‘Out with the Old?’ Why coarse spatial datasets are still useful for catchment‐scale investigations of sediment (dis)connectivity

Abstract

The increasing popularity of remote sensing techniques has created numerous options for researchers seeking spatial datasets, especially digital elevation models (DEMs), for geomorphic investigations. This yields an important question regarding what DEM resolution is most appropriate when answering questions of geomorphic significance. The highest possible resolution is not always the best choice for a particular research aim, and DEM resolution should be tailored to fit both the scale of investigation and the simplicity/complexity of modelling processes applied to the dataset. We find that DEM resolution has a significant effect on a simple model of bed load sediment connectivity in the Lockyer Valley, Queensland. We apply a simple bed load transport threshold to catchment DEMs at three different resolutions – 1 m, 5 m, and 25 m. We find that using a 1 m resolution DEM generates numerous disconnections along tributary channel networks that underestimates the sediment contributing area, i.e. effective catchment area (ECA), of seven tributary basins of Lockyer Creek. Utilizing a coarser (lower‐resolution) DEM helps eliminate erroneous disconnections, but can reduce the detail of stream network definition. We find that the 25 m resolution DEM provides the best measure of ECA for comparing sediment connectivity between tributary catchments. The utility of simple models and coarse‐resolution datasets is important for undertaking large, catchment‐scale geomorphic investigations. As catchment‐scale investigations are becoming increasingly entwined with river management and rehabilitation efforts, scientists need not embrace an ‘out with the old’ philosophy. Simple models and coarse‐resolution datasets can help better integrate geomorphic research with management strategies and provide inexpensive and quick first‐order insights into catchment‐scale processes that can help focus future management efforts. Copyright © 2017 John Wiley & Sons, Ltd.

Sedimentologically significant tributaries: catchment‐scale controls on sediment (dis)connectivity in the Lockyer Valley, SEQ, Australia

“…Fryirs et al , ), on the catchment DEM where cells with a slope of <1° or 2° were deleted. The original 1 m DEM was resampled to 25 m which allowed the threshold to be applied to cells that represented a significant area (Lisenby and Fryirs, in press). This prevented the deletion of small, isolated areas with localized low slopes.…”

Connectivity as an emergent property of geomorphic systems

“…Given differences in landscape connectivity relationships in differing environmental and landscape settings, there is profound variability in the ways and rates with which responses to disturbances that disrupt the sediment regime are mediated through a catchment (Fryirs et al ., , ; Lane et al ., ; Surian et al ., , ; Kuo and Brierley, , ; Lisenby and Fryirs, , ). Fryirs et al .…”

“…In this context, geomorphologists have also begun to assimilate notions of connectivity from other disciplines, especially ecology (Merriam, ; Amoros and Roux, ; Ward and Stanford, ; Ward, ) and hydrology (Pringle, , ) (cf. Bracken and Croke, ; Poeppl et al ., ), seeking to better describe water and sediment dynamics in catchment systems (Croke et al ., ; Brierley et al ., ; Fryirs et al ., , ; Turnbull et al ., ; Wainwright et al ., ; Fryirs, ; Gomez‐Velez and Harvey, ; Bracken et al ., ; Lisenby and Fryirs, , ). Depending on the respective disciplinary basis, three types of connectivity have commonly been differentiated in geomorphic contexts, although all of the types are interdependent: (1) sediment connectivity, which is the potential for sediment to move through geomorphic systems (Hooke, ) as governed by the physical coupling of landforms; (2) landscape connectivity, which is the physical coupling of landforms; and (3) hydrological connectivity, which describes the passage of the transporting medium from one part of the landscape to another.…”

“…Configuration and state are interrelated. Places in a river network with local sediment disconnectivity, for example, can accumulate sediment through time and become sites with higher potential for geomorphic change, or they can be areas that absorb change and limit manifestation of disturbance at off‐site locations (Czuba and Foufoula‐Georgiou, ; Lisenby and Fryirs, , ).…”

Mapping valley bottom confinement at the network scale

“…Using digitized streams with 10 m derived valley bottom resolution does not appear to improve the accuracy of the results using the modeling approach (Figure 13). 10 m DEMs) as an entrylevel analysis for reach-scale river typing across entire drainage networks (Lisenby and Fryirs, 2017). Hence, we are significantly encouraged by the tool's performance, even where it gets it 'wrong'.…”