Ferramentas de gestão dos recursos hídricos: estudo de caso na bacia do baixo Rio Chambo (Equador)

Abstract

This work aimed to propose a territorial zoning based on the physiographic and morphological characteristics of the Lower Chambo River Basin (LCRB), located at the Province of Chimborazo (Ecuador), as a tool for the water resources management. The methodology used included the following activities: estimation of recharge from the local aquifers using the water balance and Darcinian estimates methods, conceptual model of groundwater circulation, groundwater and springs sampling for physico-chemical, chemical and isotopic analyses, as well as the estimates of supply and demand and the possible conflicts generated by the use and distribution of water. The results allowed to identify the occurrence of three multilayer aquifers of volcanosedimentary origin (Llío-Guano, Riobamba and Yaruquíes), composed of volcanic deposits from eruptions of Chimborazo, Igualata, El Altar and Tungurahua. The recharge of those aquifers comes, mainly, from the western (Chimborazo and Igualata) and eastern (El Altar and Tungurahua) mountain range and, secondarily, comes from the local precipitation. The discharge zone of surface water and groundwater comprises the Chambo River, considered as the confluence area of the drainages located in LCRB. The hydrochemical and isotopic data ( 18 O and  2 H) indicated the existence of waters with different compositions and origin. The Llío-Guano and Riobamba aquifers are composed of calcium-magnesium bicarbonate waters, from slightly acidic to neutral, with enriched  18 O and  2 H values. The Yaruquíes aquifer and the springs located in Cubijíes settlement are constituted, respectively, of sodium bicarbonate to calcium-magnesium sulfate waters with more depleted  18 O and  2 H values, indicating influence of the volcanic activities from El Altar. The area was divided into eight distinct zones (Z1, Z2, Z3, Z4, Z5, Z6, Z7, Z8), with particular morphological and water availability characteristics. The zoning will serve as a reference for the elaboration of water resource management plans in the Riobamba municipality and other Ecuadorian provinces.

Evaluation of nitrate concentrations in groundwater of Llío and San Pablo, Guano – EC

“…The work was carried out in the volcano-sedimentary basin of the river Chambo, in the inter-Andean depression, in this area the mesozoic basement is covered by sedimentary sequences, pleocene and pleistocene, constituted in the region by the Jurassic rocks of the Alao Paute Unit, Guamote, Daldal River, San Pablo de Sali and the Cretaceous rocks of the Peltetec Unit and Yunguilla Formation (Chidichimo et al, 2018;Mendoza, 2015;Procel, 2018). The units that form the base of the lower basin of the Chambo River, are located in the Cordillera Oriental, with respect to the study area that is the sector of Llío and San Pablo.…”

“…As described by Procel (2018) in the area there are three aquifers, of the multilayer type, called Llío-Guano, Riobamba and Yaruquíes. The Llío-Guano Aquifer is located near the Chimborazo and Igualata volcanoes, this aquifer is of the groundwater type (free), with double porosity, average width of 200 m, associated with the volcanogenic deposits of the Chimborazo (upper) and Cizarán (lower) formations.…”

“…To characterize the study areas, a cross-reference of bibliographic information was made, in addition to cartographic information, allowing us to know the areas of possible collection and also the flow of groundwater and the recharge zones of this (Chidichimo et al, 2018;Mendoza, 2015;Procel, 2018). Once this area was identified, the geological and stratigraphic description was made, determining the type of structure and rocks found in the subsoil of the aquifer, allowing to relate the composition of the rocks with the presence of nitrates in the water of Llío and San Pablo.…”

“…To define the anthropic areas and activities, the surrounding area was taken into account, indicating which are the direct and most intense anthropic activities that can influence the study area. These anthropic areas were determined by cartography, this information was used from several works carried out in the area of influence (Chidichimo et al, 2018;Mendoza, 2015;Mendoza et al, 2021;Procel, 2018).…”

“…Once the geological strata where the sampling points of the slope and the wells are located were identified, these were classified by the geological and stratigraphic composition. Afterwards, the results of water analysis of Llío and San Pablo were interpreted according to their geochemical composition, to determine the type of water and its origin, this through the diagram of Piper (Albo & Blarasin, 2014) and geological description made by Salguero (2017) and Procel (2018). The anthropic activities present in the area of influence were also identified and the nitrate concentration data were obtained temporarily.…”