The Theewaterskloof Dam forms part of the one of the most imaginative water transfer schemes in South Africa which links the Berg and Sonderend rivers in the Western Cape. A provisional dam design had actually been completed by 1952, and by 1964 the focus has zoomed in on the Theewaterskloof as the best storage site available. The scheme essentially involved linking the two water-rich catchments of the Riviersonderend and the Berg River to discharge surplus winter runoff into one central storage dam. The Franschhoek Tunnel is a reinforced concrete tunnel runing from the Charmaine outlet through the Theewaterskloof basin. The 4,3 m-diameter tunnel penetrates the Franschhoek Mountains for a distance of 7,9 km and breaks through at Assegaaibos in the Berg River Valley. Ground conditions were found to be exceptionally bad in some places, with geological formations varying tremendously from hard to soft, sandy conditions.