Application of Close-Range Photogrammetry to Generate Physical Data of Ephemeral Gully Development.

Simultaneous achievement of agricultural sustainability and environmental quality is a grand societal challenge for the 21st century. Topsoil and nutrient losses due to ephemeral gully (EG) erosion can diminish on-farm productivity and impair off-site water quality. Commonly used soil conservation planning tools include predictive models that rarely account for EG erosion. Current and future physically based EG models must be calibrated and validated with high quality physical data of observed EGs. This research employed a technique based on close-range digital photogrammetry to generate geo-referenced, time-sequenced topographic data of EGs observed in Iowa during 2013 and 2014. EG reaches were periodically photographed in twelve experimental watersheds. Photographs were used as input for photogrammetric analyses that generated high-resolution (5mm) digital elevation models (DEMs) as raster grids, which were post-processed to determine volume changes between multiple time steps. DEM post-processing also generated EG cross-sections in tabular format. Such detailed measurements will be of high utility for the improvement of predictive soil erosion models. Advantages of the method used in this study include high data quality, rapid data collection, and relatively low labor input after field study initialization. Limitations of the approach include a need for custom-developed DEM post-processing computer code and the use of specialized photography equipment and photogrammetric software. Results from the study indicate that close-range digital photogrammetry is an effective way to produce high quality digital morphological data of EGs. Existing and future EG erosion models can be improved by the data obtained in this project, and such models can be part of a great societal solution to sustain agricultural productivity and enhance water quality.