## 2 The Test Area  
For the present study, an area of 404 km\({}^{2}\) is taken as an experimental basis, which is located north of the capital of Colombia (Bogota D.C.) and includes the cities of Bucaramanga, Floridablanca, Piedecuesta and Tona (Figure 1). The study region is located in a sector called Massif Santandereano, which has a very rugged topography and is a geographical reference of vital importance, since it frames both geological and climatic conditions specific to the study region. Within the experimental area, a rugged topography is described, with an altitudinal elevation that ranges from 682 m to 3920 m. The difference between vertical topographic points is 3238 m and between horizontal points is 26.1 km; this indicates an altitudinal ascent of 124 m per kilometer, with a topographic mean of 2301 m. The region has a slope between 0\({}^{\circ}\) and 80\({}^{\circ}\), with an average of 26\({}^{\circ}\), and its greatest extension is between slopes of 23\({}^{\circ}\) to 32\({}^{\circ}\). Most of its surfaces are oriented to the west-northwest (247.5\({}^{\circ}\) to 337.5\({}^{\circ}\)). From a climatological point of view, the region has a varied climate, ranging from hot arid to cold humid, passing through humid temperate and humid high moorland (Instituto de Hidrologia, Meteorologia y Estudios Ambientales-IDEAM [36]). Precipitation values ranging from 66 to 140 mm with temperatures between 23 \({}^{\circ}\)C and 29 \({}^{\circ}\)C above the topographic level of 950 m (city of Bucaramanga), and precipitation values between 14 and 100 mm with temperatures between 8 \({}^{\circ}\)C and 14 \({}^{\circ}\)C above the topographic level of 1950 m (northeastern region) are estimated [36].  
In terms of geology, the region is made up of sedimentary, igneous and metamorphic rocks, dating from between the Precambrian supereon and the Quaternary period, where 55% correspond to metamorphic rocks (schists, phyllites, gneiss, mgmatiites and quartzites) from the period between Precambrian and Pre-Devonian; 31% are igneous rocks (quartz-monzonitic and granites), most commonly from the Triassic-Jurassic period, and 14% are sedimentary rocks (sandstones, limestones, conglomerates and shale), most commonly from the Cretaceous period, in addition to deposits from the Quaternary period [37]. Tectonically, the study region falls within the structure of the Santander Massif that is located within the eastern mountain range of Colombia and presents conditions of crustal deformation due to uplift processes, with transpressive and transcurrent events, and compressive deformation with folding in sedimentary rocks, which generates different degrees of deformation [38; 39].  
Structurally, the main feature of the study region is framed by the stroke of the Bucaramanga Fault, which is a regional structure with a combined component in the strike (sinestral) and in the dip (reverse), with an NNW-SSE direction [37; 39; 40]. From the geomorphological point of view, the region is characterized by a development of very large areas where there is the interaction of processes such as sedimentation in the lower partsand active erosion in the mountainous region, with an abrupt relief, straight and steep slopes, rounded and sharp blades and deep and rectilinear drainage. It demonstrates a subparallel drainage pattern, parallel to subdendritic, with \"V\" shaped valleys typical of a relief with strong structural control [38].