In Puglia they define themselves blades the shallow erosive furrows, typical of the landscape Apulian, which convey the rainwater fromMurgia plateau towards the closing point of the drainage basin which they belong. The terminal sections of the blades are also called blades ravines, a term which instead designates deep incisions with steep banks
The blades are usually confused with generic streams. The difference between a blade and a stream is substantial, since in the blades, due to the high porosity of the soil, the surface circulation is small, while it is prevalent in the subsoil. Furthermore, the blades carry water only at rain events, collecting the waters of the drainage basin to which they belong, while they are substantially dry in normal periods.
Source: Wikipedia
Therefore, the blades are not very developed incisions, with a flat and flared bottom and together with the ravines they constitute the main valley elements of the karst landscape and, during rainy events, they collect the surface runoff of the water.
Usually these impluvia are devoid of water due to the high permeability of the rocks of the carbonate substrate due to the presence of widespread fracturing systems and karst conduits. Due to the aforementioned characteristics, the basins of the blades are not very hierarchical, discontinuous and generally torrential.
Curiosity. They are called blades precisely because seen from above (through aerial photographs or drones) you can see real engravings of the soil and the geometries of the terrain.
The example of the blades of the Castellana caves
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Adventure Tourism in Apulia: “the blades” of the territory.
Adventure Tourism in Puglia: the "blades" of the Territory
The blades recognizable in the surroundings of the Castellana Caves develop mainly in SW-NE and NW-SE directions, secondarily in the NS direction: the larger ones, in particular, belong to the first orientation system and receive contributions from the second system from both sides. The largest blade is the one which, starting from Cupa, heads towards Castellana and joins other erosive furrows coming from the Spirito Santo, to then flow into the main blade which heads towards Largo Porta Grande, the most depressed point of the karst basin of Castellana. It is in fact here that in the past, on the occasion of major meteoric events, floods have repeatedly occurred, even disastrous and with numerous victims, as in the case of November 1896.
Yet, as in most of the Murgia area, the recognition of epigean morphologies is today quite difficult even in the Castellana area, due to a series of human activities that are causing a strong degradation of the Apulian karst, sometimes up to the cancellation of the typical forms of this karst landscape. Intense phenomena of stone removal, filling of morphological depressions and karst cavities, quarrying activities (in some cases abusive), repeated cases of pollution both on the surface and of the underground aquifer, are unfortunately the order of the day in Puglia, and produce direct effects, sometimes irreparable, on the karst landscape.
Importance of "blades"
The blades are characterized by alluvial soils formed over time, very fertile, as opposed to the calcareous rocky soils typical of the Murgia area. For these reasons, and for the presence of water, since neolithic the blades have been home to human settlements.
The existence of the blades is due precisely to karst of the Puglia region. The heavily fractured limestones of the Murge they appear to be very permeable to rainwater (the limestone itself is impermeable, but if strongly fractured, it becomes very permeable). The permeability of the region means that the water circulates in a small part on the surface and mostly in the subsoil. In the blades the water also circulates on the surface, but the percentage of water that circulates in the subsoil prevails and which, horizontally, follows almost the same path as the blade. This is due to the capillary effect (capillary fringe).
The blades also play an important role in hydraulic functionality and at the same time are valuable naturalistic environments, ecological corridors that connect different ecosystems, from the Murgia to the sea. The karst network brings high biodiversity habitats close to urban contexts, sometimes crossing them.
Tourism and "blades"
Precisely because of their exceptional presence on the Apulian soils, due to the also rare karst phenomenon, the blades have been the ideal place for anthropization and ideal routes for moving or trading in Antiquity. Flanking many ravines in past centuries they were ideal sheep tracks, ready for use and no less important deposits of fertile land suitable for intensive cultivation.
Along the walls of the blades, moreover, are frequent cave settlements excavated in soft limestone.
Of notable interest is the rock church of Santa Candida the most important example of the rock phenomenon in the territory of Bari. There church of Santa Candida, obtained on the right side of the Picone blade, dates back to the 9th-10th century and is mentioned in Barese Diplomatic Code of the 1192.
The blades of the systems of the Gravine di Mottola, Laterza and of Matera itself have complex systems of branching and organization and are clearly visible after large rainfall events. The Rupestrian Churches, for example, of these three large complexes of ravines it is good to remember the innumerable Rupestrian Churches and urban furnishings suitable for collecting the precious rainwater.
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