780Z0505: Grating-type sand trap in front of four vortex tubes at Bellvue Hydraulic Laboratory
Note on envelope reads, "Grating - lab to field." See "228. Progress Report of Studies of the Grating Type of Sand Trap Conducted at Bellvue and Fort Collins by Walter B. Leaf, Oct.-Dec. 1934," Irrigation Research Papers, Water Resources Archive, CSU Archives and Special Collections.