<math>Drain\ spacing=\sqrt{\frac{8K_{soil}\left(D_{i}-D_{d}\right)\left(D_{d}-D_{w}\right)+4K_{soil}\left(D_{d}-D_{w}\right)^{2}}{q}}</math> | <math>Drain\ spacing=\sqrt{\frac{8K_{soil}\left(D_{i}-D_{d}\right)\left(D_{d}-D_{w}\right)+4K_{soil}\left(D_{d}-D_{w}\right)^{2}}{q}}</math> |