AP_环境科学_Environmental Science - A Global Concern (10th Edition)-321-360.pdfVIP

reconstructed is shown in figure 13.32b. They narrowed the Stabilizing banks is an important step in stream restoration. channel with large stone blocks, which also provide a good Where banks have been undercut by erosion and stream action, surface for anglers to walk along the stream. There isn’t much they will continue to be unstable and cave into the stream. Ide- biological production in this stream model, but that isn’t impor- ally, the bank should be recontoured to a slope of no more than tant to many anglers. They expected the Department of Natural 45 degrees ( fig. 13.33). Soil can then be held in place by rocks, Resources to stock the stream with hatchery-raised fish, which planted vegetation, or other ground cover. It may be necessary to usually are caught before they have time to learn to forage for install erosion control fabric or mulch to hold soil until vegetation natural food. is established. If space isn’t available for recontouring, steep Other groups involved in stream restoration objected to the banks may have to be supported by rock walls, riprap, or embed- artificial nature and lack of a native biological community in ded tree trunks. this design. Figure 13.32c, shows an alternative approach that was ultimately adopted for most of the stream. This is the same Severely degraded or polluted sites can be section shown in figure 13.32a. Straw bales were placed in the repaired or reconstructed deepest part of the stream. This narrowed the stream and increased the speed of the current, w