166 
waters is accompanied by a considerable increase in their 
plankton. This fact, combined with the increase in the vol- 
ume of their contributions due to higher levels, augments the 
relative importance of their share in the formation of the river 
plankton, tending to increase its quantity and variety. On the 
other hand, the repetition of floods, no less than eight of which 
may be found in the hydrograph, flushes the river so often that 
no concentration of sewage and marked maximum of plankton 
occur. The unusual extent of these movements is apparent 
when the total movement for the year, 50.7 feet, is compared 
with the totals of other years having about the same average 
height. For example, 1890 and 1897, with an average height 
of 6.9 feet, have a total movement of only 44.2 and 36.56 feet 
respectively. In brief, the year was one without extended 
overflow, with lower water than usual at the normal flood sea- 
son, with prolonged bank-full river and reservoir action of the 
permanent backwaters, and with more than the usual turmoil, 
In 1897 we find a hydrograph (Pl. XI.) which approaches 
the mean closely in its main features, and exhibits all the ex- 
pected movements excepting the equinoctial rise. The average 
height for the year, 6.90 (6.86 at Copperas Creek), is also near 
the general average (6.74). The year thus approximates the 
normal. The high-water period is of 141 days’ duration, al- 
most exactly the average (140), but it occurs somewhat earlier 
in the year and attains 16 feet—a little more than the usual 
height. The earlier decline renders more prominent the June 
rise, and gives an early start to the extreme and uninterrupted 
low water of the remaining five months of the year. The low- 
water period (155 days) is normally located but is somewhat in 
excess of the average (147), and it is also unusual in the fact 
that the extreme low-water level (1.7 feet since the completion 
of the dam at LaGrange) continued almost unchanged from 
the middle of August till the first of November. This was fol- 
lowed by the usual slight increase in water in the closing 
months of the year. The total movement of the year (43.1 
feet) 1s considerable in view of the average height (6.9 feet), 
