The relationship between porosity $(\eta)$, specific yield $(S_y)$ and specific retention $(S_\tau)$ of an unconfined aquifer is:

1. $S_y+S_\tau = \eta$
2. $S_y+ \eta = S_\tau$
3. $S_\tau+ \eta = S_y$
4. $S_y+ S_\tau + \eta =1$