310 Ground Water, Wells and Farm Drainage. 



In such cases deep open ditches must be provided to co.i 

 vey the water out of the country, serving as outlets foi 

 underdrains laid in the adjoining fields. A district of this 

 type of land drainage is represented in Fig. 130, covering 

 nearly six square miles. The double lines represent deep 

 open ditches and the single lines underdrains. 



Another drainage system of this sort in Mason and 

 Tazwell counties, 111., has 17.5 miles of main ditch 30 to 

 60 feet wide at the top and 8 to 11 feet deep. Leading 

 into these mains there are five laterals 30 feet wide and 7 

 to 9 feet deep, the whole system embracing 70 miles of 

 open ditch for the purpose of providing outlets for under- 

 drains. 



