REGIONAL FLOW FREQUENCY ANALYSIS OF RIVER BASIN WITH HEADWATERS AT THE ANDES CORDILLERA
Alberto Ismael Juan Vich, Federico Augusto Norte, Carolina Lauro
Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA-CONICET), Av. Adrian Ruiz Leal s/n, Parque General San Martín, 5500 Mendoza, Argentina
Instituto de Estudios del Ambiente y Recursos Naturales, Facultad de Filosofa y Letras, Universidad Nacional de Cuyo, Centro Universitario, Parque General San Martn, 5500 Mendoza, Argentina.
Manuscript received on 10 December 2012, in final form on 16 August 2013
ABSTRACT
The aim is to determine the magnitude of flow variables for return periods much longer than the observed and to obtain the correspondent quantil for sites with scarce data using a Regional Frequency Analysis approach based on L – moment statistics (ARF-LM). The area under analysis comprises mountain basins between the Bermejo and the Santa Cruz rivers.
Thirty-two gauging stations were analyzed and five variables were determined: annual ow (Qaño) and seasonal flows: winter QI (july, august, september), spring QP (october, november, december), summer QV (january, february, march) and autumn QO (april, may, june), from the average daily flow observed. Independence, randomness, normalcy, and homogeneity conditions were verified. Normalcy is rejected in 60% of the cases, summer and autumn flows being the variables with the least degree of normalcy. Lack of both independence and randomness occurs in 34% of the series analyzed, notably the winter and autumn flows with a level of significance of 5 %.
The Los Patos, San Juan, Cuevas, Diamante, Atuel, Grande, Valenzuela, Poti Malal, Neuquén and Santa Cruz rivers did not show any significant trends in the variables analyzed.
A statistically significant increasing trend was detected in some variables and locations of northwestern and central-western of Argentina while a decreasing trend was observed in some variables and locations in the Patagonian Andes. Flows Qaño), QI and QV show abrupt changes in over 65% of the cases while QP only in 44 %. In general, the jump in mean values took place in the 1970s.
A homogeneous region was identified for each of the five variables. Homogeneity was verified by means of discordance and heterogeneity tests and the best-fit distribution through ZDIST and PUMT measures. The distributions used were: generalized extreme values, generalized logistic, generalized normal, normal, Gumbel, generalized Pareto, exponential, and Pearson III. In all cases the homogeneous region includes only stations in the southern Central Andes, from the Tunuyan to the Colorado river. The Pearson III and Gumbel distributions exhibit the best fit.