Miscellaneous study reports and questionnaires, Ychwanegu i'r clipfwrdd 3. Ffeil 1983-1984. Rhan oPlaid Cymru: Hydro Group Papers,
Constitution and rules of the Hydro Group; minutes of Hydro Group meetings, Ychwanegu i'r clipfwrdd 1. Ffeil 1983-1986. Rhan oPlaid Cymru: Hydro Group Papers,
General correspondence relating to the Hydro Group, 1983-1986; copies of Tonnau/Waves, the Hydro Group newsletter, 1984-1986, Ychwanegu i'r clipfwrdd 2. Ffeil 1983-1986. Rhan oPlaid Cymru: Hydro Group Papers,