1.   Purpose and objectives

     Improving estimates of design flood, specified by return period, by the use of large historical floods.

2.   Description

     The magnitude and return period of historical floods are estimated and these estimates can be combined with conventionally recorded floods to give improved parameter estimates for the frequency distribution. The magnitude of the design flood, of a specified return period, can then be determined 
more reliably.

3.   Input

     The recorded annual maxima, one or more historical floods (see component H83.1.01), the typical flood hydrograph.

4.   Output

     The mean, coefficients of variation and skew of flood peaks, volumes and durations, together with the design flood values and the design flood hydrograph.

5.   Operational requirements and restrictions

     Twenty or more annual maxima, at least one historical flood.

6.   Form of presentation

     Manual describing the technique.

7.   Operational experience

     Has been used in China to give significant improvements in the reliability of design flood estimation and is now incorporated in the `Standard for computing design floods for hydraulic structures' approved by the Ministry of Water Conservancy and the Ministry of Electric Power.

8.   Originator and technical support

     Institute for Water Conservancy and Hydropower Research.

9.   Availability

     Through the HOMS National Reference Centre for China.

10.  Conditions on use

     Cost of reproduction and mailing.

REFERENCE:
Chen, Ye and Tan. The important role of historical floods in estimating spillway design floods Scientia Sinica vol. 18, no. 5 (Sept-Oct 1975).