Location: Watershed Physical Processes ResearchTitle: A GIS focal approach for characterizing gully geometry
|CASTILLO, CARLOS - University Of Cordova (UCO), Spain|
|MOMM, HENRIQUE - Middle Tennessee State University|
|Wells, Robert - Rob|
|Bingner, Ronald - Ron|
|PEREZ, RAFAEL - University Of Cordova (UCO), Spain|
Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/2021
Publication Date: 3/29/2021
Citation: Castillo, C., Momm, H.G., Wells, R.R., Bingner, R.L., Perez, R. 2021. A GIS focal approach for characterizing gully geometry. Earth Surface Processes and Landforms. 46:1809-1827. https://doi.org/10.1002/esp.5122.
Interpretive Summary: Gully formation and evolution are impacted by cross-section variability. Gullies are a significant source of sediment that can produce many problems associated with downstream water quality and can produce significant disruptions in local topography and farming practices. Understanding the impact of local and nearby topography to different aspects of gully channel morphology is the focus of this study. Changes in gully cross-section morphology were studied in several gully catchments in the Campiña landscape of Southern Spain. Many of the relevant factors included thresholds for gully headcut movement upstream and termination of the gully downstream that were obtained from new factors that normalized aspect and the number of channels when compared with standard approaches based on the local calculation of the slope and drainage area. The accumulated incision affecting cross-sections were satisfactorily predicted from the derived equations by incorporating the classic stream power component, the impact of the adjacent slope, the presence of woody vegetation and gully-bed resistance. Mean bank slope and cross-section shape were influenced not only by the resistance of the incised materials, but also by sedimentation processes that tended to produce U-shaped morphologies in the downstream reaches. The empirical equations derived to predict gully cross-section dimensions would be useful for planners, technicians or practitioners in developing gully erosion risk analyses and in the design of remediation plans, since they offer guidance on the differential vulnerability between gully cross-sections.
Technical Abstract: The exploration of the sources of cross-section (XS) variability in gully forms has only rarely been investigated. In this paper we examine the explanatory factors behind the changes in XS morphology in a set of gully catchments in the Campiña landscape in Southern Spain characterized by annual crops, vertic soils and soft parent materials. The study period was selected starting at a date where gullies were filled (April 2009, baseline), including a extraordinary cycle of rainfall events (2009 and 2010 winters) and ending at a date when a precise Digital Elevation Model (2-m resolution) was available in May 2014. We propose a GIS focal approach (around the neighbourhood of a pixel) for the analysis of environmental factors in order to delineate gully networks and predict gully morphology (gully depth and bank slope). Accurate predictions of thresholds for gully initiation (headcuts) and finalization (mouths) were obtained by including new factors (such as the the normalized aspect or number of channels) when compared with standard approaches based on the local calculation of the the slope and drainage area. The accumulated incision at the XS level was also satisfactorily predicted by incorporating to the classic stream power component, the impact of the adjacent slope, the presence of woody vegetation and gully-bed resistance (estimated through the undrained shear strength in a vane-test field campaign). An adaptive focal strategy with varying window sizes produced better results than the local (pixel-based) approach, requiring larger calculation scopes in areas of greater DEM uncertainty. Mean bank slope and XS shape were influenced not only by the resistance of the incised materials, but also by sedimentation processes that tended to produce U-shaped morphologies in the downstream reaches.