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

在这项建议中，我们希望量化河流形状、堵塞以及堵塞周围和周围沉积物中的水运动之间的关系。通过这样做，我们将增进对(I)堵塞如何影响森林流域的水质和河流群落，(Ii)历史上和持续的人类改变森林地区河流走廊的影响，以及(Iii)如何在河流中设计人工堵塞来管理溪流温度、营养物质和水生群落的理解。我们的工作将与资源管理人员和从业者分享，以帮助解决与河流管理和恢复有关的问题。学生的参与将包括：(I)通过将与小学教师合作开发的课程材料的K-12学生；(Ii)参与野外数据收集和分析的本科生，包括来自不同背景的学生；以及(Iii)负责初级数据分析和解释的研究生，他们将有机会与本科生研究人员合作并指导他们。已有的工作主要集中在单根原木或单根堵塞附近。然而，在人类活动最少的森林地区，天然河道通常含有大量分散的LW片和沿河道不规则分布的多个堵塞。我们几乎没有迹象表明多个跨越河道的堵塞对HEF产生加性或非线性影响，但这些替代方案对于了解河流生态系统功能以及河流管理和恢复具有重要意义。我们的主要目标是量化HEF如何随着渠道异质性的增加而变化，这些异质性与渠道跨越的僵局相关。我们将使用现场测量、物理实验和数值模式来评估与不同空间密度的横跨海峡的堵塞相关的高强度聚焦的特征。我们预计堵塞和HEF之间的非线性关系将产生于河床形态的增加，如最大流量的水池，由于堵塞引起的回水之间下游间距减小而导致的水头坡度增加，以及砂砾沉积的增加，这些因素共同作用，在厚的、可渗透的河床序列中产生陡峭的水力水头坡度。我们还预计，由于分割通道之间的HeF增强，在向分支的过渡时，对数和HeF之间存在非线性关系。这项工作的影响将涉及目前正在增加到河流中的工程堵塞，但没有系统地了解LW添加的影响如何与河流大小、木材添加的体积和空间分布或木材和河道的特性相匹配，从而限制了我们设计基于LW的河流修复以达到所需的HEF水平的能力。作为研究的一部分，我们将为当地一所K-12学校开发课程。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.