Hundreds of feet installed per day with a crew of 2 laborers. 2 skilled carpenters average 50 feet per day. Simple wood supports used for holding sections to grade. Requires sturdy and complex wooden form work. Standard radius bottom improves hydraulic flow.
Square bottom creates turblence and deposits.
Forms can be left in for jobsite safety. Open pits are hazardous and collect jobsite debris. Three separate sources for materials create risk of dimensional inaccuracies.