Notes on morphological characters of ephemeral stream in Apulia region, South Italy

Murgia highland is the central part of Apulia region in South Italy, it is characterized by the absence of rivers and active flow lines, but the Mesozoic limestone platform is crossed by a complex system of ephemeral streams. They are locally named “lame” and are generally quite irregular. Locally they resemble river valleys not severely deep with a flat bottom, clear banks and well defined stream net. Anyway sometimes the morphological paths of their courses are not evident and quite discontinuous. Their catchments are normally highly permeable and even if they are considered watercourses, the water flow just occasionally occurs and they can be dry for several decades. They are so peculiar morphological elements that it has been considered quite interesting to analyze their main morphological characteristics. Their features are herein investigated focusing on a zone on the Adriatic coast north of Bari. Morphometric analyses of the study area were based on Digital Elevation Model (DEM) of Apulia (www.sit.puglia.it), resolution 8 m. The analysis shows that even if these streams develop on a Mesozoic bedrock, they can be considered in a transition stage between “young” and “mature” evolution. The analysis of azimuthal direction shows quite well defined preferential directions with a certain agreement with the main direction of fractures in the limestone substratum. These characteristics reasonably induce to believe that their genesis could not be ascribed only to erosive dynamics. In fact, the network is strongly conditioned by tectonics and their origin could be related to cracks of the carbonate bedrock induced during the tectonic uplift of Murgia platform. The morphological characteristics of Murgia ephemeral stream network are compared with those of the ephemeral streams located in the same climatic area (Brindisi Plateau), but in a different geological environment (quaternary deposits). The second network show hypsometric curves typical of “mature” streams, despite being set in more recent soils. Even in this case, the azimuthal stream direction analysis showed not casually distributed flow directions. The morphological analysis emphasizes that these streams are important morphological elements of the landscape to be protected, but even if they sometimes drain runoff, they cannot be considered as convention streams. This has a strong relevance in the evaluation of the flood risk related to their presence.