Water, water, everywhere...

Well duh, it's an island. Maui's humid tropical climate and diverse terrain set the stage for some incredible hydrological features! Ground water, water which moves in the porous space between rocks, is one of Maui's most important resources because it is used for agriculture, drinking, and other industrial needs.

The majority of rainfall returns to the ocean via streams or the atmosphere by evaporation, but some remains trapped in the earth. Beneath the surface, water stays in either the saturated or unsaturated zone. In the unsaturated layer, water and air are caught between the pore spaces in rocks; in contrast the saturated layer contains only water and is refereed to as the water table.

The amount of water Maui's volcanic soil can hold, or its permeability, varies based primarily on the viscosity of the the lava flow and topography. More compact flows which occur as incline decreases generally hold less water resulting in surface water.

Pipiwai Trail

Surface water occurs where the amount of water flow exceeds the ground's ability to absorb it and generally takes the form of streams and ponds. Components of surface water include direct runoff, base flow (where streams meet the water table), excess irrigation, and water returned from bank storage. Streams in Maui can be effluent, meaning the water table facilitates stream flow, or influent meaning they lose water to recharge the aquifer.

Recharge, or the replacement of water reserves in the ground, is particularly important because Maui contains no desalination plants. Recharge occurs as precipitation, runoff, and surface water makes its way to aquifers, the last permeable layer of soil from which water can still be obtained. Aquifers can be unconstrained like the water table, or constrained as in trapped between two impermeable layers such as an artesian aquifer.