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HYDROLOGICAL ANALYSIS OF THE COMBEIMA RIVER BASIN

MORPHOMETRY The physical characteristics of a basin have a close relationship with the behavior of the flows that pass through it, however, there is difficulty due to the little cartographic information available, which makes finding that relationship not easy and limited. On the other hand, it cannot be guaranteed that all the morphometric information used for the study can be obtained on the same scale, increasing the uncertainty about the reliability of the parameters.

MORPHOMETRIC ANALYSIS OF THE COMBEIMA RIVER BASIN The Combeima river is born in the Nevado del Tolima, on the eastern flank of the central mountain range and ends at the Coello river, after having traveled a distance of approximately 53.5 km; This channel plays a determining role in the department, since it supplies water to numerous urban, rural and industrial areas. The Combeima river basin is made up of 21 micro-basins, constituting an area of 27,364 ha, a perimeter of 117.30 km, a maximum width of 11.6 km, and a maximum length of approximately 57.78 km. In order to carry out the morphometric analysis of the basin, the following indices were taken into account: Compactness Kc = 2, elongation LI don't knowa = 2.36I don't know, asymmetric II don't knowas = 1 I don't know , 13, and form factor F = 0.077. Taking these results as a reference, it was possible to determine that the Combeima river basin has an oblong oval or oblong rectangular shape, with a significant elongation, therefore, the main river of the basin is long. The distribution of the basin in relation to the main channel tends to be homogeneous, that is, asymmetric. On the other hand, the average slope of the basin was determined, which is 44.1%, indicating that the relief in which the basin is located is very strongly rugged. The average elevation of the basin corresponds to 2,535.98 m., Which indicates that in this contour line the area of the basin is divided into two equal parts; This parameter allows knowing the temperature and the effect on the loss of precipitation by evaporation. Taking into account the massive coefficients of 9.26 and the orographic coefficient of 0.0238, we determined that the basin is moderately mountainous, with a low rugged terrain and a low potential for degradation.

From the application of the hierarchy proposed by HORTON AND SCHUMM (1945), where it is defined that “Every channel without tributaries is of order 1, at the confluence of two channels of order U a segment of channel of order u originates +1 ”, it was identified that the Combeima river basin is of the fourth order. Regarding the relationship between the total length of the channels that make up the basin and its area, the density of the drainage network was established (DI don't knowd)I don't know which is 1.18 km / km2, that is to say that there are 1.18 channels per km2I don't knowwithin the basin, being part of the moderate category; on the other hand, it can be established that the basin is poorly drained, and therefore little runoff is generated. The type of drainage is dendritic and according to its shape it is classified as irregular winding. The Torrentiality coefficient (Ct), which measures the degree of torrentiality of the basin, in the case of the Combeima river basin is 0.57 km2 I don't know, which indicates that the basin has few water currents and its intensity is minimal, indicating a low erosive potential. The analysis of the slope of the main channel is important, since it identifies the capacity of the waters within the basin to transport sediments; When applying the Taylor and Extreme Elevations methods, the slope of the channel is between 2.97% and 7.08%, which indicates that the river velocities are not very high, therefore, the erosive potential and sediment drag they are very low. Taking into account the slope, the time it takes for a drop of water to arrive, from a distant point to another point of interest within the basin, is determined to be an average of 4.12 hours, for which Kirpich's methods were taken into account, Californian Kirpich and the formula of the Bureau of Reclamation, and the Guaire Formula was not taken into account, since its value is 2.7 hours, and it generates a bias within the average. Finally, it is recommended to constantly monitor the Combeima river, since it is an important source for water supply both in the municipality of Ibagué, as well as in numerous sidewalks and industries located within the basin; It should be noted that this is a river susceptible to contamination due to the characteristics set out above. The Combeima river basin presents innumerable environmental services at the local and regional level, being a strategic ecosystem by providing 80% of the water for the aqueduct of the city of Ibagué and for generating an important water supply for the development of the different productive activities of the region.

As previously mentioned, the surface water resources of the Combeima river basin are used in a greater proportion to supply 80% of the water for the municipal aqueduct of Ibagué, which the basin has 98,434 registered users until 2008, with this purpose 1,600 L / sec are taken, and 250 L / sec are taken from its tributary La Quebrada Cay. On the other hand, water is also demanded for the production of electrical and motor energy, and for the irrigation of 7000 Ha of highly technical crops such as rice and sorghum, located mainly on the Ibagué plateau, which make up a total demand of 214 million of mI don't know3I don't know/ year, which shows a high pressure on the water resource. It is important to highlight that the different anthropic actions accelerate and increase the effects of the phenomena of avalanches, landslides, floods, gales, strong winds, overflows, mainly due to the destruction and loss of the protective vegetation cover, burning and clearing of forests, overgrazing and inappropriate production techniques. The scarcity index relates the percentage of the water demanded by the set of economic and social activities with the available water supply, in the case of the Combeima basin this index is equivalent to 0.36, evidencing a high level of vulnerability compared to the from other basins. Thanks to an analysis carried out by a group of master's students and the document being published in the virtual library of the Ministry of the Environment, it was possible to determine that the yields were found according to a water sectorization, the first sectorization covers from birth from the river to the town of Juntas, with a drained area of 88,516km2; the second corresponds to a drained area of 106,965Km2, and the fourth sectorization from the source of the river to the Yuldaima station which drains an area of 226 Km 2. According to the calculated water yields for these four stations, 32.7 it-second-Km2 in jousting, 36.5 in San Vicente, 44.5 in Montezuma and 41.0 in Yuldaima, an increase in water wealth can be seen as you descend from Juntas, to get your maximum at the Motezuma station. This allows us to conclude that the richest part from the hydrological point of view is between the middle part between Juntas and Ibagué. The daily flow duration curve allows us to conclude that the Combeima River can contribute, in addition to what is being collected, about 3,000 its-sec with 80% security, or about 2,500 its-secwith a security of 90% and finally about 2000 its-sec with a security of 95%.

This water supply is being affected by the deforestation processes of the slopes, the inappropriate location of human settlements, the inappropriate use of the paramo area (potrerización), resulting in irregularity in the river regime, water contamination, and loss in flow regulation. The waters of the Combeima river from the Pastales farmhouse concentrate a medium degree of contamination (65-80% oxygen saturation), which becomes high on the route between Chapetón and the Martyrs (30-65% saturation of Oxygen), on its way through the city of Ibagué. The best water quality occurs in the Parque de los Nevados Transect up to the town of Juntas with values above 90% oxygen saturation. Currently, with the aim of recovering the water regime and the stability of the soils, the implementation of activities that contribute to the recovery of the channels of the Combeima river and the Cay gorge has been prioritized; Promotion activities include erosion control works, multi-purpose reforestation programs, cleaner production projects. Likewise, it seeks to maximize access to drinking water and basic sanitation services, where the aim is to recover the infrastructure of the intakes of Combeima and Cay, since they have been repeatedly affected by floods and destruction.

MAP OF THE COMBEIMA BASIN...