News

A little bit more detail on individual research outputs, field campaigns, comings and goings, and goings on ...

 
 
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2017 AGU Fall Meeting, New Orleans, LA, 11-15 December

Go say hi!!

Grams, P.E., Buscombe, D. Topping, D.J., Mueller, E.R. (2017) Identification of discontinuous sand pulses on the bed of the Colorado River in Grand Canyon.

Leary, K., Buscombe, D., Schmeeckle, M., Kaplinski, M. (2017) Assessing the Importance of Cross-Stream Transport in Bedload Flux Estimates from Migrating Dunes: Colorado River, Grand Canyon National Park. 

Platt, A. S., Buscombe, D., Porter, R. C., & Grams, P. (2017), Estimating Sediment Thickness from Riverbed to Bedrock within the Colorado River in the Grand Canyon. 

 
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October 2017. Figure from our paper selected for the front cover of the October 2017 edition of the Journal of Geophysical Research - Earth Surface

Figure shows example imagery for each of 10 unique substrate classes easily identifiable by eye from our underwater video system (LOBOS), arranged in two groups of five. The first group are found in sites where the riverbed is completely unvegetated (top four rows). The second group (bottom four rows) are found in partially vegetated riverbeds. The substrate codes shown in the first image in every group are those defined in Table 1 and colored the same as how they are represented in Figure 2 in the following paper: 

Buscombe, D., Grams, P. E., & Kaplinski, M. A. (2017). Compositional signatures in acoustic backscatter over vegetated and unvegetated mixed sand-gravel riverbeds. Journal of Geophysical Research: Earth Surface, 122, 1771–1793. https://doi.org/10.1002/2017JF004302

 
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October 2017. Article published in Journal of Geophysical Research - Earth Surface

Multibeam acoustic backscatter has considerable utility for remote characterization and mapping of spatially heterogeneous bed sediment composition over vegetated and unvegetated mixed sand-gravel riverbeds of mixed sand and gravel from a moving vessel.

However, high-frequency, high-resolution acoustic backscatter collected in shallow water is hampered by significant topographic contamination of the signal. In this paper, a two-stage method is proposed to filter out the small-scale topographic influence on acoustic backscatter. This process strengthens relationships between backscatter and sediment composition.

A probabilistic framework is presented for classifying vegetated and unvegetated substrates based on acoustic backscatter at decimeter resolution. This capability is demonstrated using data collected from diverse settings within a 386 km reach of a canyon river whose bed varies among sand, gravel, cobbles, boulders, and submerged vegetation.

Buscombe, D., Grams, P. E., & Kaplinski, M. A. (2017). Compositional signatures in acoustic backscatter over vegetated and unvegetated mixed sand-gravel riverbeds. Journal of Geophysical Research: Earth Surface, 122, 1771–1793. https://doi.org/10.1002/2017JF004302

 
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September 2017. Presented at the Rivers, Coastal and Estuarine Morphodynamics ("RCEM 2017") Symposium in Padova, Italy.

Many scaling relationships have been proposed to link subaqueous sand dune dimensions with aspects of flow. This is useful for estimating dune dimensions from flow depth and velocity, which can be used to estimate dissipation of flow energy, bottom turbulence generation and bedload sediment transport.

However, when data is compiled from rivers worldwide, one observes a more than order of magnitude variation in dune height or length for a given flow depth. Why? We investigate using a very large data set collected from the Colorado River in Grand Canyon. We find that dune dimensions are controlled by grain size and degree flow constriction.

 
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October 2017. New sensors installed on the Chippewa River, WI, to measure "total load" 

A new project has started in collaboration with the USGS Minnesota and Wisconsin Water Science Centers, and the Grand Canyon Monitoring and Research Centers, whose goal is to quantify 'total load' on the Chippewa River. Total load refers to the amount of sand moving both in suspension and as bedload. We have installed acoustic sensors to measure both components of load near Durand, WI. The aim is to continuously measure suspended sediment and track dunes moving along the bed to estimate bedload. The sensors will be in place for 3 years and will be used to estimate the amount of sediment that is entering Lake Pepin, hence the requirements for sediment management in the reservoir.

 
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August 2017. Presented at the American Fisheries Society annual meeting in Tampa, Florida.

In the past few years, low-cost, consumer-grade (hereafter, ‘recreational-grade’, to distinguish from ‘survey’ or ‘scientific’ grade) sidescan sonar platforms, have been developed for leisure activities such as fishing and hobbyist archeology. Recreational-grade sonar lack standardization in (and description of) the acoustic signal processing used, often without high-quality (‘survey grade’) positioning and measured boat attitude (heave, pitch, yaw, etc), and reporting of those quantities. It is not usually possible to process data from such sonars using conventional commercial hydrographic surveying software, to post-process the positioning of the scans or carry out a calibration that corrects for radiative properties of individual transducers. However, these inexpensive, lightweight (portable) sidescan sonar units can be deployed on almost any waterborne craft without the requirement of specialist knowledge of sonar and geodetics, and with little to no experience with acoustic remote sensing. This accessibility is behind the rapid increase in popularity of these sonar systems, among the scientific research community for benthic imaging in a range of aquatic environments, both marine and freshwater, lotic and lentic

A special session was held on using low-cost sonar technology in rivers and streams to support. I presented on the development of PyHum program and the ongoing developments in automated bed sediment characterisation from recreational grade sidescan sonar systems.

 
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April 2017. Channel Mapping in Western Grand Canyon

They said it couldn't be done. 60 miles of channel mapped in 2 weeks, with a crew of 25, 7 boats, 2 multibeam sonars, 1 boat-mounted lidar, 1 sub-bottom profiler, 1 sidescan sonar, 1 underwater video camera system, 4 robotic total stations, and lots and lots of gunners and nams!!

 
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March 2017. Article published in Environmental Modelling and Software

In recent years, lightweight, inexpensive, vessel-mounted ‘recreational grade’ sonar systems have rapidly grown in popularity among aquatic scientists, for swath imaging of benthic substrates. To promote an ongoing ‘democratization’ of acoustical imaging of shallow water environments, methods to carry out geometric and radiometric correction and georectification of sonar echograms are presented, based on simplified models for sonar-target geometry and acoustic backscattering and attenuation in shallow water. Procedures are described for automated removal of the acoustic shadows, identification of bed-water interface for situations when the water is too turbid or turbulent for reliable depth echosounding, and for automated bed substrate classification based on singlebeam full-waveform analysis. These methods are encoded in an open-source and freely-available software package, which should further facilitate use of recreational-grade sidescan sonar, in a fully automated and objective manner. The sequential correction, mapping, and analysis steps are demonstrated using a data set from a shallow freshwater environment.