Location: Watershed Physical Processes Research2013 Annual Report
1a. Objectives (from AD-416):
(1) Make use of available Light Detection and Ranging (LiDAR) data, rainfall data, and historical and on-going measurements of sediment yield from 24 field-scale watersheds in central Iowa to validate predictions of a recently developed, field-scale, distributed erosion and ephemeral gully calculator. (2) Compare predicted ephemeral gully channel locations and properties with ground-truth observations obtained using survey and photogrammetric techniques.
1b. Approach (from AD-416):
1) Analyze historic and contemporary rainfall and runoff data available from the South Fork Watershed (2 sites, 12 years to date), the South Walnut Creek Watershed (12 sites, 6 years), and Clear Creek Watershed (10 sites, 3 years). Compare observed monthly rainfall and rainfall intensity values to the long-term county-level averages that serve as RUSLE2 climatic inputs. Compare the observed runoff event population to the statistical distribution of runoff events predicted by RUSLE2 for each sub-watershed. 2) Apply beta version of the distributed erosion and ephemeral gully calculator to model the above 24 research-scale basins and compare predictions of sediment yield, gully location, and gully channel dimensions to measurements collected by cooperators. 3) Validate the channel locations predicted from existing Light Detection and Ranging (LiDAR) data by comparison with field observations of gullies mapped by cooperators using a global positioning system (GPS). 4) Validate the new ephemeral gully model by comparing predicted channel cross sections with measurements collected by cooperators using stereo photogrammetry and real-time kinematic GPS techniques following gully-forming runoff events.
3. Progress Report:
Work under this agreement includes development of techniques and materials to determine changes in ephemeral gully size using photogrammetric techniques and the analysis of historic and contemporary erosion and sediment yield observations in comparison with modeled results. Toward this end, techniques were developed to extract needed data from photographic image pairs using commercially-available software (Photo Modeler Scanner 2012). Equipment was developed to acquire images using 16-mega-pixel digital cameras with Nikon AF NIKKOR 20mm f/2.8D lenses mounted approximately 2 m above the soil surface. The first iteration of this equipment was based on a cart upon which two cameras were mounted. When this approach proved unwieldy, an alternative arrangement based on a single camera mounted on a backpack frame was developed and provided to researchers at Iowa State University who used it to periodically acquire and analyze image pairs. A trip was made to Iowa to install permanent markers (tent stakes) straddling ephemeral gullies with twelve small gauged watersheds located within the Neil Smith Wildlife refuge. Sets of four stakes were spaced 10 to 20-meters apart along the flow path of the gullies. A survey-grade Global Positioning System (GPS) was used to survey the position and elevation of each numbered marker so that each marker could be used as control points to rectify image pairs collected periodically following runoff and erosion events. 1-m Light Detection and Ranging (LiDAR) topographic data, a 2-m resolution GPS survey data, and historical rainfall and runoff data were initiated and acquired from the Neal Smith watersheds. A poster was jointly created for presentation at the annual National Institute of Food and Agriculture (NIFA) project leaders’ meeting.