The river has distinct periods 

 of high and low flow each year. High 

 flow usually occurs from June through 

 October, and low flow from November 

 through May (Table 1). There is com- 

 monly an order of magnitude differ- 

 ence between low and high flow in a 

 given year. Even within low and high 

 flow periods, day-to-day flow varia- 

 tion can be large with respect to the 

 monthly or seasonal average flow. 

 This natural variation in flow pro- 

 duces large standard deviations asso- 

 ciated with monthly mean flows. For 

 example, the standard deviations as- 

 sociated with each monthly mean flow 

 during the period of record (1931- 

 1980) ranged from 74 percent to more 

 than 100 percent. 



During this five-year study 

 period, mean river flow was about 

 28 percent less than the mean for the 

 period of record (Table 1). Seasonal 

 pattern of the five-year mean flow 

 was not very different except for 

 late winter through early spring 

 (February-April) . 



Examination, for example, of the 

 wet season freshwater accumulation 

 data provides a means of classifying 

 each year (Figure 1). Two wet sea- 

 sons, 1975 and 1977, were drier than 

 the others. In 1979 most of the sea- 

 son (June through August) was drier 

 than average. However, flow in Sep- 

 tember was more than 2.6 times the 

 previous three months, resulting in a 

 seasonal flow ranked as wetter than 

 average (Table 2). Similar analyses 

 were done for the dry season (Figure 

 2). 



The use of specific mean flows 

 in comparison to the long-term means 

 may be misleading, especially if the 

 distribution of monthly flows is 

 skewed, as in the case with Peace 

 River flows. For example, the mean 

 flow for June is 32.3 m /s (Figure 

 3), but 73 percent of the obser- 



vations are less than the mean. Dry 

 season distributions as exemplified 

 by December plus January are similar- 

 ly skewed (Figure 4 and Table 1). 

 Wet season median flow for the period 

 of record accumulated by month was 

 about 25 percent less than the long- 

 term mean accumulation. The five 

 years of flow data during this study 

 generally fall on the low side of the 

 median as well as the mean for the 

 long-term frequency distribution. 

 Only July 1978, August 1978 and Sep- 

 tember 1979 exceed the long-term 

 monthly average for wet seasons 

 (Table 1). October 1979, November 

 1975, December 1977, January 1978 and 

 1979, February 1978, March 1978, 

 April 1980, and May 1978, 1979, 1980 

 exceed the long-term average. 



Cyclical patterns in both the 

 wet and dry season flows appear to 

 occur over a 5 to 8 year period (Fig- 

 ures 5 and 6) and average about 6 

 years. These longer term changes in 

 flow are variable. However, since 

 the high flow peaks in 1959-1960, wet 

 season changes have been much less 

 than those before 1959-60. The high 

 flow peaks in the dry season have 

 been relatively low since the last 

 high peak in 1970. 



Cyclical patterns have been found 

 by Shih (1975), for water levels in 

 Lake Okeechobee and the Kissimmee 

 River, and by Meeter et al. (1979), 

 for the flow of the Apalachicola 

 River. These oscillations are varia- 

 ble but tend to repeat at intervals 

 of 5 to 7 years. 



The fish data reported here 

 coincide with low points for both 

 the wet and dry seasons and for 

 ascending trends. However, the high- 

 er flows are much less then during 

 other intervals. 



298 



