Abstract or Summary
The costs and the effectiveness of five recently constructed living shoreline projects in New Jersey were evaluated. The projects selected are representative of the diversity of the project types found in New Jersey. They range in size from large to small, from simple to complex, and from relatively inexpensive to costly. At several sites, cost information was also obtained for nearby conventional gray shoreline treatments. This allowed for a qualitative comparison between green and gray alternatives. The cost information for each project was provided by organizations involved in their funding, design, and construction. The level of detail provided varied significantly. All provided costs were compiled and grouped into categories for analysis and comparison. It should be noted that not all of the cost estimates included enough detail for a complete cost breakdown, therefore the results need to be interpreted cautiously.
The total cost for the five living shoreline projects in the study ranged from $88 per linear foot to $2,018 per linear foot. The five conventional alternatives ranged in cost from $462 per linear foot to $3,448 per linear foot. In general, the smallest, least complex project of each type was the least expensive, and the largest, most complex project was the most expensive. Overall, design and permitting costs, maintenance and adaptive management costs and monitoring costs were higher for the living shoreline projects than for conventional projects; however, construction costs for the living shoreline projects were generally lower. Some of the living shorelines projects were constructed either partially or wholly with volunteer labor which helped reduce costs.
In terms of the distribution of the costs associated with each project type, significant differences were found. For the living shoreline projects, materials and labor made up a wide range (34.5% to 91.8%) of the total project costs. For the conventional projects, materials and labor consistently made up the largest proportion (88.9% to 98.6%) of the total cost. The split between materials and labor was different as well; construction costs were more evenly split between materials and labor for the living shoreline projects, while they were more heavily weighted towards material costs for the conventional projects. Design and permitting, monitoring, maintenance, and adaptive management costs, all made up a greater proportion of the cost of the living shoreline projects. This is driven in part by the relative inexperience with living shoreline projects within the state that often increases the permitting and monitoring costs, and in part by the way in which maintenance and adaptive management is viewed/interpreted. For living shoreline projects, maintenance and adaptive management is often considered up front, as a part of the initial planning process and the collected cost information reflects that; whereas for conventional projects, maintenance and adaptive management are often considered separate projects entirely and therefore these costs are not contained in the information provided. For some of the living shoreline projects, the non-construction costs were found to be more than double the construction costs.
The long-term costs of all the projects were estimated using a framework developed as a part of the Hudson River Sustainable Shorelines Project (HRSSP). The framework was chosen because of its adaptability, including the ability to modify and add new cost categories. The framework requires a set of assumptions related to interest and discount rates, sea level rise, damage potential, and maintenance including replacement. One of the main conclusions from the long-term cost analysis was that the costs of the living shoreline projects are more evenly distributed through time, while the costs for the conventional shoreline stabilization approaches are more concentrated. The major costs associated with all of the conventional structures were associated with initial construction costs and replacement costs, while the living shoreline projects were more influenced by maintenance, monitoring, adaptive management, and damage costs.
The effectiveness of the living shoreline projects was evaluated by analyzing and comparing pre- and post construction shoreline changes and comparing them to a nearby control site. Overall, three of the five living shoreline projects (Berkeley Island, Gandys Beach, and Matts Landing) were found to be clearly effective at stabilizing the shoreline in their respective project areas, and in some cases even promote shoreline advancement (Gandys Beach and Matts Landing). The results of the shoreline stability analysis at the other two sites are less obvious due to the lack of high-quality historical imagery prior to project installation. These two sites exhibited the lowest pre-construction rates of shoreline change and standard deviations of 40 to 65% of their annual rate of shoreline change post-construction.
A second measure of effectiveness was evaluated for the three living shoreline projects that contain feature wave dissipation structures (Gardner’s Basin, Gandys Beach, and Berkeley Island). For these projects, waves were measured offshore and inshore of the wave dissipation elements, and wave attenuation was calculated. All three projects were found to be effectively attenuating waves. At Gardner’s Basin, the majority of wave heights were reduced by 50% or more, while wave heights at Berkeley Island were reduced between 25% and 75%. At Gandys Beach, the wave attenuation was more variable, due to the complexity of the hydrodynamic conditions at the site; however, attenuation of between 0% and 50% was most common.
The effectiveness of the gray alternatives was not evaluated as a part of this study because comparing the results to the living shoreline projects could result in misleading conclusions. While bulkheads and revetments are generally very effective at maintaining the shoreline (particularly when newly constructed), the length of the study precludes consideration of some of the other long-term, effects which need to be considered if their effectiveness is to be directly compared to living shoreline projects.
Overall, some of the key takeaways from the analysis of the cost and effectiveness data for the five living shoreline and five conventional shoreline stabilization projects were: 1. Costs for both living shoreline and conventional shoreline stabilization projects were found to vary widely; however, the living shoreline project costs were generally lower. 2. The distribution of costs for living shoreline and conventional shoreline projects were found to be different, with design and permitting, monitoring, maintenance, and adaptive management costs making up a larger proportion of the living shoreline project costs. 3. The long-term cost of living shoreline projects was determined to be more evenly spread over time, while the costs of conventional projects were concentrated at discrete times representing initial construction and replacement. 4. Three of the five living shoreline projects were found to be effective in reducing erosion compared to a nearby control. 5. All three living shoreline projects containing wave-attenuating structures effectively attenuated waves although the degree of attenuation was found to vary