Describe how water can be stored beneath the ground surface. Explain why the stores and flows of groundwater can vary in time and space within a drainage basin.

Water is stored beneath the ground surface at different levels. Closest to the surface would be

water that exists as soil moisture when water which hit the ground surface infiltrates into the

ground and the regolith, which is a collection of loose particles that have been weathered from

the bedrock. The water seeps into the wider pore spaces between these soil particles and thus

this top layer holds most moisture per unit space. At the deeper level, water percolates into

the join spaces that exists within the bed rocks and saturate any spaces available. The amount

of water held in the deep ground is dependent on the permeability of the bedrock material.

Stores and flows of groundwater varies in time within the drainage basin as a result of storms

(short moment) and seasonality (longer period). As climatic factors alter the input into the

drainage basin via precipitation, the stores and flows of groundwater varies according to these

inputs. A sudden storm would provide a huge supply of water to the ground, leading to a

recharge of the stores of groundwater and filling it up. The rising water table as a result of this

input would raise the local water pressure and increase the groundwater flow into channels or

towards other areas of the ground with lower pressure (albeit rather slowly). On the other

hand, a dry season, or prolonged deficient in precipitation would deplete the stores of

groundwater and thus reduce the groundwater flow within the drainage basin. This depletion

could be exacerbated by the presence of human settlements as the dry season meant that they

would rely on groundwater stores more intensively (having dried up surface stores).

Spatial variation in stores and flows of groundwater is a natural outcome of the varying geology

of the drainage basin in space. As the permeability of the bedrock material determines the

capacity of the ground, the parts of the drainage basin dominated by rather impermeable

bedrock like shale (an aquiclude) would have lower stores and less groundwater flows relative

to the area of the drainage basin with a limestone bedrock (an aquifer). In an area with a

mixture of aquifer and aquiclude, the positions of these rocks would impact on the flow of the

groundwater. For example, an overlying aquiclude on an aquifer would apply pressure on the

water in the aquifer, possibly leading to more rapid groundwater flows.