Suggested citation for smwrBase:

  Lorenz, D.L., 2015, smwrBase---An R Package for Managing Hydrologic
  Data, Version 1.1.1: U.S. Geological Survey Open-File Report
  2015-1202, 7 p.

A BibTeX entry for LaTeX users is

  @TechReport{,
    title = {smwrBase--An R Package for Managing Hydrologic Data, Version 1.1.1},
    author = {David L. Lorenz},
    institution = {U.S. Geological Survey},
    series = {Open-File Report 2015-1202},
    year = {2015},
    pages = {7},
    url = {https://pubs.er.usgs.gov/publication/ofr20151202},
  }