What would the specific yield of an unconfined aquifer be if the porosity is 0.3 and the effective porosity is 0.18?

To determine the specific yield of an unconfined aquifer, it is important to understand the relationship between porosity and effective porosity. Porosity refers to the total void space in the material, while effective porosity considers only the interconnected pore spaces that contribute to the flow of water.

In this case, the effective porosity is given as 0.18, which directly represents the amount of water that can flow out of the aquifer when under gravity. Since specific yield is essentially synonymous with effective porosity for an unconfined aquifer, this makes the effective porosity value the specific yield.

Therefore, the specific yield of the aquifer is indeed 0.18, as it reflects the amount of water that can be drained under the influence of gravity. Knowing this helps in evaluating the water resource potential of an aquifer, particularly in terms of its capability to sustain withdrawals.