Laserfiche WebLink
<br />12 <br /> <br />Probability of recurrence of low flows <br />flows (V. S. share) at Falcon shows a variation from a minimum of 444,000 to a <br /> <br />The Rio Grande record of annual <br /> <br />maximum of 4,025,000 acre-feet during the 1900-64 period. Law flows will occur, <br /> <br />and it is desirable to know the probability of a low annual flow occurring in any <br /> <br />one year; this information will allow evaluation of the risk taken by assuming <br /> <br />availability of certain flows. <br /> <br />It has been shown that the flow for period before 1945 may be greater than <br /> <br />it would be with today's development. If so, the frequency curves based on the <br /> <br />1900-64 period show 'too much water. Computations were made, as described below <br /> <br />in items 1-7, using "records" for both the 1960-64 and the 1945-64 period. <br /> <br />The probability of recurrence, or chance of occurrence, of annual. flows of <br /> <br />selected amounts have been computed as follows: <br /> <br />1. Annual, discharges were listed for each year (columns 1 and 2, <br /> <br />tables 9 and 10). <br /> <br />2. Rank, m, of each annual event was recorded, the lowest flow being <br /> <br />ranked 1, the second lowest ranked 2, etc. (col. 3, tables 9 and 10). <br /> <br />3. Recurrence interval, T, of each event was computed as T = (n + l)/m, <br /> <br />where n is number of years of record (col. 4, tables 9 and 10). This <br /> <br />is a standard method for evaluating probabilities. <br /> <br />4. Discharges vs recurrence intervals were plotted on a special form <br /> <br />designed for this purpose and a curve for each time period was drawn <br /> <br />through the plotted points (see figure 5, p. 42). <br /> <br />5. Annual flows for selected recurrence intervals read from curve of <br /> <br />figure 5 were listed in table 11. <br /> <br />6. The p(:,rcent chance of occurrence of flows are listed in last column <br /> <br />of table 11. The smallest annual flow listed has a recurrence inter- <br /> <br />val of 100 years; this means that a flow this small or smaller will <br /> <br />recur on the average once in 100 years. As the event may recur once <br /> <br />,~, ,': rr (" >- ,>1 <br />',_.'..... t....... \J 0 <br /> <br />in 100 years its chance of occurring in any one year is 1 in 100, or <br />