Walker - 1967 - A geography of Italy

SEAS AND COASTS
flattened to form a fringe of frontal spits. Largely as a result o f human interference
the delta north o f the Po Grande is moribund (at least at the moment)
and half its surface is occupied by imperfectly filled sacchi which are ignored by
the two weary distributaries ‘draining’ this part of the delta (Po di Levante, Po
di Maestra). Some 8o% o f the river’s discharge, which has been calculated to
include a detritus load o f 40 million tons per annum, passes through the Pila
and Tolle mouths j most o f the rest uses the Gnocca and Goro charmels. The
negligible gradient o f the distributaries makes land drainage by gravity almost
impossible and reclamation by poldering has had to contend with the further
lowering o f the surface by shrinkage. Furthermore, apart from the hazards o f
autunm flooding, this area, like most deltas, is sinking under its own increasing
weight and in recent years the pace o f collapse has quickened. It is feared that this
acceleration may be connected with the extraction o f methane; one zone fell
70 cm between 1951 and 1956.
South o f the modern delta, in Emilia, a somewhat different type o f alluvial
coast may be recognized. It consists very largely o f fossil deltas (classical and
medieval in age) whose seawards edges, never sharply prominent, have been
redistributed by waves and wind into a more or less continuous sweep of sandspits
and dunes. In classical times the most active distributaries o f the Po, each
with its rather flat delta, were what are now the upper Po di Goro, Po di Volano
and Po di Primaro (which passes Ferrara and wanders into the Valli di Comacchio).
T h e famous break at Ficarolo (1152) robbed the Po di Volano o f most of
its share of the Po waters, and the discharge o f the other Emilian rivers flowing
directly into the sea is quite small. Lines o f fossil dunes and sandspits (dossi)
sweeping round from Ravenna towards Chioggia mark stages in the development
of the classical and medieval deltas; they can be easily identified in the two large
expanses o f shallow brackish water sealed off from the sea by coastal drift, the
Valli di Comacchio and the Valli di Codigoro. The meandering causeways in
these sheets o f water (they cannot properly be called lakes or lagoons) are the
levees o f former distributaries. Ravenna, which stood on the southern side o f
the entrance to a commodious bay, and was Rome’s 'main naval base in these
waters, survived the insidious threat o f silting until the Byzantine era. The
diversion of the Reno roimd the Valli di Comacchio, which was planned in the
eighteenth century was only satisfactorily achieved in the 1920s. In this area the
heavy burden o f silt in the rivers has favoured colmate natural^- rather than
poldering as a means o f reclaiming land.
From Carrara to Cilento the Italian coast is characterized by a series o f shallow
sickle-shaped bays looped between headlands (Monte Massoncello, Argentario,
Circeo, etc.) many o f which were formerly islands. The smooth shoreline o f the
bays is mainly the work o f waves which from the Quaternary onwards have
built off-shore bars and spits; the headlands and islands provided convenient
anchors for these constructive features. The extensive areas o f water sealed off
* See page 40.
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