Freshwater and marine coast ecology 95Figure 4.3Upper streams and lower river with associated wetlands. All three types
of water bodies are typically connected to the underlying groundwater, and have
quite different structure, functions, and protection requirements. The river has been
straightened (channelized) and rocks line the riverbank. Also a bridge and nearby
built structures have fixed the channel in position, reducing its natural capacity to
migrate back and forth in its floodplain. First- to fourth-order streams in the hills,
recreation in a wetland and river floodplain, and agricultural runoff issues in
cropfields are illustrated. Adapted from Taco I. Matthews’ drawing (Forman 2004a).supports many rare species of conservation importance, yet is often degraded by
urban activities.
These river patterns are modified by a cascade of typical urban-region
attributes, including: widespread built areas; impermeable surfaces on
slopes; high peak flows from piped/channelized stormwater; extensive squeez-
ing/straightening/piping of tributaries (and river); major infrastructure conduits
along a river; small maintainance roads crisscrossing floodplains; elimination
of most wetlands; limited natural vegetation remaining across the land; very lit-
tle stream--corridor vegetation; lowered water tables; human wastewater, some
or most untreated, from a concentrated population; numerous old and new
industries; very high road density; huge traffic flows; and much more. These
commonly result in: normal low-water flows; periodic big floods with structural
damage; waste removal and cleaner cities; heavily polluted downriver flows;