STRUCTURE AND HISTORY OF PLAV. 239 
relation of the various Balta-lakes to the river water-supply may be given. 
to illustrate how circulation is effected. 
The Balta-lakes stand roughly in three relations to the river water-supply. 
The lake-bottoms are situated either above, below, or about level with the 
local minimum water-level of the Danube. The normal height of the water- 
surface of the lakes is approximately 1 m. (about 3 feet 3 inches) above the 
lake-bottom (Dr. Antipa’s conventional lake-surface); the Danube has 
therefore to reach at least the height of the lake-bottom plus approximately 
1 m. in order that water may pass by the gérlas to the lakes, and a 
greater height in order to flow over its own embankment and those of the 
lakes. 
(1) Between the Rumanian frontier and the mouth of the river Prutu 
[Prut] near Galati [Galats], the bottoms of the lakes are about 0'8 m. to 
2-41 m. (about 2 feet 7 inches to about 8 feet) above minimum water-level 
of the Danube, and the Danube has to rise between 4 and 4:98 m. (about 
14 to 10 feet) before the waters are able to overflow the lake-embankments 
of that section. (2) Between the mouth of the Prutu and Tulcea the lakes 
are about 0-4 to 0-6 m. (about 1 foot 4 inches to 2 feet) under zero of the 
Danube, and the river has to rise about 2:2 m. (about 7 feet 2 inches), 
before it can flow over the lake-banks. (3) The delta lakes lie 1°8 to 
2-75 m. (about 6 to 9 feet) under zero of the Black Sea (2. e. —1°8 to 
—2-15 m.), that is to say at least 2 to 2:2 m. (about 6 feet 64 inches to 
7 feet 2 inches) below minimum water-level of the Danube. The river does 
not, however, flow over their banks until it has reached a height of about 
2:18 m. (about 8 feet 9 inches) at Tulcea. 
The heights of the lowest portion of the lake-banks and of the channel- 
shoals, as well as of the water-surface of the lake, in relation to that of 
the river, are factors which regulate inflow and outflow. It is, in fact, 
on the lesser physiographical features, such as channel-shoals, that the 
permanency of the Balta-lakes during low-water is often ultimately 
dependent. Dr. Antipa gives tables * showing the relation of the more 
important lakes to the river water-supply, indicating in most cases the 
height of the lake-bank, and also the height of the Danube at which the 
gárlas begin to function as inflow channels. Numerous diagrams in the text 
elucidate these relations. 
The river affects not only the Balta but also the Black Sea, whereas the 
latter, for its part, since it is tideless, affects the river but little : only very 
occasionally does salt-water pass up the Danube, and then only for a short 
distance, whereas the waters of the Black Sea close to land are diminished 
in salinity and are always more or less murky with silt from the Danube. 
There is, in fact, a visible line of junction often as much as 12 to 14 kilo- 
* See Antipa, “ Das Überschwemmungsgebiet der Unteren Donau," pp. 28-31 and 36-39. 
