FIGURE 1-4 Idealized view of an alluvial river corridor showing the longitudinal (upstream–downstream), vertical (interstitial), and lateral (floodplain) dimensions that interact both hydrologically and ecologically. The riparian area includes the channel system, its floodplain, and the transition zone into the uplands. An alluvial aquifer underlies the channel and includes both a hyporheic zone and a deeper phreatic zone of groundwater. The phreatic zone contains groundwater that has had no contact or mixing from surface sources for very long time periods, often hundreds of years or longer. In contrast, in the hyporheic zone river water moves rapidly (on the order of days) through surficial alluvia characterized by very high hydraulic conductance. Other terms (parafluvial and bank-full) and interactions are described in detail in Chapter 2. pb = point bar. SOURCE: Adapted from Stanford (1998).
DISTINGUISHING RIPARIAN AREAS FROM OTHER AREAS
Another way of characterizing riparian areas is to identify what they are not and to contrast them with other adjacent land and water units. The definition in the preceding section describes riparian areas as “zones of influence” between aquatic and terrestrial areas. As such, riparian areas encompass some or all of the wetlands in a typical landscape setting, but they also include portions of adjacent aquatic and upland environments. Figure 1-5(A) shows a “generic” riparian zone of influence in detail; Figures 1-5(B–E) illustrate this zone of influence in small stream, river, lake, and estuarine-marine settings and approximate the scale at which the zone applies.