1”Babeş-Bolyai” University, Faculty of Environmental Science, 400327, Cluj-Napoca, Romania, e-mail:
ABSTRACT. – The Law of the Order of Watersheds. In fluvial geomorphology studies that aim at deciphering the evolution of landforms, apart from the identification of the order of streams, it is also very useful to know the order of the watersheds. The main purpose of this paper is to formulate the law of the order of watersheds. It also checks if the stream order and the nearby watershed order have the same value. In order to highlight this, a methodology has been established in order to formulate the abovementioned law. As a starting point, we used the order of the streams law, in Horton-Strahler system, in the form used by Zăvoianu in 1978. An analogy between them was established, in the sense that the node rate or the watereshed intersection rate was used instead of the confluence rate, because watersheds do not form a confluence, but gather into orographic nodes. In order to verify this law, 12 watershed models have been selected from the autochtonous drainage systems, representative for the Transylvanian Basin. The acquired results demonstrate on one hand that the law is valid, and on the other hand that it is not necessary that streams and bordering watersheds have the same order. This fact is possible because the difference between the order of a major watershed and of the bordering main streams also presents variations. In most of the cases, the order of the watershed is higher than the one of the neighbouring streams. The difference recorded in these cases increases as the number of lower order streams do not form confluences, in order to increase the drainage system order, but they flow directly into an upper order mainstem, whose order cannot be increased.
Keywords: watershed, node rate, order, drainage network.