REPORT OF INVESTIGATIONS No. 48


 92

 96 S-- ---



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 RECORD USED- WATER LEVEL ON 51th, 0Ith, 151h,2Oth,25th AND END
 90 -- ---- OF EACH MONTH, JANUARY 1950 TO SEPTEMBER 1966
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 and Sept 1956 through Aug. 1958. Most of the estimated record

 84
 was below 76 5 ft. (especially during 1957) and therefore the
 duration curve is less accurate for this portion.



 0 10 20 30 40 50 60 70 O0 90 100
 PERCENT OF TIME INDICATED LAKE LEVEL WAS EQUALLED OR EXCEEDED
 Figure 3.-Stage-duration curve for Lake Jackson.

 case, only the data for complete years common to both of the
 involved stations were used.
 The graph indicates that yearly precipitation at the three
 stations is almost equal and that there is no appreciable long-term
 deviation between the stations. Thus, the average of rainfall at
 these three stations should be reasonably representative of that
 falling at Lake Jackson.

 EVAPORATION

 Evaporation from Lake Jackson has not been measured directly,
 but the yearly rate may be estimated with reasonable accuracy
 from measurements of evaporation from the United States Weather
 Bureau Class A Pan at Woodruff Dam (fig. 1). Records of pan
 evaporation for years 1959-65 are summarized in table 1.