Rapid monitoring of river hydrodynamics and morphology using acoustic holography

Lead Research Organisation: University of Sheffield
Department Name: Civil and Structural Engineering

Abstract

Accurate flow measurement in rivers is vital to build well calibrated, reliable simulation models able to predict accurately the timing and extent of floods, and also to provide the data needed for effective management of water resources in a river catchment. This project will develop a new method of acoustic wave holography to measure remotely the velocity, flow depth and bed characteristics within river channels. The proposed holography method records the pattern of reflected acoustic waves (the hologram) above a dynamic flow surface and uses this pattern to reconstruct the water surface wave field throughout a three-dimensional region of space. The project will use recent advances in computational fluid mechanics and turbulence theory. The underpinning concept is that the free surface of turbulent river flows is never flat and is always dynamically rough. There is overwhelming evidence that the 3-dimensional pattern of the free surface of a river flow is caused by the turbulence structures within the flow. These structures are generated at the river bed and rise to the free surface and express themselves in the form of a pattern of surface waves which propagate at a particular velocity which does not necessarily coincide with the mean surface water velocity. Therefore, the free surface wave pattern carries comprehensive information about the underlying hydrodynamic processes in the flow, including the flow velocity, depth, turbulence scale and intensity and bed roughness characteristics. This process is very complex and it has not been sufficiently studied in the past because of a lack of accurate and robust instruments and accurate fluid dynamics models to relate the free surface wave pattern to the flow structure beneath. Thus, there is now an opportunity to develop a clear understanding how the pattern observed on the free surface of a river flow and the underlying turbulence structures and bed surface roughness in fluvial environments interact. This new knowledge in the hydrodynamics of turbulent river flows combined with new acoustic holographic measurement capabilities will provide a paradigm shift in the accuracy, spatial resolution and speed of deployment of flow monitoring in rivers. In this respect, the proposed work has a very high degree of novelty in comparison to the broader research context of this area internationally.
The proposal is timely because it will contribute significantly to the need for us to better understand our natural environment especially under extreme conditions and in the development of Robotics and Autonomous Sensor technologies. These technologies were outlined in a report by David Willetts as one of the "Eight Great Technologies" that should be promoted and developed by the UK. The Willetts' report also states a clear need for real time forecasting of rivers, better water resource management and autonomous surveillance vehicles which require accurate on-board sensing. Our project takes an important step towards providing technology to address these requirements. The new sensor technology will also enable new theoretical foundations to be developed in the areas of wave propagation, inverse problems, holography, signal processing and computational fluid dynamics.

Planned Impact

This project will result in new acoustic wave holography technology with the capability to rapidly survey the hydrodynamics of river channels non-invasively with an unprecedented degree of spatial and temporal resolution and spatial scale. This capability is important for assessing flood risk, channel morphology change, pollution risk from intermittent discharges, and the flow hydrodynamics controlling the quality of the physical habitat in rivers. The following groups will benefit from this work: (i) short-term (duration of project) - flow survey instrument and sensor developers and manufacturers; (ii) medium-term (up to five years) - environmental consultants and government statutory bodies; and (iii) long-term (five to ten years) - governmental regulators, non-governmental organisations (NGOs) and general public.
1. A sensor manufacturer is involved (see LoS from Gesellschaft für Akustikforschung Dresden mbH). This organisation will benefit in terms of a much better physical and mathematical understanding of the link between the hydraulic flow characteristics and the free surface, acoustic field properties scattered by the free surface and ability of the signal processing system to infer more accurately the true characteristics of the water surface from the recorded acoustic data. Other flow monitoring companies will be engaged via the project workshops. The better understanding of the physics and underpinning mathematics will enable the design more accurate, lower cost flow measurement instruments which will be commercially viable and have high market value. The flexible deployment of the sensor technology can be achieved by working with providers of field drone sensor deployment platforms.
2. The project benefits from the involvement of the EA, NRW, USEPA, ICHARM and other commercial project partners (HR Wallingford, JBA) (see LoSs). Their active involvement in the steering of the work and provision of data and testing sites will ensure that the outcomes of our work will be of high importance to government and statutory bodies and consultants engaged in water resource and river management. For example, the EA/NRW have a statutory duty under the Floods Directive to assess and manage flood risk. This is accomplished by mapping flood extent and devising adequate measures to reduce flood risk. This uses calibrated river models which are calibrated using sparse data collected at low flow conditions. The monitoring technology to be developed will allow more widespread and higher quality measurement at all flow conditions. The Water Framework Directive (WFD) requires the EA/NRW to develop programs of measures to ensure rivers have good ecological status. Accurate monitoring of the spatial and temporal hydraulic changes in rivers is of paramount importance for assessing ecological status because it controls biota-flow feedbacks and potential contaminant transport. Thus our developed technology is likely to be a core tool in NRW/EA's work by providing spatial hydrodynamic data to assess the ecological status of river reaches. Both flood risk assessment and WFD assessment modelling is performed by consultancies. The detailed data obtained from holographic sensing will provide new understanding of river hydraulics for consultancies and government statutory bodies involved in the management of water resources, prediction of flood risk, sediment movement and consequent morphological changes.
3. The ability to collect low cost flow data at multiple sites within a river catchment will over the longer term provide better assessment of the hydrological capacity of a river basin. This will lead to the improved management by governmental bodies of water resources. NGOs and the general public will benefit in terms of improved flood risk management and better ecological status achieved through provision of better, more plentiful temporal and spatial hydraulic data, which will also raise public awareness of potential ecological impacts.

