464 



ton-rich channel water, or its partial replacement by the plank- 

 ton-poor and silt-laden flood. Typical illustrations of its action 

 appear in the planktograph of 1896. 



The rising stages of the flood are the most disastrous. They 

 carry the heaviest burden of silt, are formed of the most recent 

 water, and usually, because of their sudden inroads, most com- 

 pletely replace the previous channel contents. The December 

 flood of 1895 is a typical illustration. Rising suddenly from 

 low levels (3 ft.) to overflow stage (12.6 ft.) in 12 days, it de- 

 pletes the channel plankton from 2.6 cm^ in the initial stages 

 of the flood on the 20th (PL IX.) to .08 on the 25th, if not, in- 

 deed, earlier. Not only does it thus depress plankton content 

 in channel waters but, with a less catastrophic completeness, 

 that also in the backwaters. Thus in Thompson's Lake the 

 plankton falls from 1.87 cm.' on the 19th to .13 on the 28th, 

 in Quiver and Dogfish lakes, from .63 and 10.57 to .29 and 

 .06, and in Flag Lake, from 6.38 to 3.26. The effectiveness of 

 the depletion is greatest where overflow currents are best es- 

 tablished, as in Thompson's and Dogfish lakes, and least where 

 the currents are slight and impounding greatest, as in Flag 

 Lake. 



With the culmination of the flood the proportions of in- 

 coming storm water of recent origin decline rapidly, the effects 

 of the run-off of impouuded backwaters begin to appear, and 

 recovery in production, other things being equal, marks this 

 stage of the flood. Typical illustrations will be found in the 

 June and August floods of 1896 (PI. X.) and in the June flood 

 of 1897 (PI. XL) and 1898 (PI. XIL). 



The results of flood in the backwaters are similar to those 

 in the channel wherever currents of overflow are established 

 and replacement of the plankton-rich contents of the lake by 

 flood waters ensues, as has just been shown. Usually there are 

 accessory bottom-lands, not swept by current, where a part of 

 the original lake waters are retained, and where plankton 

 breeds abundantly. As a result of this, the recovery from the 

 depletion by flood — and this is usually not so complete as in 



