trench was dug in short lengths and a drain up to 50 feet deep was put in, filled with rubble. “That, together with removing 400,000 cubic yards of soil from the top end of the slip, seemed to stop the movement,” Mike says.<\/em><\/p>\n<\/div>\n This Google Earth image shows the Broomhead reservoir.\u00a0 The slope that caused the problems is the forested area on the far side of the lake:-<\/p>\n Google Earth image of the Broomhead reservoir<\/p><\/div>\n .<\/p>\n The problems at this site are documented in some detail in a paper that was published in the Journal of the Institution of Civil Engineers<\/em><\/a> (Beldelow 1944<\/a>).\u00a0 This paper names the landslide the “Waldershelf Slip”.\u00a0 The article documents two phases of movement, with the first starting in 1924 during the construction of the overflow works (which can be seen in the image above).\u00a0 Beldelow (1944)<\/a> includes the following cross section through the site – the slip can be seen on the right side of the diagram, with the inferred slip plane.\u00a0 Note the location in relation to the level of the top of the embankment:-<\/p>\n Cross section through the Broomhead Reservoir, showing the landslide on the right hand side. Diagram from Bendelow (1944)<\/a>.<\/p><\/div>\n .<\/p>\n To stabilise the landslide, the engineers constructed a drain to extract water from the landslide and they removed about 300,000 m\u00b3 of material from the upper part of the slope to reduce the driving load.\u00a0 This work was completed in 1928, and Bendelow (1944)<\/a> reports that the works appeared at first to have been successful.<\/p>\n However, in April 1930 further movement was observed on the slope, including cracks through the overflow weir.\u00a0 A very detailed investigation was undertaken of the causes of the instability, including trial pits dug to a depth of up to almost 30 metres! These found evidence of slip planes through the bedrock, indicating that the slope consisted of an ancient landslide that had been reactivated by the construction of the dam and associated structures.<\/p>\n To stabilise the slope, the engineers removed a further 125,000 m\u00b3 of material, installed drains within the landslide mass, and constructed drains beyond the margins of the landslide to stop water from entering the unstable part of the slope.<\/p>\n To the huge credit of the engineers, these measures proved to be entirely successful, and 75 years after the paper was published the reservoir remains in use.<\/p>\n![\"Broomhead](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2019\/09\/19_09-Broomhead-1-e1568267830373.jpg\")
![\"Broomhead](\"https:\/\/blogs.agu.org\/landslideblog\/files\/2019\/09\/19_09-Broomhead-2-e1568268384881.jpg\")
Reference<\/h4>\n