Publications

10 25 50
 
Description It has been shown that it is possible that by undertsanding the water dispersion characteristics that the depth and depth avaeraged flow velocity is a river can be estimated. This means that a truely non-contact flow rate measurement for rivers is now possible. This technique was demonstrated at an Environment Agency gauging station on the River Sheaf in Sheffield.
Exploitation Route This finding will need to be developed further to examine its range of applicability.
Sectors Environment

 
Title Data on frequency-wavenumber spectra of water waves from videos of the river surface: River Sheaf, UK, Feb-Jun 2019. 
Description This data set contains sequences of orthorectified images of the free surface of the River Sheaf, Sheffield, United Kingdom (Latitude: 53.373056$^\circ$ Longitude: -1.463913$^\circ$ (WGS 84)), recorded between February and June 2019, as well as their 3D space-time Fourier power spectrum, and gauging survey data of the stage and flow discharge. doi: 10.5281/zenodo.3670647 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
Impact This data supports the validation of a new technique able to estimate the flow discharge of a river based on videos of the river surface. 
URL https://zenodo.org/record/3670647#.XmZuymj7S00
 
Title Measurements of sound reflected from a dynamic water surface. 
Description This data set includes measurements of the acoustic field reflected by a moving rough water surface. 1D water waves with both narrow and broad spectra were produced in a wave flume. 2D patterns caused by the interaction of a turbulent flow with the bed roughness were measured in a laboratory flume with constant slope. Different types of acoustic excitation (sine sweep, white noise, harmonics) were tested, and recorded with multiple microphones arranged in 1D and 2D arrays. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact This data will demonstrate the capability of the technique developed during this project to determine the temporal-spatial statistical behaviour of a dynamically moving water surface. The analysed data will inform a future publication, to be submitted before the end of the project. 
 
Title Measurements of sound reflected from a set of static rough surfaces 
Description This data set contains recordings of sound reflected from acoustically rigid rough surfaces with a variety of roughness statistics. Different types of incident signals (sine sweeps, white noise, harmonics) in the frequency range 10-25 kHz have been tested. The recordings were performed at various heights from the surface using arrays of 17 or 34 microphones. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact This data informed a publication in conference proceedings (Experimental Surface Shape Reconstruction Using Microphone Arrays, Forum Acusticum, Lyon, 2020), currently under review. Additional analysis of the same data set will be included in a journal article currently in preparation. 
 
Title database of acoustic noise background in the vicinity of a drone flying over a river 
Description Acoustic field measured with miniaturised microphones directly attached below a UAV flying over a river. Various types of UAV and fly paths/protocols were tested. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? No  
Impact These data inform the design of acoustic arrays installed on flying vehicles. Broadband high-frequency and high-intensity noise produced by the UAV during operation suggests the need to carefully design the measurement array and signal in order to minimise data contamination. 
 
Description Karlsruhe Institute of Technology - Dr Akutina 
Organisation Karlsruhe Institute of Technology
Country Germany 
Sector Academic/University 
PI Contribution Dr Akutina was hosted in Sheffield, where, the team shared their knowledge and expertise of free surface dynamics and measurement techniques in open channel flows, and gave a demonstration of the capabilities of the existing measurement facilities.
Collaborator Contribution The collaborator shared knowledge of flow and free-surface measurements in open channel flows using particle tracking velocimetry, and assisted during the design of the new measurement rig.
Impact Design of Particle Tracking Velocimetry (PTV) instrumentation in the laboratory open channel flume.
Start Year 2018
 
Description Kobe University - Prof Fujita 
Organisation Kobe University
Country Japan 
Sector Academic/University 
PI Contribution Members of the team shared their expertise on surface waves dynamics in turbulent flows during reciprocal visits to Sheffield and Kobe. The collaborators were given access to the laboratory facility in Sheffield, where they took some optical measurements of the free surface of an open channel flow, to complement their existing experiments performed previously in Kobe.
Collaborator Contribution The collaborators shared their expertise on optical measurements of a river surface during reciprocal visits to Sheffield and Kobe. Members of the team were hosted in Kobe, where they assisted to a demonstration of the experimental facilities, and at a field site along the Shinano River, in Japan. In this occasion, the collaborators gave access to a number of UAVs to allow recording the acoustic noise background field in the vicinity of a drone while flying over a river along typical measurement paths.
Impact database of acoustic noise background in the vicinity of a drone flying over a river
Start Year 2018
 
