Water and the Hydrogeology of Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 86

FIGURE 3.23
Groundwater flow along topographically generated pres-
sure gradients. (Modified from Heath, R.C., Basic Ground-
Water Hydrology , United States Geological Survey, Water
Supply Paper 2220, United States Government Printing
Office, Alexandria, VA, 1983.)
Actual path of
water molecule
Groundwater
flow direction
Sand grains
FIGURE 3.24
Groundwater flow on the micro
scale.
groundwater to flow upward and reach surface water. The arrows in Figure 3.23 show the
directions of groundwater flow in response to these pressure differentials.
At the microscale within the saturated zone, groundwater does not travel in a straight
line. Figure 3.24 shows one pathway a particle of water may take when moving within the
saturated zone.
3.5.5 Primary Porosity
To reiterate, groundwater travels through the subsurface through the interconnected pores
between the individual minerals grains. Porosity is the percentage of the volume of the
sediment that is open space (pore space) and is depicted in Figure 3.25.
Well-sorted and well-rounded sediments have a higher degree of porosity compared to
poorly sorted sediments, because there are no fine-grained particles to fill the pore space
between the well sorted and rounded grains. Figure 3.25 depicts well-sorted materials and