Predicting In-Canopy Velocity and Retention Time for Aquatic Canopies

预测水生冠层的冠层内速度和保留时间

• 批准号: 0738352
• 负责人: Heidi Nepf
• 金额: $ 38.34万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738352&HistoricalAwards=false
• 关键词: Predicting; Canopy; Velocity; Retention; Time

Predicting the Impact of Vegetation on Velocity Heterogeneity and TransportHeidi NepfAquatic vegetation impacts water and habitat quality in several ways. Aquatic plants remove nutrients and produce oxygen. They create regions of diminished bed stress that promote the retention of particles and influence morphological evolution. Both submerged and emergent canopies are known to damp waves and reduce coastal and bank erosion. Finally, by introducing spatial heterogeneity to the velocity field, vegetation increases habitat diversity, and thus species diversity. Because of its many benefits, some researchers now advocate wide spread replanting and ecologically based management of channel and coastal vegetation.Under previous grants (EAR0309188, EAR0125056), the PI has described flow and transport in long, emergent and submerged canopies, i.e. with longitudinal extent much larger than canopy height or width. These projects used rigid canopy models, which are a reasonable surrogate for emergent vegetation, but are less appropriate for submerged plants, which tend to be flexible. The continuous, rigid canopy was a necessary first step, as it is easily represented through mathematical models, allowing robust model testing. We are now ready to build on those first simple models and explore the range of canopy morphology present in nature. This work will proceed in two parts. One project will develop models for flexible canopies under both unidirectional flow and waves. The second will develop models for submerged and emergent canopies of finite length and width, geometries for which the existing two-dimensional models do not apply. The second project will again use rigid canopies to facilitate the testing of new mathematical models. The two parts have strong intellectual synergy. The students working on the two will hold group meetings and share common lab space, new ideas will be quickly transferred between projects, and each project will benefit from ongoing comparison and contrasting of different morphologies. The combined activity in vegetation hydrodynamics will also attract more visiting scholars, bringing new ideas and perspectives to the work. Second, the finite-canopy project was conceived to use rigid models. When working simultaneously, the flexible canopy project will provide insight into how one adapts rigid models to flexible canopies and will also provide a flexible canopy for testing these insights. In this way, the finite-canopy study will progress much further in extending new finite-canopy models to flexible morphologies. Third, the study of wave-damping by vegetation will be greatly expanded, because both flexible and rigid canopy models will be available in the lab. Because both lake and ocean coasts have zones of submerged flexible canopies as well as rigid emergent canopies, it is important to characterize wave damping in both zones. The work will take an important step toward field testing through experiments with real vegetation in the field-scale Outdoor StreamLab at the Saint Anthony Falls Laboratory (Univ. of Minnesota). Ecologists, geologists, and hydrodynamicists will be using the Outdoor StreamLab simultaneously, facilitating inter-disciplinary connections.

预测植被对速度异质性和运输的影响Heidi Nepf 水生植被以多种方式影响水和栖息地质量。 水生植物吸收营养并产生氧气。它们创造了床层应力减少的区域，促进颗粒的保留并影响形态进化。 众所周知，水下和浮出的树冠都能抑制波浪并减少海岸和河岸侵蚀。 最后，通过将空间异质性引入速度场，植被增加了栖息地多样性，从而增加了物种多样性。由于其许多好处，一些研究人员现在提倡对河道和沿海植被进行广泛的重新种植和基于生态的管理。根据之前的资助（EAR0309188，EAR0125056），PI描述了长的、挺水的和淹没的冠层中的流动和运输，即纵向范围远大于冠层的高度或宽度。 这些项目使用刚性冠层模型，这是挺水植被的合理替代品，但不太适合沉水植物，因为沉水植物往往是灵活的。 连续、刚性的顶篷是必要的第一步，因为它很容易通过数学模型表示，从而允许进行稳健的模型测试。 我们现在准备在这些第一个简单模型的基础上进行构建，并探索自然界中存在的冠层形态的范围。 这项工作将分两部分进行。 其中一个项目将开发单向流和波浪下的柔性顶篷模型。 第二个项目将开发有限长度和宽度的水下和浮出的冠层模型，现有的二维模型不适用于这些几何形状。 第二个项目将再次使用刚性顶篷来促进新数学模型的测试。 两部分具有很强的智力协同作用。 研究这两个项目的学生将举行小组会议并共享共同的实验室空间，新的想法将在项目之间快速转移，每个项目都将从不同形态的持续比较和对比中受益。 植被流体动力学方面的联合活动也将吸引更多的访问学者，为工作带来新的想法和观点。 其次，有限冠层项目被设想为使用刚性模型。 当同时工作时，灵活的顶篷项目将提供有关如何将刚性模型适应灵活顶篷的见解，并且还将提供一个灵活的顶篷来测试这些见解。 通过这种方式，有限冠层研究将在将新的有限冠层模型扩展到灵活的形态方面取得进一步进展。 第三，植被波浪阻尼的研究将大大扩展，因为实验室中将提供柔性和刚性的冠层模型。 由于湖泊和海洋沿岸都有浸没的柔性冠层区域以及刚性的应急冠层区域，因此表征这两个区域的波浪阻尼非常重要。 这项工作将通过在圣安东尼瀑布实验室（明尼苏达大学）的野外规模户外溪流实验室中对真实植被进行实验，向野外测试迈出重要一步。 生态学家、地质学家和流体动力学学家将同时使用户外流实验室，促进跨学科联系。