400 



both localities (cf. PI. IX. and XXXVI.) in the face of these 

 contrasts in amplitude. 



1896. 

 (Table VIII., PL XXXVII.) 



There were 27 collections in this year, at monthly inter- 

 vals until April, and then every 5-11 days until the end of Au- 

 gust, and thereafter every fortnight. The average production 

 in this year is 9 cm. 3 per m. s , with a maximum at the vernal 

 pulse on May 2 of 48.99 cm. 3 



The hydrographic conditions of this year are such as to 

 bring Thompson's Lake into intimate connection with chan- 

 nel waters. The average height of the river for the year, 6.98 

 ft., is sufficient to maintain a run off from the southern end of 

 the lake to the river, submerging the bottom-lands between to 

 the depth of a foot. Indeed a run-off of varying depths was 

 maintained for 241 days, in which stages exceeded 6 ft. This 

 was due to the recurrence of 6 floods, so distributed as to keep 

 the lake discharging through the southern outlet for 241 days 

 with only 5 interruptions between May and December. Of the 

 125 days in which water did not flow through the lake from the 

 northern to the southern end, there were 29 of rising water in 

 which no discharge to the river occurred, 28 of stationary 

 levels in which the movement of the water, if any, was declin- 

 ing, and 68 of falling water, in which the lake discharged 

 through the slough at the northern end. Thus, during 309 days 

 of the year this lake was discharging to the channel, waters 

 which had been impounded for a varying length of time within 

 its boundaries. The importance of this impounding area is 

 best shown by rough calculations which show that the run-off 

 of a single foot from the lake proper, not including the expand- 

 ing areas which join it with every rise in levels, will fill the 

 channel of the river at Havana to a depth of 8 ft. (low-water 

 stage) for about three miles. In 1896 the total depth of the 

 run-off for the year computed on a single discharge after each 



