'Field notes: Mesopotamia. General Staff, India. February, 1917.' [‎34r] (74/350)

The actual positions of lakes are occasionally greatly affected
by the direction and force of the wind. Certain lakes have
been observed to extend on one side or contract on the other
.for as much as one or two miles when a strong wind from the
North has succeeded a strong wind from the South. These
changes do not take place gradually either; in one case the
edge of a lake approached a camp at a rate of between 12 and
15 yards a minute and necessitated a rapid change of site.
Troops may encamp at night on good dry ground with little
or no water in sight and yet find by daybreak that a broken
bund, a shifting lake, or the effects of seepage have made it
impossible to stir from the camp, which may itself be under
water. Indeed so great is the risk of unpleasant surprises,
and so deep the mud at times, that causeways some miles
in length have sometimes to be built. Along them, troops,
guns and transport move in the direction required, and when
they reach their journey’s end the camps they occupy, or the
trenches they man, must often be surrounded by dams or other
earthworks if they wish to be reasonably sure of not being
flooded out before the morning.
All these difficulties are at their maximum during the period
of high flood at which time the movement of troops near marsh
or river is fraught with considerable risk. Also the flood-
period comes at an unfortunate time of the year. If there
were no floods in March, April and May, these months would
be the best for military operations; the weather is then better
than at any other time, there is little rain, and a reasonable
temperature prevails, but these climatic advantages are entirely
nullified by the floods whose subsidence is followed immediately
by the burning heat of June, July and August.
Beyond the marsh and lake areas lie stretches of desert
which are, generally speaking, unflooded, and passable but
waterless. In the East the desert extends from the edge of
the marshes to the Pusht-i-Ivuh, but here it is liable in parts
to be inundated by the overflow from the Abi Gunjian Chun
and from the mountain-streams when the snows are melting
during March and April. West of the Tigris the desert similarly
begins at the edge of the marshes some 20 miles from the river
and extends until it merges in the marsh area watered by the
Hai and its Eastern—or left bank—distributaries. West of
the Hai the process is repeated towards the Euphrates, so that
speaking in broad terms, there is always the same sequence of