Patricia Claudia Laurencena

Recharge assessment in an urban area: a case study of La Plata, Argentina

Leakage from water mains, storm drainage and sewer systems in urban areas constitutes a source of recharge that is difficult to identify and quantify at a regional scale. The objective of this work is to apply a methodology that would make it possible to evaluate urban recharge at a regional scale, taking as a case study the city of La Plata (Argentina). In the study area, population growth and an increase in water demand has caused the intensive exploitation of groundwater with resulting alteration in groundwater flow. The methodology used was developed on the basis of a water balance and the simulation of the temporal evolution of the cones of depression and the volumes of water extracted from the aquifer. The method consists of adjusting the piezometry resulting from the numerical modelling to the measured piezometry, by means of the variation of the recharge parameter in the urban area. The results obtained make it possible to identify and quantify urban recharge, which in this case represents a volume of water similar to the recharge from precipitation.RésuméFuite de conduites maîtresses, drainage des orages et systèmes d’égouts en zones urbaines constituent des sources de recharge qu’il est difficile d’identifier et de quantifier à une échelle régionale. L’objectif de ce travail est d’appliquer une méthodologie qui rendrait possible l’évaluation d’une recharge urbaine à une échelle régionale, prenant comme cas la ville de La Plata (Argentine). Dans la zone d’étude, la croissance de la population et l’augmentation de la demande en eau ont causé une exploitation intensive de la nappe avec altération résultante du débit d’écoulement souterrain. La méthodologie utilisée a été développée sur la base d’un bilan d’eau et de la simulation de l’évolution temporelle des cônes de dépression et des volumes d’eau extraits de l’aquifère. La méthode consiste à ajuster la piézométrie résultant de la modélisation numérique à la piézométrie mesurée, au moyen de la variation des paramètres de la recharge dans la zone urbaine. Les résultats obtenus ont rendu possible l’identification et la quantification de la recharge urbaine, qui dans ce cas représente un volume d’eau similaire à la recharge des précipitations.ResumenLas pérdidas de las cañerías de aprovisionamiento de agua, de los drenajes pluviales y cloacas, constituyen una recarga urbana que es de difícil identificacion y cuantificación a escala regional. El objetivo del trabajo es aplicar una metodología que permita evaluar la recarga urbana a escala regional tomando como caso de estudio a la ciudad de La Plata (Argentina). El crecimiento poblacional y el aumento en la demanda de agua produjeron una explotación intensa de las aguas subterráneas con la consecuente alteración del flujo subterráneo. La metodología usada se desarrolló partir de un balance de agua y la simulación de la evolución temporal de los conos de depresión y los volúmenes de agua extraídos del acuífero. El método consiste en ajustar la piezometría resultante del modelo numérico a la piezometría medida, mediante la variación del parámetro de recarga en el área urbana. Los resultados obtenidos permiten identificar y cuantificar la recarga urbana la cual representa, para este caso, un volumen de agua similar a la recarga proveniente de las precipitaciones.ResumoAs fugas a partir de canalizações de águas de abastecimento, de águas pluviais e de águas residuais em áreas urbanas constituem uma origem de recarga que é difícil de identificar e quantificar a uma escala regional. O objetivo deste trabalho é a aplicação de uma metodologia que tornasse possível avaliar a recarga urbana a uma escala regional tomando como estudo de caso a cidade de La Plata (Argentina). Na área de estudo, o crescimento populacional e um incremento na procura de água causaram uma exploração intensiva da água subterrânea com a consequente modificação no escoamento da água subterrânea. A metodologia usada foi desenvolvida com base no balanco hídrico e na simulação da evolução temporal dos cones de rebaixamento com os volumes de água extraídos do aquífero. O método consiste no ajuste da piezométrica resultante da modelação numérica com a piezométrica medida, através da variação do parâmetro de recarga na área urbana. Os resultados obtidos tornam possível identificar e quantificar a recarga urbana, que neste caso representa um volume de água similar ao da recarga proveniente da precipitação.

Ionic exchange in groundwater hydrochemical evolution. Study case: the drainage basin of El Pescado creek (Buenos Aires province, Argentina)

The phreatic aquifer beneath the Pampean plain, in eastern central Argentina, constitutes a relevant source of water supply in the area. The objective of this work was to assess the significance of the cation exchange processes in the hydrochemical evolution of this aquifer, based on a study case located in the middle and upper basin of the El Pescado creek. Results indicate that Ca2+/Na+ exchange is the main process determining the evolution of groundwater from the recharge areas (Ca–HCO3) towards the local discharge areas (Na–HCO3), as well as representing a source of Na+ contribution to the water in the aquifer. This hydrochemical characteristic is central to the identification of local discharge areas within a plain environment which extends regionally. The ion exchange capacity of these discharge areas has environmental importance, due to its influence on groundwater quality and potential groundwater uses. These results may be applied to any aquifer sharing similar hydrogeological characteristics.