The Role of Large Wood in Promoting Channel-Floodplain Connectivity for River Restoration

大木材在促进河道-洪泛区连通性和河流恢复中的作用

• 批准号: 2229839
• 负责人: Ellen Wohl
• 金额: $ 40.29万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-01 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2229839&HistoricalAwards=false
• 关键词: Role; Large; Wood; Promoting; Channel

River restoration has initially focused on channel morphology and subsequently gradually expanded to include reconnection of channels and floodplains. Although stream ecologists have recognized the critical ecological role of floodplains for decades, and hydrological, geomorphic, and biogeochemical research now increasingly emphasizes the importance of floodplains, floodplains do not receive the legal protection of navigable water and have been extensively altered throughout the US. Consequently, one of the issues now at the forefront of river management and restoration is how to effectively re-connect altered channels and floodplains. Reconnection requires multiple changes of differing importance in specific settings. Large wood (LW) reintroduction or retention falls within this scope, but guidelines have not been developed regarding how much LW to reintroduce, in what configuration, and where. This research will address an important gap in knowledge regarding the quantitative impacts of LW jams on channel-floodplain hydrologic connectivity and how these impacts can inform river restoration design. Large wood can be a dominant driver of channel and floodplain complexity. LW can alter the local distribution of hydraulic forces, sediment dynamics, hyporheic exchange flows, channel cross-sectional and planform geometry, and channel-floodplain connectivity. These effects operate in a nonlinear fashion as accumulations of LW in a logjam and in progressively larger and more closely spaced logjams create emergent patterns in these response variables. However, thresholds can not yet be predicted for the magnitude of change in response variables with respect to LW quantity or spatial distribution. This is important in the context of river restoration, which reintroduces LW in channels despite inability to predict hydraulic, geomorphic, or ecological responses. This knowledge gap of quantitatively predicting the physical effects of LW on channel-floodplain hydrologic connectivity will be addressed by by (i) measuring LW and associated connectivity in diverse field settings; (ii) assessing threshold responses in connectivity due to river morphologic and LW characteristics; and (iii) developing guidelines for representing LW characteristics and associated hydraulic responses in numerical models. In this context, the project defines channel-floodplain hydrologic connectivity as being present when flow overtops the morphological channel banks and spreads onto the adjacent floodplain. The project objectives are to: (1) collect data from natural channels on LW jam characteristics and associated influences on channel-floodplain connectivity; (2) use these data to develop guidelines for calibrating LW characteristics and hydraulic responses in numerical hydraulic models; and (3) co-generate knowledge and best practices with river restoration practitioners for long-term monitoring of LW jam benefits. The project will integrate new knowledge of how LW jams influence channel-floodplain interactions with ongoing and future investments in river restoration projects, and planned activities are aimed to advance the sustainability of river restoration design, promote restoration monitoring and citizen-science learning to diverse stakeholders and restoration practitioners, and improve STEM education focused on sustainable and resilient natural systems. This award is co-funded by the Environmental Sustainability program in CBET/ENG and the Hydologic Sciences program in EAR/GEO.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

河流恢复最初侧重于河道形态，随后逐渐扩展到包括河道和洪泛区的重新连接。尽管几十年来溪流生态学家已经认识到洪泛区的重要生态作用，并且水文、地貌和生物地球化学研究现在越来越强调洪泛区的重要性，但洪泛区并没有受到通航水域的法律保护，并且在美国各地已经发生了广泛的改变。因此，目前河流管理和恢复的前沿问题之一是如何有效地重新连接改变的河道和洪泛区。重新连接需要在特定设置中进行多次不同重要性的更改。大型木材 (LW) 重新引入或保留属于此范围，但尚未制定关于重新引入多少 LW、以何种配置以及在何处重新引入的指南。这项研究将解决关于 LW 堵塞对河道-洪泛区水文连通性的定量影响以及这些影响如何为河流恢复设计提供信息的重要知识空白。大木材可能是河道和洪泛区复杂性的主要驱动因素。 LW 可以改变水力的局部分布、沉积物动力学、潜流交换流、河道横截面和平面几何形状以及河道-洪泛区的连通性。这些效应以非线性方式运作，因为 LW 在僵局中以及逐渐更大且间隔更紧密的僵局中累积，在这些响应变量中创建了新的模式。然而，还无法预测响应变量相对于 LW 数量或空间分布的变化幅度的阈值。这在河流恢复的背景下非常重要，尽管无法预测水力、地貌或生态响应，但河流恢复仍会在河道中重新引入 LW。定量预测 LW 对河道-洪泛区水文连通性的物理影响的知识差距将通过以下方式解决：(i) 测量不同现场环境中的 LW 和相关连通性； (ii) 评估由于河流形态和 LW 特征而导致的连通性阈值响应； (iii) 制定在数值模型中表示 LW 特性和相关水力响应的指南。在这种背景下，该项目将河道-洪泛区水文连通性定义为当水流超过形态河道岸并扩散到邻近的洪泛区时就存在。项目目标是： (1) 从天然河道收集有关 LW 堵塞特征以及对河道-洪泛区连通性的相关影响的数据； (2) 使用这些数据制定校准数值水力模型中的 LW 特性和水力响应的指南； (3) 与河流恢复从业者共同创造知识和最佳实践，以长期监测 LW 堵塞的效益。该项目将把关于 LW 堵塞如何影响河道-洪泛区相互作用的新知识与河流恢复项目的正在进行和未来的投资相结合，计划的活动旨在促进河流恢复设计的可持续性，促进不同利益相关者和恢复从业者的恢复监测和公民科学学习，并改善以可持续和有复原力的自然系统为重点的 STEM 教育。该奖项由 CBET/ENG 的环境可持续发展计划和 EAR/GEO 的水学科学计划共同资助。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。