Collaborative Research: Emergent Hydrological Properties Associated with Multiple Channel-Spanning Logjams

在这个建议中，我们希望量化河流形状，堵塞，堵塞周围的水的运动和周围的沉积物之间的关系。 在这样做的过程中，我们将提前了解（一）堵塞如何影响水质和河流社区在森林流域，（二）历史和持续的人类改造的影响，在森林地区的河流走廊，以及（三）如何设计人工堵塞河流管理流温度，营养物质和水生生物群落。我们的工作将与资源管理人员和从业人员分享，以帮助解决与河流管理和恢复相关的问题。学生的参与将包括：（一）K-12学生，通过与小学教师合作编写的课程材料;（二）参与实地数据收集和分析的本科生，包括来自不同背景的学生;及（iii）负责主要数据分析及解释的研究生，谁将有机会与本科生研究人员一起工作，并指导他们。在河流走廊的大型木材（LW）的好处是多方面的，包括提高潜流交换流（HEF）的潜力。现有的工作集中在单根原木或单根堵塞物附近的HEF。然而，在森林地区的天然渠道，人类的改变最少，通常包含丰富的分散LW件和多个木塞不规则地沿沿着通道。我们几乎没有迹象表明，是否多个跨通道的堵塞产生的附加或非线性影响HEF，但这些替代品有重要的意义，了解河流生态系统功能和河流管理和恢复。我们的主要目标是量化HEF如何随着与跨通道堵塞相关的通道异质性的增加而变化。我们将使用现场测量，物理实验和数值模型，以评估与不同的空间密度的通道跨越堵塞HEF的特性。我们预计，堵塞和HEF之间的非线性关系，导致增加床型，如池，最大限度地提高通量率，增加水头梯度与堵塞引起的回水之间的下游间距减少，和更厚的沉积砂和砾石，共同作用，以创建陡峭的水力水头梯度内厚，渗透性床序列。我们还预计，在过渡到anabranching作为增强的HEF之间的分割通道的结果，堵塞和HEF之间的非线性关系。 这项工作的影响将与工程堵塞，这是目前正在添加到河流，但没有系统的了解如何影响LW添加规模与河流的大小，木材的体积和空间分布，或木材和通道的特性，限制我们的能力，设计LW为基础的河流恢复，以达到所需的HEF水平。 作为我们研究的一部分，我们将为当地的K-12学校开发课程。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this proposal we look to quantify relationships among river shapes, logjams, and the movement of water around jams and through surrounding sediments. In doing so, we will advance understanding of (i) how logjams affect water quality and stream communities in forested watersheds, (ii) the effects of historical and continuing human alteration of river corridors in forested regions, and (iii) how to design artificial logjams in rivers to manage stream temperature, nutrients, and aquatic communities. Our work will be shared with resource managers and practitioners to help with issues associated with river management and restoration. Student participation will include (i) K-12 students via course materials that will be developed in collaboration with elementary school teachers; (ii) undergraduate students involved in field data collection and analysis, including students from diverse backgrounds; and (iii) graduate students responsible for the primary data analysis and interpretation, who will have the opportunity to work with and mentor the undergraduate researchers.The benefits of large wood (LW) in river corridors are numerous, including the potential to enhance hyporheic exchange flow (HEF). Existing work has focused on HEF near single logs or single logjams. However, natural channels in forested regions with minimal human alteration commonly contain abundant dispersed LW pieces and multiple logjams spaced irregularly along the channel. We have little indication of whether multiple channel-spanning logjams produce an additive or nonlinear effect on HEF, but these alternatives have important implications for understanding river ecosystem function and for river management and restoration. Our primary objective is to quantify how HEF changes with increasing channel heterogeneity associated with channel-spanning logjams. We will use field measurements, physical experiments, and numerical models to evaluate the characteristics of HEF associated with different spatial densities of channel-spanning logjams. We expect nonlinear relations between logjams and HEF to result from increased bedforms such as pools that maximize flux rates, increased head gradients associated with decreased downstream spacing between logjam-induced backwaters, and thicker deposits of sand and gravel, which act together to create steep hydraulic head gradients within thick, permeable bed sequences. We also expect a nonlinear relation between logjams and HEF at the transition to anabranching as a result of the enhanced HEF between divided channels. Implications of this work will be with respect to engineered logjams, which are currently being added to rivers, but with no systematic understanding of how the effects of LW addition scale with river size, the volume and spatial distribution of wood addition, or the characteristics of the wood and the channel, constraining our ability to design LW-based river restoration to achieve a desired level of HEF. As part of our research, we will develop curriculum for a local K-12 school.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.