Discharges 



The average annual tile discharge from 1966 through I969 was 

 1.4 acre-feet per acre (ac-ft/ac) from the tiled areas 

 studied. 



Long-term changes in the average tile discharge were not 

 observed during the more intensive investigations. This 

 relatively high discharge figure can possibly be attributed 

 to the fact that there is no way of knowing exactly how many 

 acres are actually drained by a given tile system. Land 

 adjacent to tiled fields or lying upslope some distance 

 from a tiled area is often drained by the tile system. 

 After adjoining fields are tiled, it is expected that the 

 average annual discharge would decrease significantly. 



The average monthly discharge from valley tile systems 

 ranged from O.O5 ac-ft/ac in the winter months (December and 

 January) to 0.2 ac-ft/ac during July. 



Flows from individual tile drains differed widely. Total 

 annual discharge ranged from a low of 0.3 ac-ft/ac to a high 

 of 17.3 ac-ft/ac for tile systems investigated in I968. In 

 1968 it appears that about l4 percent of the tile systems 

 investigated discharged more water than was applied for 

 irrigation, assuming an average application rate of 

 3.0 ac-ft/ac/yr. 



Tile systems in the Byron to Westley area discharged an 

 average of 2.3 ac-ft/ac/yr for a two-year period, which was 

 twice that dischatrged from the Gustine to Mendota area. 

 Discharges from the Westley to Gustine area (O.69 ac-ft/ac/yr) 

 was close to that observed from tile systems in the Tulare 

 Lake area (0.57 ac-ft/ac/yr). 



Although tile discharge varies greatly between tile systems 

 and major tiled areas depending upon soil conditions and 

 irrigation, the average discharge from a large area of 

 drainage systems can be expected to remain rather constant 

 from one year to the next. 



Conclusions 



1. Nutrient (nitrogen and phosphorous) concentrations in 



tile drainage composited from the San Joaquin Valley can 

 be expected to be close to the values previously predic- 

 ted by the Department of Water Resources in Appendix D, 

 Bulletin No. 127, "Waste Water Quality, Treatment, and 

 Disposal", April I969. 



