To cite package 'weirs' in publications use:

Asquith W (2015). weirs—A hydraulics package to compute open-channel flow over weirs. R package version 0.25.

Corresponding BibTeX entry:

  @Manual{,
    title = {weirs---A hydraulics package to compute open-channel flow
      over weirs},
    author = {W.H. Asquith},
    year = {2015},
    note = {R package version 0.25},
  }