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24
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Introduction
Hamish is a Hydrodynamics and Remote Sensing Scientist in the hydrodynamics research group at NIWA. His research focuses on the development of novel experimental methods and measurement systems. His areas of expertise include: river remote sensing, sediment transport, turbulence, flow vegetation interactions, flood measurements, bank erosion, instream habitat assessments, programming and data analysis. He leads a range of projects within these areas of research.
Current institution
Publications
Publications (24)
Discrete particle dynamics is one of the least understood aspects of river bedload transport, but in situ measurement of stone movement during floods poses a significant technical challenge. A promising approach to address this knowledge gap is to use sensors embedded within stones. Sensors must be waterproof and recoverable after being transported...
This user guide contains methods for remote sensing toxic benthic cyanobacteria cover with drones and a range of camera types (RGB, RGN, Multispectral and Hyperspectral). Methods are also provided for collecting ground truth biomass samples, performing image classifications, and estimating larger scale biomass. Case studies in this report demonstra...
This Envirolink funded advice document provides practical methods for converting from surface velocity to depth averaged velocity using ‘alpha’ (which is the ratio of depth averaged velocity to surface velocity). The accuracy of discharge measurements derived from surface velocities are highly dependent on the selection of an appropriate alpha valu...
Aquatic macrophytes are a key component of river systems around the world. Surveys of macrophyte surface cover, cross-sectional blockage and plant/patch sizes provide data for river managers to assess in-stream habitat, hydraulic resistance, and the success of stream restorations. Manual surveying techniques are labour intensive, provide low spatia...
This paper reports the morphology of a natural patch of Ranunculus penicillatus and presents high-resolution measurements of flow velocities in its wake using a stereoscopic PIV field measurement system. The patch was 3.80 m long, 1.24 m wide and caused substantial changes to downstream mean velocities and turbulence. Vertical profiles of streamwis...
The accuracy of discharge measurements derived from surface velocities are highly dependent on the accuracy of conversions from surface velocity us to depth-averaged velocity U. This conversion factor is typically known as the ‘velocity coefficient’, ‘velocity index’, ‘calibration factor’, ‘alpha coefficient’, or simply ‘alpha’, where α=U/us. At so...
Lightweight and energy-efficient structures are the cornerstones of new designs in demanding areas such as aerospace engineering. Electrically-powered Unmanned Aerial Vehicles (UAV) have widespread applications globally and are increasingly being used for high resolution surveying.
However, on-board batteries typically make up to more than one thir...
The paper reports the results of laboratory experiments to investigate the effect of vegetation patch mosaics on hydraulic resistance. Experiments were run for seven levels of vegetation coverage with square patches of flexible plastic grass in aligned and staggered configurations and a wide range of hydraulic conditions. Hydraulic resistance was s...
Remote sensing of rivers and the use of surface image velocimetry techniques is rapidly growing globally. This user guide covers a wide range of topics including: novel equipment developed during the drone flow project; surface velocimetry techniques; remote sensing river bathymetry; and conversions from surface velocity to depth averaged velocity....
A novel aerial tracer particle distribution system has been developed. This system is mounted on an unmanned aerial vehicle (UAV) and flown upstream from where surface velocimetry measurements are conducted. Tracer particles can be rapidly deployed across the full channel width and distributed in a crescent shape (for larger channels), so that they...
This paper contributes a field study of suspended sediment transport through aquatic vegetation. The study was run over a 3 month period which was selected to coincide with scheduled weed cutting activities. This provided the opportunity to obtain data points with no vegetation cover, as well as to investigate the effects of weed cutting on Suspend...
Aquatic vegetation, hydraulics and sediment transport have complex interactions that are not yet well understood. These interactions are important for sediment conveyance, sediment sequestration, phasing of sediment delivery from runoff events, and management of ecosystem health in lowland streams. To address this knowledge gap detailed field measu...
Remote gauging of open channel flow: Estimation of depth averaged velocity from surface velocity and turbulence.
Previous research has shown that seaweed health status and photosynthetic activity are reduced due to hyposaline stress, but its effects on seaweed physical properties are unknown. In this study, we begin to address this knowledge gap by investigating the effects of hyposaline stress on the morphological and mechanical properties of the kelp Saccha...
Image-based 3D measurement of size, location, and orientation of gravel grains.
The rise of drones in hydraulics reflects the demand for higher resolution data at lower cost. Drones are now affordable, reliable and easy to use, making them well suited for investigation of finer scale processes (mm to cm), compared to the landscape scales covered by aircraft and satellites. The rise of drones has also been paralleled by exponen...
Aquatic plants such as macrophytes and bryophytes inhabit many of the river systems around the world. They are primary producers that provide a 3D substrate matrix for invertebrates and small fish, but at high levels of instream biomass they can have a significant impact on flow conveyance and sediment transport. Investigation of flow interactions...
Flow-vegetation interactions occur at a wide range of scales, from the sub-leaf to the patch mosaic or river reach scale. At the larger scales, vegetation such as aquatic macrophytes can alter the flow, creating regions of enhanced or reduced turbulence and bed shear stress. This flow alteration can manifest as deposition of fine sediment in the wa...
The objective of this paper is to expand the framework of the conventional Reynolds-Averaged Navier-Stokes equations for the study of mobile-boundary flows. The temporal averaging concept is discussed first, including relevant definitions and theorems. Time-averaged continuity, momentum, mass-transport and stress balance equations are then derived....
Most environmental flows often exhibit high levels of spatial and temporal heterogeneity in hydrodynamic fields due to the effects of multi-scale roughness elements and their mobility. These effects are especially profound in the near-bed region and at low-submergence conditions typical for such flows. The conventional Reynolds-Averaged Navier-Stok...
