Groundwater is strongly related with surface
water in the Edwards Aquifer. Water seeping
through the limestone rock of the aquifer has created
a karst landscape with many caves, fractures,
and sinkholes that allow fast movement of water
from the surface into the aquifer formation and
within the subsurface (figure 1.4).
The groundwater discharge from the San
Marcos Springs forms the flow of the San Marcos
River. As this river meanders downstream, it is
joined by the Blanco River, whose flow is derived
mostly from surface runoff, and these in turn are
tributaries of the Guadalupe River, which carries
their waters to the Gulf of Mexico. Normally a
quiet, slow-moving river, the Guadalupe can turn
into a raging torrent during severe storms and
devastate the surrounding countryside.
To accurately describe the water resources of
the region, we must map both groundwater and
surface water features together (figure 1.5) and
define the relationships between them. This is part
of the new design of Arc Hydro, which includes
a framework data model with basic surface water
and groundwater features and additional components
describing unique aspects of surface water
and groundwater.