46 



BULLETIN 304, IT. S. DEPARTMENT OF AGRICULTURE. 



Practice is not uniform as to the best method of preventing water 

 from flowing back through the pipes into the district from the river 

 when the pumps are not operating. Some prefer to carry the dis- 



r^ 



W-Pouna 'P/'/es 



pipe 



toncre te Supports 



^Sheet P///>>ff 

 Fl G 2.— Plan and elevation of pumping plant, Louisa-Des Moines Drainage District No. 4, Iowa. 



charge pipe through the levee above high water and then down, with 

 its end opening below low-water lin'e ; so as to secure a water seal. 

 This is necessary in order that the pipe may act as a siphon and that 



