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La cuenca superior del arroyo Napostá Grande se ubica en el SO de la provincia de Buenos Aires. Para la subcuenca superior, se dispone de registros de caudal y precipitaciones (P) durante 1936-1945. El objetivo de este estudio se orienta hacia la elaboración de la curva de evapotranspiración real (ETR) normal para la subcuenca mediante el método de balance hídrico, para predecir la respuesta hídrica en ciclos de larga duración. Para esto, de acuerdo a las características de la subcuenca, se estableció un valor de intercepción del 10% de P. Los resultados mostraron una marcada correlación entre P y ETR y que, en general, una parte significativa de P es convertida en ETR. Además, se observó que para los registros disponibles de precipitaciones acumuladas mensuales más altos, la parte de P que es transformada en ETR muestra una dispersión más alta y una tendencia general a disminuir. Este comportamiento es atribuido parcialmente a la rápida evacuación de precipitaciones extraordinarias causadas por las altas velocidades de crecidas que caracteriza esta subcuenca serrana. En cuanto a la ETR normal mensual, se encontró que la variación del parámetro durante el año sigue el régimen de precipitaciones de la subcuenca, con valores más altos en primavera y verano. Los valores medios de ETR normal resultaron similares a las magnitudes reportadas en estudios previos por otros autores en la misma subcuenca, donde se aplicaron otras metodologías. La gráfica de ETR normal resulta aceptable en periodos de 10 años o más de registros en la subcuenca de estudio, recomendándose para la comparación de distintos ciclos hídrico-hidrológicos. Reestablecer los registros hídricos contribuiría a detectar alteraciones significativas del balance hídrico, en particular a la ETR de la subcuenca, pudiendo abordar acciones destinadas a la preservación del recurso. Abstract The Napostá Grande stream basin is located in the SW of the Buenos Aires province. For the upper sub-basin, flow and rainfall (P) records corresponding to the period 1936 – 1945 are available. The objective of this study is oriented towards the construction of the normal real evapotranspiration (ETR) curve for the upper sub-basin through the method of hydric balance, in order to predict the hydric response for cycles of long duration. For this purpose, the daily records were reorganized into monthly accumulated registers and, according to the sub-basin’s characteristics, an interception value of 10% of P was established. The results revealed that a marked correlation between P and ETR exists and, in general, a significant part of P is converted into ETR. Moreover, it was observed that for the highest registers of accumulated monthly rainfall available, the part of P that is transformed into ETR shows a higher dispersion and a general tendency to decrease. This behavior is attributed partially to the rapid evacuation of extraordinary rainfalls caused by the high overflow speed that characterizes this hill-mountain sub-basin. Regarding the normal monthly ETR, the variation of this parameter during the year is found to follow the precipitations regime, with higher values in the spring and summer. The average values of normal ETR turned out to be similar to the magnitudes reported in previous studies by other authors in the sub-basin, where different methodologies were applied. The normal ETR graphic turns out acceptable in periods of 10 years or more of records in the studied sub-basin, being recommended for the comparison of different hydric-hydrological cycles. Re-establishing the hydric records would contribute to detect significant alterations in the hydric balance, in particular the ETR of the sub-basin, and would allow to take actions aimed at preserving the natural resource.

The total suspended solids (TSS) concentration is a relevant parameter for stream management. A high content of TSS has a negative impact on the ecological habitats and the aquatic environment, and could also be a limitation for the exploitation of surface water. The determination of TSS concentration through water sampling and posterior laboratory analysis is a complex and economically expensive procedure. In this regard, turbidity arises as a useful surrogate measure that allows the indirect estimation of the TSS concentration in a simple and economically convenient way. In the context of a severely deteriorated water supply system, the Naposta Grande stream constitutes a valuable resource for human and industrial consumption in the City of Bahia Blanca. The general objective of the present investigation is to develop statistically based relations between the parameters involved in the suspended solids transport, in order to characterize this phenomenon through the measurement of variables of simple and straightforward field determination. The statistical relationship between the TSS concentration and turbidity and between discharge and solid flow rate was explored. In both regression analyses, the statistical correlation resulted highly significant, and therefore represent valid calibration tools for future solids transport modelling analysis and prediction as well as for sedimentological balances. A comparative analysis of the solids transport between the closure of the medium drainage basin and at the outer limit of the suburban area of Bahia Blanca City, suggests the existence of erosive processes affecting the stream bed and its margins at the section between both sites.

