What is the difference between old canals and modern canals?

Answer 1

Old canals such as those in Peru or Iraq were dug by hand with simple tools. They are narrow compared to modern canals and are not lined with waterproof material like concrete. Their main purpose was to irrigate fields for crops in marginal climate areas .Modern canals often bring in domestic and industrial water from hundreds of Km away ,whereas old canals were often short-2-20km.Modern canals in nations like New Zealand are mainly to redirect natural water courses to use the flow of water for HEP rather than for irrigation eg 80% of the natural water from the Wanganui River which exits to the SW was redirected northwards ,via drop shafts, canals, lakes and tunnels to Lake Taupo. The east and west diversion schemes from both watersheds of the central plateau of the North Island, increased the volume of water into L Taupo by 20%.The samewater runs through 10 HEP stations on its way north to the Tasman sea.

Los Angeles ,a city of 7milion people, is in an area with only 250mm of rainfall annually.Large canals bring in water from snow melt from a branch of the Rocky Mountains far to the North east.