What is the recommended minimum furrow grade (slope) required to assure proper surface drainage in agricultural fields?

Determine the design discharge at the outlet of a canal, the culturable command area of which is 1000 hectares. The cropping intensities of sugarcane and wheat are 30% and 40%, respectively. The duties of each crop at the head of the canal are 850 hectares/cumec and 1500 hectares/cumec, respectively.

In a tile drainage system, the height of the water table above the impervious layer is 9 m, the depth of the impervious stratum below the center of drains is 8 m, and the permeability coefficient is 0.001 cm/s. The total discharge per unit length carried by the drain is q = 0.75 S8.64 × 106 m3/s/m. Calculate the spacing (S) of the tile drain.