El crecimiento de la comarca serrana a la vera del río Sauce Grande representa un desafío frente al abastecimiento poblacional de agua y el desarrollo económico. Los objetivos fueron evaluar algunas características del agua superficial para consumo humano y cría de peces en tres sitios del cauce principal y describir la variación estacional entre ellos. Se registraron, entre febrero y diciembre de 2015, temperatura del agua, pH, oxígeno disuelto (OD), turbiedad y sólidos disueltos totales (TDS) en E1, E2, E3 (nombrados hacia la naciente), y lecturas limnigráficas en E1 y E2, determinándose caudales. La temperatura del agua varió entre 6,7 y 22,5 ºC, resultando similar en los sitios muestreados, excepto en primavera de 2015 donde se registraron valores inferiores en E1. El pH se halló entre 6,2 y 7,2 y resultó E1> E2 y E3 en primavera y verano. El OD se halló entre 8,7 y 13,5 mg/L, aumentando en los tres sitios desde el período estival al invernal, y a la inversa. Los valores de TDS y turbiedad se hallaron en rangos de 113-346 mg/L y para NTU de 4,2-52,3. Para ambos resultó E1> E2 y E3, excepto turbiedad en febrero de 2015. Se obsevaron en E1 y E3, crecidas en febrero de 2015, con aumento pronunciado de turbiedad y marcada disminución de TDS y OD en E3, y agosto de 2015, donde no se observaron variaciones significativas de turbiedad y TDS. En septiembre de 2015 se observó en E1 aumento de turbiedad, disminución de TDS y mínimo pH en coincidencia con una crecida. No hubo diferencias significativas entre E2 (hoya) y E3 (vado). Los parámetros fisicoquímicos muestreados resultaron adecuados para la supervivencia de la vida acuática. Se requieren estudios costo-eficiencia para tratamiento de la turbiedad para consumo humano. Se recomienda continuar monitoreando E1 y E3 e incorporar nuevos sitios y parámetros de muestreo. Abstract The mountainous tourist region growth at Sauce Grande riverside represents a challenge to human water supply and the economic development. The aims of this study were to evaluate some characteristics of surface water for human consumption and fish farming at three sites in the main course, and to describe the seasonal variation between them. From February to December 2015 were recorded water temperature, pH, dissolved oxygen (DO), turbidity and total dissolved solids (TDS) at E1, E2 and E3 (towards the source of the river). In E1 and E2 were made limnigraphic readings and flow measurement. Water temperature ranged between 6,7 and 22,5 ºC, resulting similar at studied sites, except in spring 2015 where lower values were recorded at E1. Levels of pH were between 6,2 and 7,2 and were higher at E1 with respect to E2 and E3 in spring and summer. DO concentration was between 8,7-13,5 mg/L, increasing its values in all three sites from summer to winter period, and backward. TDS and turbidity values were found between 113-346 mg/L and 4,2-52,3 for NTU. For both parameters resulted E1> E2 and E3, except turbidity in February 2015. There were observed floods at E1 and E3 in February 2015 with pronounced increasing of turbidity and significant decrease in TDS and DO at E3, and in August 2015, when no significant variations of turbidity or TDS were observed. Increase in turbidity, decrease in TDS and minimum pH at E1 was observed in September 2015 matching with a flood. There were no significant variations between E2 (pond) and E3 (ford). The observed physicochemical parameters resulted suitable for aquatic life survival. Cost-efficiency studies are necessary for treatment of turbidity of water for human consumption. It is recommended to continue monitoring E1 and E3 and incorporate new stations and sampling parameters.