Description Newcastle University - Dr Perks 
Organisation Newcastle University
Country United Kingdom 
Sector Academic/University 
PI Contribution The research time provided an innovative algorithm to estimate a river discharge from videos of the water surface.
Collaborator Contribution The collaborators collected and shared a set of videos of the river Sheaf, according to specifications provided by the team, in order to facilitate the analysis.
Impact _ data set: Data on frequency-wavenumber spectra of water waves from videos of the river surface: River Sheaf, UK, Feb-Jun 2019. doi: 10.5281/zenodo.3670647 _ conference paper: The effect of surface gravity waves on the measurement of river surface velocity. River Flow Conference, Delft, The Netherlands, 2020. Accepted for publication. _ journal article: Analysis of Surface Wave Image Spectrum to Estimate River Discharge. Manuscript submitted to Geophysical Research Letters. Under review.
Start Year 2018
 
Description Siemens 
Organisation Siemens Digital Industries Software
Country United States 
Sector Private 
PI Contribution The team provided data analysis procedures and computer scripts to extract spatial information (shape, acoustic impedance distribution) of a reflecting surface based on measurement of the scattered acoustic field at multiple locations.
Collaborator Contribution The collaborators gave access to specialised equipment, namely sets of microphones, acquisition system, and acoustic camera, and provided the required training for their use. They also gave access to their experimental facilities in Leuven, and provided staff hours for two sets of tests in Leuven and in Sheffield.
Impact conference paper: Experimental Surface Shape Reconstruction Using Microphone Arrays. Under review. data set: Measurements of sound reflected from a set of static rough surfaces. data set: Measurements of sound reflected from a dynamic water surface.
Start Year 2018
 
Description UK Environment Agency - Dr Everard 
Organisation Environment Agency
Country United Kingdom 
Sector Public 
PI Contribution Members of the team participated to a EA workshop on surface velocity-based hydrometry as expert contributors. There, they provided training on advanced non-contact river monitoring techniques to member of the Agency. Research developed by the team under this grant has been applied to a pilot site in Sheffield. The results will inform the hydraulic characterisation of the field site.
Collaborator Contribution Dr Everard has contributed to the promotion of the research under this grant to a wide list of national and international contacts, including research staff at universities (Newcastle University, University of Hull), research centres (IRSTEA Villeurbanne, France), companies (Electricite de France, France, PhoTrack, Switzerland), and agencies (Scottish Environment Protection Agency, Norwegian Water Resources and Energy Directorate). These contacts were instrumental for the collaboration with Newcastle University. Personnel of the UK Environment Agency has helped during the collection of hydraulic data, and shared existing data of the River Sheaf. This data was fundamental for the validation of the measurement techniques developed as part of the project.
Impact _ data set: Dolcetti, G., Hortobagyi, B., Perks, M., & Tait, S. (2020). Data on frequency-wavenumber spectra of water waves from videos of the river surface: River Sheaf, UK, Feb-Jun 2019. doi: 10.5281/zenodo.3670647
Start Year 2018
 
Description IMechE event - technical visit: Laboratory for Verification and Validation, Sheffield 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Technical visit to the LVV facility organised for the Institution of Mechanical Engineers. A member of the team gave a brief presentation about the aims of the project, followed by demonstration of the experimental facility and Q&A. The project attracted a lot of interest from the attendees, with prolonged discussion and questions.
Year(s) Of Engagement Activity 2019
 
Description Presentation to Surface Velocity Discharge Methods Workshop 23-25 Nov 2018 organised by the Environment Agency 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact This was a workshop organised by the Hydrometry Section of the Environment Agency to examine and disseminate the latest advances in surface velocity measurement. It was held over 2 days at the Environment Agencies offices at HR Wallingford. The audience comprised mainly of technical staff from different Environmental regulators from the rest of the UK and Scandinavia.
Year(s) Of Engagement Activity 2018
 
Description presentation - Workshop in Structural Dynamics, Sheffield 2019 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact This was part of an international workshop on structural dynamics organised by the Dynamic Research Group of the University of Sheffield. Audience included researchers as well as practicioners and representatives of industries, mostly of the aerospace sector (e.g., Boeing, AirBus). A member of the team gave a 20 minutes presentation, followed by a practical demonstration of the experimental setup and one-to-one Q&A during specially allocated time. The audience showed interest regarding applications for monitoring of wind turbines in marine environments.
Year(s) Of Engagement Activity 2019