THE TERASSPERE - A PROPOSED SI UNIT FOR THE FREQUENCY OF RECURRENCE OF A HYDROLOGICAL EVENT

In seeking to use SI units in accordance with British policy as laid down by Act of Parliament, the author has devised a new SI unit for the frequency of occurrence of a hydrological event (flood). The derivation of the unit from the six (later seven) base SI units is given. It is shown that every 996 000 000 000 000'th second the annual event occurs with a frequency of 1 hertz. This is within 0.4 percent of 1 000 million million seconds per hertz, or 1 000 million million seconds squared per cycle. In other words it is a 1 000 terasspere event. This is well within the inherent errors of statistical methods. Thus the event which occurs on average once in 1000 years would have a terasspere value of unity. The SI unit for daily would be 365 000 Ts-squared, weekly 52 000 Ts-squared, and monthly 12 000 Ts-squared. It is a matter for discussion whether a special name might be given to the 1000 terasspere, or annual, value. The unit has the advantage that the value increases directly the more often the occurrence, instead of the inverse relationship encountered within the use of return period. The value in the derived SI unit is numerically equal to one thousand divided by the return period in years. The 50 year flood is a 20 terasspere flood. /AUthor/

  • Corporate Authors:

    International Association of Hydrological Sciences

    Institute of Hydrology, 1909 K Street, NW
    Washington, DC  USA  20006
  • Authors:
    • Baty, M F
  • Publication Date: 1975-3

Media Info

  • Features: References;
  • Pagination: p. 47-50
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00127218
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 14 1976 12:00AM