CRITICAL POINT and EQUILIBRIUM POINT

These points are located upstream (the former) and downstream (the latter).

The CRITICAL POINT marks the beginning of erosive processes linked to surface runoff due to reaching an optimal energy condition, while the second, the EQUILIBRIUM POINT, on the contrary, marks their cessation due to the loss of this optimal energy condition.

This aspect is extremely important as it highlights that both points characterize a transition from erosive processes to other types of processes.

Furthermore, it is possible to represent both in a summary graphical solution in terms of hypsometric and/or hypsographic coordinates, especially in terms of REAL ELEVATIONS, thus making a comparison between them possible.

Indeed, both of these points are defined by hypsometric and hypsographic coordinates and are therefore associated with very specific elevations, known as the ELEVATION of the CRITICAL POINT upstream, and the ELEVATION of the EQUILIBRIUM POINT downstream.

In the proposed model, both, when appropriately placed along a hypsometric curve, precisely identify (when present) the portion of the represented hydrographic basin within which erosive processes linked to surface water currents act.

In this conceptual model, this portion of the territory coincides with an "ACTIVE" ALTIMETRIC BAND.

Generally, the CRITICAL POINT is always present.

When the downstream point, or EQUILIBRIUM POINT, is not present, the entire slope downstream of the critical point is considered to be undergoing erosion.

The CRITICAL POINT is identified by first constructing the "Frequency Distribution Curve," hereafter "FDC" ("GULLY EROSION DEVELOPMENT IN DRAINAGE BASINS: A NEW MORPHOMETRIC APPROACH"; 2024 Ugo Ciccolini, Margherita Bufalini, Marco Materazzi, Francesco Dramis).

This is understood as the curve describing the layout of the hydrographic network, including its hierarchy, along the elevation or vertical direction.

In the proposed model, the CRITICAL POINT is defined by the ELEVATION at which third-order streams, or more generally GULLIES, begin to appear.

In this model, first and second-order streams are considered ephemeral and not representative of an establishing hydrographic network.

Conversely, the EQUILIBRIUM POINT, which is more commonly used, is defined in classic ways through various types of direct and indirect surveys.