The present study evaluates selected morphometric characteristics of 39 direct tributaries of the Buzău River (area of 4112 km²) to prioritize development actions in these sub-watersheds, which are distributed in three geographical regions within the full Buzău River watershed: the Carpathian, Subcarpathian, and plains regions. By combining a variable number of morphometric parameters, using various mathematical models, we can evaluate the state of balance or imbalance in a watershed and identify sub-watersheds vulnerable to natural processes. Prioritization was achieved using composite (Cp) values by comparing two scenarios. In the first scenario, 11 derived morphometric parameters were used, and in the second scenario, another 7 parameters were added. The obtained values were grouped into five classes (very high, high, medium, low, and very low). Due to the heterogeneity of relief units among geographical regions, there are classification differences for sub-watersheds among those regions. Watersheds classed as very high priority for intervention actions are located in the Carpathian (SW1, SW2, SW15, SW16) and Subcarpathian areas (SW24, SW30), which are characterized by high relief energy and pronounced slope instability, which leads to an increase in the risk of flooding and land degradation. For comparison, all sub-watersheds in the plains region, are classified as very low or low priority. Since the arithmetic mean is sensitive to extreme values, its use in the calculation of composite (Cp) values causes the values to be “eclipsed” and the sub-watersheds to be placed in different prioritization classes (SW18 and SW34), depending on the analyzed scenario, due to the large number of parameters and classified sub-watersheds.

Soil loss due to erosion is a form of land degradation, having significant effects on agricultural productivity, water resource quality, and food security. The morphometric analysis of the drainage network is based on mathematical relationships and geometric progressions. In previous studies, several morphometric parameters have been analyzed in relation to stream order. While numerous studies have assessed soil loss at the watershed level, its spatial variability at the sub-watershed level remains less understood, even though it can highlight sectors that disproportionately contribute to soil loss. Thus, this study aims to analyze whether the RUSLE-estimated soil loss values follow the same morphometric relationship and geometric progressions by examining the hierarchical distribution of soil loss in the 39 sub-watersheds of the Buzău River Basin. The methodology consisted of extracting the mean and summed values of soil loss from the RUSLE2015 raster for all 9369 sub-watersheds, which were hierarchized into seven orders of streams. We created two laws of summed and mean soil loss, and the law of the number of sub-watersheds corresponds to the law of the number of segments. The three data series exhibit geometric progression patterns for which ratios have been calculated. Internal variations in the estimated soil loss have been observed. The sub-Carpathian sector is the most susceptible to the estimated mean (66%) and total (73%) soil loss. Sub-watersheds whose area is smaller or comparable with that of other sub-watersheds in the Carpathian sector exhibited much higher soil loss values (SW 11- 0.16 t ha⁻¹ yr⁻¹ vs. SW 33- 3.36 t ha⁻¹ yr⁻¹). The Slănic sub-Watershed loses a total of 202,325.48 t yr⁻¹, while Bâsca loses only 50,573.86 t yr⁻¹, even though its area is much larger (78,300 ha). The highest values of mean soil loss are recorded in Oleșești, at 9.19 t ha⁻¹ yr⁻¹. These results can support authorities in identifying and prioritizing sub-watersheds that may require soil conservation measures and can be reproduced in watersheds with different characteristics.

Geographical studies and environment protection research