Title: Analysis of topographic attributes for identification of ephemeral gully channel initiation in agricultural watersheds Authors
Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: July 30, 2011
Publication Date: August 7, 2011
Citation: Momm, H.G., Bingner, R.L., Wells, R.R., Dabney, S.M. 2011. Analysis of topographic attributes for identification of ephemeral gully channel initiation in agricultural watersheds. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE), Louisville,, KY, 7-10 August 2011. 3042-3055. Interpretive Summary: Gully sediment eroded from agricultural fields has a significant impact on crop productivity and downstream watershed water quality. Identifying where gullies form throughout watersheds can be difficult without technology utilizing the latest remotely sensed information. Knowing where gullies form can be used by watershed models to assess the impact of agricultural practices on reducing gully erosion. This study evaluated the capability of four topographic indices to identify the location of concentrated flow paths and potential gully initiation points. Each topographic index was compared to results from spatial resolutions of 25 to 200 centimeters from an agricultural field located in Kansas. Results indicated similar ability of these four indices to predict the locations of gully channel initiation points, with slightly better spatial distribution and less number of points yielded by one technique that includes not only downstream slope and upstream contributing area, but cross-slope information to identify the impact of the width on concentrating flow. Utilizing improved gully identification technology can provide action agencies with enhanced information and management tools to assess ephemeral gully erosion control practices critical in the development of effective management plans that reduces sediment loads within watershed systems.
Technical Abstract: Watershed-scale modeling tools, such as USDA’s watershed management planning tool AnnAGNPS, already have been developed with components necessary for evaluation of the effect of ephemeral gullies on farming and conservation practices; however, the identification of potential downstream gully channel initiation locations (mouths) is critical. On a watershed scale this represents a time consuming task where users may not accurately locate and describe all the existing and potential ephemeral gully mouths. Alternatively, the identification of ephemeral gully mouths are often empirically related to stream power, which is recognized as a surrogate to flow intensity and sediment carrying capacity, through the use of secondary topographic attributes. Several topographic indices have been proposed to describe stream power and thus to characterize sediment transport in overland flow specifically due to channel initiation and headcut migration. Using high spatial resolution digital elevation models (25 to 200 cm) of an agricultural field located in Kansas, USA, four topographic indices were evaluated to identify potential ephemeral gullies. Results indicated similar ability of these four indices of predicting the location of channel initiation, with slightly better spatial distribution and less number of points yielded by CTI.