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I I I I I I I I I .. I I I I I I I I I 003:58 water supply to a nearby City and the City wishes to estimate the 10-year average flow and 10-year low flow. Examination of those records with concurrent data indicates that the streamflow in Stream 41 is always equal to 20 times the measured rainfall; similarily, the streamflow in Stream #2 is always equal to 5 times the measured rainfall, or 25 percent of the streamflow in Stream #2. Using these relationships, the missing years of data for Stream #2 can be determined as follows: 0 For year #1, streamflow #2 0.25 x streamflow #1 0.25 x 200 = 50 ac-ft 0 For year #2, streamflow #2 0.25 x streamflow #1 0.25 x 300 75 ac-ft 0 For year #8, streamflow #2 = 5 x precipitation 5 x 20 100 ac-ft 0 For year #9, streamflow #2 = 5 x precipitation = 5 x 5 25 ac-ft In this way, the historic streamflow record can be extended over a longer period to provide important information. In this example, for instance, the procedure used above showed that the streamflow in year #9 for stream #2 was only 25 ac-ft. If only the data available from the direct measurements at stream #2 had been considered the actual flow during year #9 would remain unknown and the minimum flow would appear to be 75 ac-ft. Use of this procedure is referred to as "augmentation" of a historic record. It is also possible to use statistical and stochastic techniques to generate a much longer (many hundreds or thousands of years) period of record than is historically available. These techniques rely on examining the serial (i.e., year-to-year or month-to-month) relationships evident in an existing historic record in conjunction with annual (and/or monthly) average and extreme values. This procedure is called "generation of synthetic streamflow". Both augmentation and synthetic generation 4-2