ISMSE Alternative Nourishment Strategy

The long-term resiliency of this shared Cape Cod Bay shoreline is largely dependent on the ability of the longshore sediment transport system to supply sand to coastal wetlands. Since the mid-20th century, approximately 25% of this shoreline has been armored to protect upland properties from erosion, alterations that, in the absence of mitigation, have altered wave and sediment transport processes, reducing the natural source of sand available to the shoreline. Traditionally, property owners seeking Conservation Commission approvals for CES construction are required to nourish annually on a parcel-by-parcel basis with volumes estimated to offset associated reductions in sand supply. Although ensuring that sand is supplied to the nearshore environment, the effectiveness and efficiency of individual parcel-based approaches, however, can be limited by operational challenges such as physical and legal access or time of year restrictions; management challenges associated with organizing, coordinating, supervising, and enforcing nourishment activities; and volume estimates based on average erosion rates that can be more characteristic of a continuous process than an episodic event contributing to misperceptions of the year to year need for sand replenishment. The effectiveness of parcel-based mitigation often varies based on its location within the littoral cell or the nature and extent of adjacent shoreline structures. This dataset summarizes recommendations for an alternative regional shoreline-based approach to annual nourishment that can be implemented under the present state and local regulatory framework to increase mitigation effectiveness and efficiency. The characteristics that make shorelines resilient and their ability to respond to natural hazards operate independently of municipal boundaries. To facilitate and promote consistent and synergistic management techniques shoreline characteristics of three adjacent communities were examined in the absence of municipal boundaries in order to develop a comprehensive shoreline management framework. The three adjacent communities, Brewster, Dennis and Orleans, partnered to develop a framework for an intermunicipal approach to shoreline management to promote short- and long-term science-based decisions that will maximize the effectiveness and efficiency of community responses to the increased threat of coastal hazards. GIS-based datasets comprising the Intermunicipal Shoreline Management Database were compiled from existing sources and supplemented by additional data where appropriate. Contemporary shoreline resilience conditions have been characterized throughout the study area to identify issues and challenges currently confronting each town’s management efforts. This assessment is based on existing data (available through CZM’s Shoreline Change database, MORIS and MassGIS), information from multiple MCZM Coastal Resiliency projects (Borrelli et al., 2016; Borrelli et al., 2017; Giese et al., 2013, Giese et al., 2018) and other resources including the U.S. Army Corps of Engineers, the U.S. Geological Survey, NOAA, the Barnstable County Dredge Program, and records from the individual towns.这片共享科德角湾（Cape Cod Bay）岸线的长期韧性，在很大程度上取决于沿岸输沙系统（longshore sediment transport system）为滨海湿地（coastal wetlands）供给泥沙的能力。自20世纪中期以来，该岸线约25%的区域已实施护岸加固措施，以保护高地地产免受侵蚀。若不采取缓解措施，这类改造会改变波浪与泥沙输运过程，削减岸线可获取的天然沙源。 传统上，申请保护委员会（Conservation Commission）批准开展CES（海岸侵蚀防护结构，Coastal Erosion Structures）建设的地产所有者，需按逐地块的方式每年开展泥沙补给，补给量经估算后用于抵消泥沙供给的相关削减量。尽管这类做法可确保泥沙被输送至近岸海域（nearshore environment），但逐地块实施模式的有效性与效率仍受多方面限制：实操层面的挑战，如物理与法律准入限制、季节约束；组织、协调、监管及落实补沙活动相关的管理难题；以及基于平均侵蚀速率的量估算——这类速率更偏向连续过程的特征，而非偶发事件的规律，易导致对年度补沙需求的认知偏差。 逐地块减灾措施的有效性，通常会因其在沿岸输沙单元（littoral cell）中的位置，或相邻岸线防护结构的性质与范围而有所差异。本数据集总结了一种替代方案的相关建议，即采用基于区域岸线的年度补沙模式，该模式可在当前州级与地方监管框架下实施，以提升减灾措施的有效性与效率。 决定岸线韧性的特征及其应对自然灾害的能力，不受行政辖区边界的限制。为推动形成统一且协同的岸线管理技术手段，本研究打破行政辖区边界限制，对三个相邻社区的岸线特征展开调研，以构建综合性岸线管理框架。 这三个相邻社区——布鲁斯特（Brewster）、丹尼斯（Dennis）与奥尔良（Orleans）——携手合作，构建跨市政岸线管理框架，以推动制定短期与长期的科学决策，最大化社区应对日益严峻的海岸灾害威胁时的响应效率与效果。 本数据集所包含的跨市政岸线管理数据库，基于地理信息系统（GIS, Geographic Information System）技术，由现有资料汇编而成，并在适宜场景下补充了额外数据。 本研究对整个调研区域内的当前岸线韧性状况进行了特征梳理，以明确各城镇管理工作当前面临的问题与挑战。本次评估基于现有数据（可通过CZM岸线变化数据库、MORIS与MassGIS获取）、多项MCZM海岸韧性项目的相关资料（Borrelli et al., 2016; Borrelli et al., 2017; Giese et al., 2013; Giese et al., 2018），以及其他来源信息，包括美国陆军工程兵团（U.S. Army Corps of Engineers）、美国地质调查局（U.S. Geological Survey）、美国国家海洋和大气管理局（NOAA, National Oceanic and Atmospheric Administration）、巴恩斯特布尔县疏浚项目，以及各城镇的存档记录。