Caracterización morfométrica de la cuenca alta del río Salí mediante el uso de sistemas de información geográfica

MARÍA SOLEDAD BUSTOS; SERGIO M. GEORGIEFF

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentino; 2017

Asociación Geológica Argentina

Morphometric characterization of the upper Salí river basin through the use of Geographic Information Systems. A watershed receives water that precipitates as rain and conducts it into drainage networks. The response to the rain depends on its morphometric characteristics related to geology, topography and climate, among other factors. Tapia - Trancas basin is a tectonic depression located to the north of Tucumán province; it formed during Andean orogenesis (Abascal 2005). Its boundaries are the Sierras Pampeanas to the west, the Sierras Subandinas to the east, the Celestino Gelsi dam, to the south and Campo del Tala, in Salta province, to the north. This basin constitutes the drainage area of the upper Salí river and is the main source of water for the supply of Celestino Gelsi dam, which generates electric power, water for irrigation and drinking water for San Miguel de Tucumán and surroundings. One of the main problems of the basin is the gradual loss of the capacity dam, due to the filling with sediment (Adler 2004). The objective of this research was to identify the natural factors that control sediment and water discharge inthe Salí river and its tributaries, and to identify the areas that require specific management actions. For this purpose, the Horton - Strahler analysis was performed using the SRTM digital elevation model (Farr et al. 2007). The DEMwas processed according to Fleming and Dohan (2009), in a geographic information system. Raster layers representing flow direction and flow accumulation were obtained. The drainage network was automatically defined setting a threshold of 0.3% of the area. This produced vector layers representing the sub-basins divide and the drainage network. Data obtained were used to derive the following morphometric parameters: area, length, order number, bifurcation ratio (Rb) and length ratio (Rl), drainage density (Dd), river frequency (Fr), storage coefficient (RHO), torrentiality coefficient (Ct), mean runoff extension (E), and longitudinal profile graphs. According to the results the basin area covers 5312km2 of which the Tala river subbasin accounts for 33.6%. El Tala river had also the longest drainage network (400 km). Mean Rb varied between 2 (Tapia river) and 3.6 (Candelaria river), this values would indicate a moderate structural control over the fluvial pattern. The Rl had its lowest value at Tala river (0.7) and the highest at Choromoro river (5,6). The relationship between order number, mean length and number of rivers showed a geometric tendency according to drainage networks composition laws (Knighton 1998). The highest RHOvalue characterized the Choromoro river (1.8) indicating that it takes more time to reach the maximum discharge and that erosive processes are attenuated in this subbasin, the opposite characterized Candelaria and Tala rivers (lowervalues). According to the Ct, the rivers with the lower erosive susceptibility are Choromoro (0.009) and Vipos (0.015), while India Muerta (0.024), Tala (0.022) and Candelaria (0.021) had greater susceptibility. The mean runoffextension indicated that a longer time is needed to reach the peak flows in the Choromoro (maximum E = 2.1) and Tapia basins, while shorter time characterized India Muerta (minimum E = 0.001), followed by Acequiones, Candelaria and Tala. The Dd was greater for the Acequiones and Candelaria rivers. According to Horton (1945), under similar climate conditions, the hydrological networks developed on impermeable rocks have a higher drainage density than those developed in permeable rocks. The Fr was higher at the Tapia and Tala rivers, which indicated a greater availability of surface water, less soil permeability and greater susceptibility to erosion, the opposite situation characterized to India Muerta stream (Fr = 0.001). Generally, longitudinal profiles had concave shapes Tapia, Candelaria and India Muerta stream had steeper and more uniform slopes along the whole channel. Knickpoints were observed in the profiles of Tala, Choromoro and Vipos rivers. The Candelaria and Tala rivers stand out due to the occurrence of shorter times to reach the maximum flow rate and greater erosive susceptibility. An opposite situation was observed for the Choromoro river. Further research is required in these areas to focus control measures.