Modelo sedimentario de la barrera medanosa a1 norte de Villa Gesell (provincia de Buenos Aires) - de aplicacion hidrogeológica

Abstract

Las localidades de Caril6 y Villa Gesell se han edificado sobre una barrera inedailosa de 110 inas de 1400 afios de antigiiedad. Con el fin de analizar la estratigrafia y sedimentologia del subsuelo de la zona, se recurrib a 15 perforaciones, realizadas en el predio del proyecto de Ciudad Marina de Port Dori, dondc pudieron identificarse tres estratos arenosos asignables a acuiferos, sobre la base de la description granulometrica de las muestras recolectadas, y conocidas coino Fm Punta Medanos, Fm Pozo NOR, j7 Fm Canal 5. Para confirmar la informacion, se realizaron ocho ensayos de bombeo. La infiltracion estA distribuida uniformemente sobre toda el area y el flujo del agua subterrinea es hacia el mar, con zonas intermedanosas donde aflora el nivel freatico. Durante 10s meses transcurridos entre 10s controles de la calidad de las aguas subterrineas, 10s parametros medidos (temperatura, pH, salinidad, oxigeno disuelto, turbidez) rcsultaron normales para 10s ambientes en que se practicaron las mediciones. Dada la baja densidad ocupacional de Carilb, 10s volfimenes aportados por precipitaciones en el irea son suficientes para abastecer la demanda durante lor dias de perano La transmisividad promedio obtenida es de 206.2 m2/dia para los acuiferos libres y de 130,97 m /dia para 10s semiconfinados. La permeabilidad promedio estiinada es de 18,23 m/dia y 4,19 m/dia, respectivamente.

Cariló and Villa Gesell localities were constructed on a barrier younger than 1,400 years BP. Dealing with the stratigraphic and textural characteritics of this area, 15 holes were drilled to a depth of 40 m at the property projected as “Ciudad Marina de Port Dora”. Three sandy strata were assigned to aquifers and test by pumping essays. These aquifers considered of hydrogeologic interest comprise the stratigraphical units called Punta Medanos, Pozo N°8 and Canal 5. The dune field is composed of transverse bodies oriented toward the north-northeast. Infiltration is uniformly distributed although at interdune ponds the water table is above the land surface. Water quality (temperature, pH, dissolved oxygen, turbidity) at the testing wells located close to the beach retrieves freshwater. In the sandy barrier from Villa Gesell and Cariló the sandy silts of hydrogeologic interest continue to depths below 40 m. The sedimentary record of the Eastern Barrier of Buenos Aires Province consists on a complex barrier (overlapping of barrier deposits of Quaternary age), modified during the Holocene transgressive-regressive cycle and where these transgressive and regressive processes are still being recorded at some locations (progradation of Punta Médanos, scarps of foredunes in Mar Chiquita). Considering the low density population of the area, precipitation is estimated as able to provide the volume of water needed during the summer season for the resort villages. Average trasmissivity is about 206 m2 /day for the free aquifer and 130 m2 /day for the semiconfined aquifers. Average permeability is 18.23 and 4.19 m/day at each type of aquifers.It is recommended to avoid the on-exploitation of the free aquifer in order to preserve their volumes, to prevent pumping cones and to avoid saline intrusions at the coast. The hydrogeologic reserves exceed the water volume supplied from the pampian silts (Buenos Aires formation) located to the west of the Route 11. The evaluation of these inputs of groundwater is recommended in order to better manage the semiconfined levels. Even though, recycling and reusing should be considered for the url~an grolvth planing. At the coastal barrier, belolv thc phreatic aquifer, a semiconfined horizontal lclrcl of variablc tliickness was recognised, and superinlposed to ;i scc:ond scilliconfined aquifer. 'This second serniconfinecl level with plane base and irregular top, is superimposccl to a thirct scmiconfinctl aquifer whose base was not drilled.