Why Arc Hydro for groundwater?
Freshwater is one of the earth’s most precious resources, vital to
human life and to plant and animal life. The volume of groundwater is much larger
than the volume of water in rivers and lakes, but it lies hidden beneath the land surface
in aquifers. About 90 percent of the earth’s readily available freshwater is stored as
groundwater, slowly percolating through the pore spaces and fractures of rocks near
the earth’s surface. Large regions of the world depend on groundwater for their water
supply, particularly in rural areas, because aquifers are spatially extensive.
Groundwater has not been a traditional area of application of geographic information
systems (GIS) to water resources, in part because groundwater resources are less visible
and readily mapped compared to streams, rivers, lakes, and watersheds. Also, groundwater
is inherently a 3D phenomenon because the depth at which water is found in a well
is a critical measure of its accessibility. As a well is drilled, its borehole passes through
many subsurface strata laid down in layers over geologic time. The spatial extent of these
layers is much larger than is their vertical thickness, much like sheets of paper, so 2D
GIS mapping of well locations and aquifer boundaries is the normal point of departure
for groundwater projects. The core framework of the Arc Hydro data model supports
2D mapping of groundwater resources, and the extensions of this model support 3D
representations of boreholes and hydrogeologic strata.