284 Gathering the pieces
Figure 11.1Donut model variations representing major structural and functional
differences among urban regions. Straight line within urban region is a major river
and line on edge of region is a seacoast.particular value in maintaining a relatively clean river. That enhances nearby
recreation/tourism opportunity and sometimes water supply. Natural vegetation
across the downriver land can provide clean water that dilutes and helps clean
the polluted riverwater.
Fish moving along the river are typically blocked by severe water pollution
downriver of, or in, the metro area. Yet if riverwater is clean enough, fish