Methods for Gully Characterization in Agricultural Croplands Using Ground-Based Light Detection and Ranging

Soil erosion has long been recognized as the primary cause of soil degradation in agricultural fields (Wells et al., 2010). Overland flow in agricultural fields is the main process associated with soil erosion, which is often grouped into categories of: sheet erosion, rill erosion, and gully erosion (Smith, 1993). Traditionally, research has focussed on understanding and modelling sheet and rill erosion processes (Poesen et al., 1996). Recent research has begun to focus on addressing gully issues such as the understanding of the formation of gullies, their contribution to overall soil loss, development of tools to locate channel initiation, and appropriate measuring techniques (Poesen et al., 2003). The increased focus on gully research can be partially attributed to recent studies demonstrating that gully formation is very common on cropland, especially in conventional tillage systems (Gordon et al., 2008) and can be as significant as sheet and rill erosion in terms of sediment yield (Bingner et al., 2010). Without a good understanding of gully processes, technology cannot be developed that can provide information needed by watershed managers when evaluating and implementing effective conservation practice plans. Gullies can be generally classified as ephemeral, classical, or edge-of-field. The Soil Society of America (2001) defines ephemeral gully as “small channels eroded by concentrated flow that can be easily filled by normal tillage, only to reform again in the same location by additional runoff events”. As the headcut migrates upstream and the channel gets wider, faster than the interval between farming tilling operations, farming equipment is forced to operate around the gully and as result the gully becomes permanent (classical gully). Finally, as the name suggests, edge-of-field gullies are defined by channels where concentrated flow crosses earth bank (Poesen et al., 2003). New methodologies are being researched to understand gully formation and estimate sediment yield (Souchere et al., 2003, Cerdan et al., 2002, and Woodward, 1999). Studies use Digital Elevation Models (DEMs) as the basis to formulate theories explaining the relationship between field topography and gully occurrence (Woodward, 1999, Parker et al., 2007, and Cerdan et al., 2002). These efforts greatly benefit from accurate and detailed topographic information which can aid in the understanding of where and when gullies form and how these features evolve over time (headcut migration). Despite the availability of DEMs at regional and local scales (spatial resolution ranging from 1 to 30 meters), these datasets often do not offer the necessary spatial and/or temporal