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River hydraulics, morphology, and vegetation: A case for improved knowledge and numerical model capabilities

Periodic Reporting for period 1 - River-HMV (River hydraulics, morphology, and vegetation: A case for improved knowledge and numerical model capabilities)

Reporting period: 2015-10-01 to 2017-09-30

This fellowship’s novel and timely research focused on improving the interdisciplinary knowledge and ability for river managers to effectively predict flood risks, restore rivers, and assess future alterations are currently restricted to the limited understanding of how river hydraulics, morphology, and vegetation alter a river’s planform, effect sediment mobility, and control the surrounding habitats. To improve this knowledge and capabilities, this research focused on the following three objectives: 1) conduct physical model flume experiments to quantify the hydraulic, morphologic, and vegetation interactions of a braided channel as well as investigate the use of manipulated channel avulsion as an innovative method to increase a river’s floodplain conveyance, 2) quantification of the accuracy of a cutting-edge numerical model’s simulations, and 3) implement new functionality within the said numerical model to improve the accuracy based on objective 2.

These issues, or gaps in knowledge, are important to society as the processes of river hydraulics, morphology, and vegetation (i.e. River-HMV) remain significant challenges to river managers, and thus reduce their ability to effectively manage and restore rivers. The increased knowledge of this research and freely available data will further enable current students, researchers, and practitioners to understand these complicated relationships and apply this knowledge and data to future applications and research. This is important because a key component to effective river management is the ability to predict channel adjustments. Armed with the knowledge and improved model capabilities of this research, river managers can better serve and protect the local socio-economics through improved flood risk assessments, appropriately estimated sediment mining, and enhanced ability to evaluate the conditions of current and future manipulations. These issues are certainly a high priority in Europe where an ambitious increase in water protection and flood risk assessments have been implemented through the Water Framework Directives (WFD) and Flood Directive (FD) legislation.
This Marie Skłodowska-Curie Individual Fellowships has completed the 24 month contract. In this time, the objectives have been pursued and research results have been successful. The following results and current standings of this research, including publication and dissemination are discussed in the objectives they were originally proposed.

Objective 1: Using flume experiments to quantify the River-HMV processes and investigation of avulsion manipulation.
Flume experiments were conducted between June 2016 to February 2017. In this objective, 135 datasets captured the River-HMV interactions of both non-manipulated conditions, as well as naturally occurring and manipulated avulsion. Beyond the processes, these high-quality datasets and the DEMs that were captured provided rich datasets for the numerical model Delft3D (discussed in more detail in the following sections).
Initial results have shown that small flood events with manipulated avulsion can produce similar vegetation removal and morphologic changes as large floods without avulsion. This data is still under review, but initial results seem promising as it suggests that river managers and restoration efforts can have greater impacts on degraded or vegetation encroached rivers despite lower flow rates.

Dissemination: These avulsion results were presented to the 2017 European Geoscience Union (EGU) as an oral presentation. Further, the novel and unprecedented SfM accuracy achieved in this research will be presented at the upcoming American Geophysical Union (AGU, 2017) as a poster presentation, and the avulsion data in greater detail will be presented at the AGU as an oral presentation. Current plans for a publication will utilize these flume experiments and quantified data in combined numerical modeling with D3D+ (discussed in greater detail below), where the numerical model can help determine the potential for a river planform’s morphologic and vegetation reactions to non-manipulated and manipulated avulsion.

Objective 2: Evaluation of Delft3D’s accuracy to reproduce the observed River-HMV processes.
The flume experiments discussed in Objective 1 provided high quality input data for the numerical model. Such datasets were recorded frequently, with 6 datasets per experiment, and thus provided high special and high temporal datasets. These datasets along with the experiment conditions were utilized in the numerical model and were the foundation for calibration and validation. However, beyond the proposed work of flume experiments, this research utilized a state-of-the-art time lapse camera method to identify sediment transport in the flume experiments. Incorporating these data provided a novel and timely examination to the numerical model’s ability to predict instantaneous sediment transport. This has never knowingly been tested and these rich datasets for a braided river provided a unique and valuable assessment and validation of the model’s ability to replicate observed conditions.
Dissemination: This model calibration and validation were presented at the 2017 EGU as an oral presentation. Further, these data have been collated into a publication to the international journal Advances in Water Resources and recently accepted but requires revisions.
Objective 3: Improving the numerical model Delft3d’s functionality.
During the planned secondment at Deltares during July 2017, I collaborated with Erik Mosselman, Jasper Dijkstra, and Mijke van Oorschot where we utilized my high-quality datasets with recent developed coding in MatLAB that would update the river’s vegetation presences based on morphology. This code has been implemented with the Delft3D to develop the proposed D3D+, and initial validation has shown that this code improves the ability of Delft3D to represent the observed vegetation presence and removal due to river morphology. At this time, more simulations need to be ran for validation of smaller flood events. Once this is completed, these data and results will be collated into a publication in collaboration with the Deltares people.
This research has gone beyond the state of the art and the expected and proposed results. Examples include, but not limited to:

1. exceeding the current state of the art application of SfM, which produced millimeter accuracy of flume topography as well as provided river bed topography of the inundated channels – both have remained challenges for the research community.
2. Incorporated time lapse technique that mapped the sediment transport intensity with numerical model calibration and validation.
3. Quantified the potential for avulsion manipulation to be utilized as a creative approach to floodplain re-activation and a potential method for combating vegetation encroachment.

Such results, and their current disseminations and ongoing publications are anticipated to:
1. Provide new evidence and methods in river management and restoration
2. Accelerate the use and value of SfM in laboratory experiments
3. Provided new functionality and improved simulated accuracy for numerically modeling rivers with vegetation.
4. Provide greater opportunities for future researches to investigate the interactions of river hydraulics, morphology, and vegetation through the use of the improved D3D+.