Table 1: Details of Sauda-Snna underground construction Project element Tunnel length (m) Tunnel section (m2) Excavation volume (m3) Comments Snna H Headrace tunnel 11,225 52 Tailrace tunnel 1250 90 Common to Snna L Access tunnels 1050 + 370 30 + 22 Common to Snna L Transfer tunnels 4188 + 8140 18.5 + 9.6 Intake shaft 1060 Power station cavern 51,500 Common to Snna L (two units of three) Surge shaft 550 10-30 Snna L Headrace tunnel None Tailrace tunnel 1250 90 Common to Snna H Access tunnels 1050 40 Common to Snna H Pressure shaft 280 14 Transfer tunnels None Intake shaft None Power station cavern 51,500 Common to Snna H (one unit of three) Surge shaft None