LAYING OUT A DRAIN OR SYSTEM 



111 



respects it is desirable that the laterals lie at angles less 

 than 90 to the main: (1) with an angle less than 90, 

 it is not necessary to introduce a curve or angle at the 

 outlet end of the lateral ; (2) in very many cases the 

 outlet of the area to be drained is other than square, 

 and can be more economically served by the lateral if 

 it lies at an angle less than 90 degrees to the main. 



When two laterals, entering the main at an interval of 

 100 feet, lie at an angle of 30 degrees to the main, they 

 are just 50 feet apart. If two laterals, entering the main 

 100 feet apart, lie at an angle of 60 degrees to the main, 

 their distance apart is nearly 86 feet, 7 inches. If two 

 laterals, entering a main 100 feet apart, lie at an angle of 

 45 degrees, the distance between them is nearly 70 feet, 

 8 inches. (See Fig. 44, also Table XL) 



TABLE XI 



RELATION OP ANGLE OF APPROACH TO MAIN TO DISTANCE BETWEEN 

 LATERALS, WHEN LATERALS ENTER MAIN 100 FT. APART 



