Takaya et al. - 1974 - Rice cultivation and its environmental conditions

218 Y. TAKAYA, K. KYUMA, and K. KAWAGUCI!l
0 10 km
.........._.
~ Rt•claimPd sl'ction
0 Modern dt•lta
Q Jtidl!e swale compl .. x
0 Ancif'nt dt>lta
0 Water surfact•
An·•a in which rict• J{l'lJWing is common
M Town of Massa Fisca1dia
Fig. 4. A simplified l{comorphologic map of the Po Delta.
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Ancient Delta, which is believed to have been formed during and before the Roman
era, occupies the inlandmost portion of the delta. This has a very flat ground surface
whose ground height is in most places lower than 1m above se2 level. The sediments
consist of clay, sand, and peat. ~idge-Swale Complex is composed of silted-up lagoons
and old beach ridges with some overlying dunes. The dunes may attain as much as
6 m but averag-e :1 to 4 m in height. These are made exclusively of sand. Swales
between ridges also have sandy ground surface with some clay and peat lenses. Modern
Delta, which is supposed to have been formed after the Medieval age, has a beautiful
lobate shape and is a complex of numerous distributaries and interdistributary basins.
Distributaries have loamy levees and inter-distributary basins have, in most places,
clayey floors with local sandy spots. The area termed as Reclaimed Section is the area
which has been artificially reclaimed after the 1950's. Fill consists of clay and sand,
and profuse brackish shell fragments are occasionally found.
In Modern Delta, farm lands arc protected from flooding by strengthened natural
levees installed with pumps. In Ancient Delta and Reclaimed Section, where natural
creeks are not as numerous as in Modern Delta, many man-made canals, most of them
straight, arc dug to regulate the water.
Ancient Della and Modern Delta arc two main rice tracts, of which the former
lays more stress on sugar beet cultivation than on rice, whereas the latter is characterized
by more or less monocultural growing of rice.
II) Rice land of the Jherian Penit~sula
The Iberian rice lands arc scattered, forming small patches on varying environments
(Fig. 5). They arc on (1) Cuadalquivir marsh land (Sevilla), (2) inland valley near
Hadajoz (Hadajoz), C:i) Albufcra lagoon (Valencia), and (4) Ebro delta (Tarragona), all in
Spain; and on (5) Mondego valley (Coimbra), 16 & 7) Sado valley and its coastal dune
zone (Setubal), and (8) Tejo valley (Santarern & Lisboa) in Portugal.
/) Guada/quivir Marsh /.and
As shown in Fig. fi, the lowest reach of the Guadalquivir river forms a large marsh
land. ft is ca. 30x40km 2 , with maximum ground height of 3m above sea level. The
northern portion has riverine environment influenced by fresh water inflow from rivers.