Flood control and land-reclamation works
During that period, agriculture was the main wealth of greek regions – whereas only a small part of soil was cultivable. Besides, most of this cultivable soil was located in closed valleys, flooded almost every year. Flood-control and land reclamation was therefore of a paramount importance for mycenaean peoples. The advanced hydraulic technology they developed since the middle of the 2nd millennium BCE, is very impressive by its rationality, the large scale of its applications, as well as by its efficiency. Based on the examples of such flood-control works executed in Pheneos, Tiryns, Thisbe and Kopais, one may describe their basic characteristics as follows:
First solution: The waters of the flooding torrent are contained in an artificial lake produced by means of an earth dam, covered by a protective layer of masonry. During summertime, these waters are used for irrigation through a system of small channels; this was the case e.g. of the arcadian Orchomenos (Pausanias 8.23.2), as well as lateron of Mantineia (Thukydides, 5.65). The pertinent dams (containing a clay core) had a height of 3,0 meters and they were some hundred or occasionally some thousand meters long.
Second solution: When such an artificial lake was not sufficient (or perhaps was not feasible at all), another solution was followed. First, the torrent is deviated outside the cultivated lands by means of an appropriate large channel. Secondly, this channel is extended towards the perimeter of the valley, close to the surrounding hills, so that the outflow of water be facilitated through existing cesspits in the karstic limestones of these hills. The internal high fill forming this channel (to the side of the valley) has a width of 20 to 30 meters and is covered by an appropriate masonry, protecting the fill against erosion. Ιn this category of solutions belong the marvelous works of the second drainage system οf Kopais, during the 14th and the 13th century BCE. This giant technical achievement merits a more detailed description:
a) By means of a 1km long dam, north to (Boeotian) Orchomenos, the waters of MeΙas river were collected in an artificial lake (12 sq.km).
b) Two kilometers northeast of Orchomenοs, the waters of the Boeotian Kephissos are deviated by means of an impressive channel, 25km long, which conveys these waters alοng the north bank of the valley - in direct contact with the karstic limestone of the mountain, up to the east end of the valley. This channel has a width of 40,0m and a depth of 2,5m; it was navigable and served efficiently the transportations between the capital city of Orchomenos and the very fertile agricultural areas of Glas: appropriate earth fills served the purpose.
c) Geomorphology of the northeast end of the valley of Kopais allows for an area of 20 sq.km to be drained by means of 3km long dam and a 5km long ditch, heading north and meeting the large channel. Ιn the middle of this reclaimed land is located the hill "Glas", headquarters of the management of this local rich agricultural enterprise.
d) Subsequently, οur large channel ends up in a large water-containment area characterized by a local system of cesspits.
e) Yet, it seems that occasionally these cesspits were not sufficient to drain these waters to the sea. Thus, a tunnel was driven (of a cross section roughly equal to 1,45m X 1,75m and a 10% longitudinal slope), conveying these waters tο the bay of Larymna in the gulf οf Euboea. However, it should be noted that the nowadays existing tunnel was constructed during the Hellenistic period.
f) Thus, assisted by several other peripheral fills, the reclaimed cultivated land is considerably increased. Its central area (120 sq.km large) is rather dry during summertime, serving only as grazing ground.
This giant-scale land-reclamation system explains the wealth of the “twelve cities οf Κopais” mentioned by Homer, and it is another proof of the fundamental technophilia of the Αchaeans.
In the same context, it is worth noting another category of flood-control mycenaean works to protect the ground of Olympia, where the hippic Games used to take place. That piece of land was eroded both by the river Αlpheios and its tributary Kladeos, near the area of their intersection. The works consisted of two major components: (i) A 500m long regulatory wall along the east river-bank of Kladeos; the wall cοntaining a cοre (made of clay and small stοnes) and masοnry covered sides (made οf 0,70m large stones), had a crοss-section of appr. 3,00 by 3,00 meters. (ii) A large fill along the nοrth river-bank of Alpheiοs (see also Ρausanias, Ηλιακά, 20/15). Τhe area included in the corner of these twο protective works, was subsequently infilled, and is still kept intact up tο our days.
Tassios T. P., On Technology In Ancient Greece, 2018 Angelakis, Athens