VI. A. 4. Management Recommendations |
A broad array of habitat protection and mitigation techniques can minimize or limit the impact of shoreline modifications to estuarine and nearshore marine areas (Williams and Thom 2001). Actions that can mitigate these impacts include avoidance (i.e., no shoreline modification), minimization of impacts by using alternative structural modification strategies, land-use management, and compensation via restoration of other degraded sites. Downing (1983) summarizes some of the advantages and disadvantages of various approaches not only to the property owner, but also to local beach conditions and the nearshore ecosystem (Table VI-3).
Table VI-2. Summary of the Advantages and Disadvantages of Various Shore Protection Alternatives (from Downing 1983).
In general, soft structures are believed to result in less long-term and fewer cumulative impacts to the nearshore ecosystem than do hard structures. However, beach nourishment should be used with caution because the relatively limited amount of regional study devoted to this approach. For example, nourishment does not address the underlying cause of erosion and should be undertaken with an ongoing commitment for periodic maintenance (Shipman 1998). In some cases, homogeneous gravel mixtures may provide few of the intended ecological benefits in some intertidal habitats, resulting in steepened beach slopes (Downing 1983), little moisture retention when drained, and instability under minor wave action. In these cases, beaches may not support desired infauna or epibiota, primary production, or appropriate surf smelt spawning habitat (Williams and Thom 2001).
Some soft structures, such as placement of large woody debris, may enhance the ecological functions provided by the shoreline. Again, the appropriate placement of large woody debris needs more study and should be used with caution. Under extreme tide and wave conditions wood may become unstable and cause damage to property (Williams and Thom 2001).
Revegetation has shown in several cases to improve biological productivity and enhance nearshore conditions (Zelo and Shipman 2000). Dune grass and berm vegetation can greatly increase the resilience of beaches to storm waves. Riparian vegetation is also a key element of shoreline ecological function and has a significant influence on habitat value, both in the riparian zone itself, and in adjacent aquatic and terrestrial areas. Marine riparian zones serve many of the same beneficial functions as freshwater systems (Naiman et al. 1992), while likely providing additional functions unique to nearshore systems (Brennan and Culverwell in prep).
A preferred alternative is to follow guidelines for building setbacks, which is the process of constructing sensitive shoreline structures (i.e., homes) a safe distance from eroding shorelines or bluffs (Terich 1987). Setbacks are considered the safest and least expensive alternative to avoiding hazards along Washington’s erosive coastlines (Terich 1987; Downing 1983; Komar 1998b).
Management of upland groundwater and vegetation also provides a preferred approach that minimizes the need for shoreline stabilization structures. Surface and groundwater management can reduce erosion around sensitive shoreline structures and property (Myers 1996). Water is one of the most common agents of slope instability and erosion, and water supplementation should be kept to a minimum on erosion-prone hillsides and slopes (Myers 1993). Upland and riparian vegetation management should strive to maintain buffers of native vegetation, which may encompass planting of deep-rooted upland vegetation to increase soil stability and reduce erosive hydrologic forces on shorelines (Manashe 1993).
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