The Agliena torrent and its weirs

Along the course of the torrent Agliena there is a naturalistic area which is very interesting both for the presence of plants and animals and for the number of easily identifiable fossils on the slopes where pliocene sands and clays are subject to pluvial erosion.
It is easy to walk along a great part of this watercourse thanks to a footpath maintained by the Consorzio di Bonifica 3 Medio Valdarno.  However, the most important feature is the great number of weirs most of which are probably of medieval origin. These have been restored recently and are an exceptional example of the knowledge of hydraulic techniques in the past. The torrential course of the river is marked by these weirs which reduce the speed of the flow and the transport of solid matter.
In a map drawn by Leonardo the toponym Agliena (Ghienna) is recorded.
Leonardo perfectly described the function of these weirs across the flow of the river.
“The dams of rivers that are not of too great width should be made in this manner: a stake such as pile drivers use should be fixed every three braccia, as big as possible and the bigger the better; and their tops should be of uniform height. On these a log of the shape of a beam should be fastened heavy very firmly; next, long trunks with all their branches should be taken and laid upon the aforesaid beam, and they should be fastened to it by using one of the branche sas a hook; and this process should be repeated as often as possible, placing the branches toward the coming toward the coming of the water; and they should then be loaded with shingle and stones; and after the first flood it is left grounded…” (Codice Leicester, c 27v)
The whole course of the Agliena is 8 km long and is easy to walk, especially between the late spring and the first months of the autumn.