114 EKMAN. ON DEAD-WATER, [norw. POL. EXP. 



sea. According to Penck 1 estuaries are essentially of three kinds, which 

 he calls bar estuaries ("Barrenmiindungen") funnel estuaries ("Mi'indungs- 

 trichter"), and deltas. The funnel estuaries are formed hy strong tidal currents 

 which wash away the ground as far up the river as they reach. The 

 quantities of sea-water flowing up and down, at flood and ebb, in these 

 estuaries, are many times greater than the river-water carried by the river 

 itself. In very large and full rivers, the river-current is not stopped by the 

 rising tide, and the flood-current runs in as an under-current; if the river carries 

 less water, the direction of the current in the estuary, is determined by the 

 tide. In either case, the river-water and sea-water mix and give brackish 

 water in the estuary (Penck p. 501). Such places are obviously not favour- 

 able for the formation of dead-water. The tides have not had the same 

 erosive effect upon the two other kinds of river-mouths, which are instead 

 formed by the erosive or sedimentary effects of the river-water itself. The 

 channel must consequently be entirely filled up by the river-water; and the 

 particles carried with it, either settle down directly on the bottom or are 

 carried in again from the sea by an under-current of salt-water, to form a bar 

 which silts up the mouth. The river consequently falls directly into deep water. 

 If the mouth is on a straight coast or at a cape, there may often be no 

 conditions favourable for the formation of dead-water, for in such a case the 

 river-water may be either carried off by currents, or the water-layers may be 

 mixed as an effect of ocean waves. Only when the river falls into a deeper 

 estuary or cove, will its water have an opportunity of spreading out over the 

 sea as a distinct layer of gradually decreasing depth ; and at such a place 

 dead-water is most likely to occur. [This is the case for example with 

 Congo River and Outa River.] Even in such places, however, little or no 

 dead-water will be felt, if they are navigated chiefly by steamers, or by 

 vessels of a draught much greater or much smaller than the depth of the 

 surface layer. 



In conclusion there are several circumstances necessary, to make the 

 conditions for dead-water really good ; and at a large number of river-mouths 

 these conditions are obviously not fulfilled. 



1 Dr. Albrecht Penck. Morphologie der Ei-doberflilche. Stuttgart 1894. Zweiter Teil. 

 P. 497 seq. 



