What type of gully is that? The need for a classification of gullies

Abstract

Despite over a century of investigations into gullies and gully erosion, the characterization and categorization of gullies and the varied definitions, nomenclatures and terminology used has caused some confusion in understanding and communicating the relationships of gully forms and processes around the world. We firstly review the gully literature and highlight how a lack of consistency in gully definition and characterization prevents unifying theory from being developed within this important field of research, since it is often unclear whether different landscape features being discussed are comparable. We propose that conventionally employed qualitative planform and cross‐sectional characteristics of gullies alone are inadequate to define gully types, yet both these features remain central to most modern gully descriptions. We discuss the need to revise and augment these basic characteristics with clearly defined morphogenetic attributes such as landscape context, soil material characteristics, erosion processes, hydrological integrity, modes of development, and head/side‐wall morphology for an effective, practicable, generic gully classification scheme. Central to a gully classification scheme is the need for a clear definition of what a gully is – and is not – for which geomorphological criteria are proposed to differentiate a ‘gully’ from other ‘incisional land surface forms’. This gully definition hinges largely on the identification of a retreating head scarp and the internal erosion by mass‐movement and other sidewall slope erosion processes, coupled with the transport of the soil materials from the gully void. By defining a gully and synthesizing descriptions of gully ‘types’ from the literature and our own experience, we propose key morphogenetic attributes of gullies necessary to form a framework for a systematic gully classification scheme. An initial, eclectic classification framework is presented as both a summation and a synthesis of the literature review, and as a progenitor to a dynamic generic classification scheme that is proposed in a follow‐up article.

Achieving change through gully erosion research

“…Developing more specific knowledge of vegetation management to reduce or avoid gully and piping erosion remains an important work in progress (e.g., Talema et al, 2019). At broader scales, classification of gully features and their settings (e.g., Thwaites et al, 2021) can be useful for targeting specific management approaches to settings where they have been successfully tested, and for guiding the global transfer of research findings.…”

Processos erosivos e dinâmica de duas voçorocas desenvolvidas em solo residual em uma encosta íngreme (Estado do Espírito Santo, Brasil)

“…Voçorocas são incisões superficiais bem definidas que podem alcançar até dezenas de metros de profundidade, largura e extensão (GUERRA, 2007). De acordo com Thwaites et al (2022), as voçorocas possuem paredes ou escarpas e são condicionadas por fluxos efêmeros. Segundo DAAE/ IPT (1990), uma das características das voçorocas é que devem interceptar o lençol freático.…”

Gullies and badlands of India: Genesis, geomorphology and land management

“…Gullies are products of deeply channelised soil erosion that have been studied for over a century (Castillo and Gómez, 2016). Termed differently in different parts of the world (Wells, 2004;Castillo and Gómez, 2016;Thwaites et al, 2022), gullies have been classified with respect to their landscape position (i.e. valley-bottom, valley-side and bank gullies) (Begin and Schumm, 1979;Poesen et al, 2002;Morgan and Mngomezulu, 2003) and their permanence (i.e.…”

“…Recently however, a generic gully classification system has been proposed that considers landscape surroundings, local soil characteristics, hydrology and erosion processes, modes of formation and morphology (cf. Thwaites et al, 2022).…”

“…Gullies are products of deeply channelised soil erosion that have been studied for over a century (Castillo & Gómez, 2016). Termed differently in different parts of the world (Castillo & Gómez, 2016; Thwaites et al, 2022; Wells, 2004), gullies have been classified with respect to their landscape position (i.e., valley‐bottom, valley‐side and bank gullies) (Begin & Schumm, 1979; Morgan & Mngomezulu, 2003; Poesen et al, 2002) and their permanence (i.e., ephemeral and permanent gullies) (Castillo & Gómez, 2016; Poesen et al, 2003). Recently, however, a generic gully classification system has been proposed that considers landscape surroundings, local soil characteristics, hydrology and erosion processes, modes of formation and morphology (cf.…”