Groundwater is water located below the ground surface in the spaces between soil particles (the soil pore spaces) and rock fractures in bedrock.  In nature, surface water and groundwater are intimately connected via the water cycle.  Surface water, flowing or stagnant, percolates downward through the soil and becomes part of the groundwater table.  The groundwater then either becomes stored (temporarily or permanently) or flows down-gradient and is often forced to resurface in areas such as springs, seeps, river beds, lake bottoms, and wetlands.

Flowing to the Surface

Areas where groundwater comes to the surface or is very close to the surface usually form wetlands and are some of the most biologically diverse areas on the planet. Groundwater is shallow in wetlands, often ponding or saturating the soil at the surface because of an impermeable strata lower in the soil.  It is the existence of this shallow groundwater that makes these areas wetlands.  Hydrophilic plants, macroinvertebrates, and, in turn, larger animals are all supported by this interaction of surface and groundwater.

Temporary Storage

Bank storage is one way that groundwater may be stored.  During spring runoff the level of lakes, ponds, streams and rivers rise due to precipitation or snowmelt, saturating the banks of the waterbody.  This elevates the local groundwater table.  Once the waters subside, the groundwater that saturated the banks is higher than the waterbody.  This stored groundwater then slowly flows back into the waterbody and augments summer low flows.  The process of low-flow augmentation is especially important in streams that are chronically dewatered from agriculture, ranching, or urban use.

Semi-Permanent Storage

If, instead of flowing back to the surface, the groundwater becomes part of an aquifer where it very slowly moves down gradient until somebody removes it or it finds its way back to the surface again.  If there were a disconnection between surface water and groundwater in this case, much of our drinking and irrigation water storage would not be replenished.

There are many ways to disconnect groundwater and surface water, including removing a stream from its floodplain, creating impermeable surfaces, and filling or draining wetlands.  Even though we may not be able to directly see the surface water-groundwater interaction and we depend on groundwater for most of our freshwater needs One should not discount this vital connection, our increasingly precious water resources depend on it.