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Management of dewatering schemes in an open cast mine operation using groundwater fow modeling: a case study of karst aquifer, Tamil Nadu, India

Mohan Sankaralingam, Pramada Subhashini Kumudesan, Anju Maramvittil

Acta Geophysica

2022

Vol. 70, no 1

283--303

An efficient dewatering scheme helps the management authority of mines in decision-making on the minimum quantity of withdrawal of groundwater from open-cast mines to avoid excessive groundwater withdrawal from the mines. Karst aquifers are characterized by a dual flow system consisting of Darcy flow and non-Darcy flow in the Matrix and conduits respectively. Due to lack of site-specific data, it is difficult to model the flow behavior in the dual flow system. This study evaluated equivalent porous medium (EPM) approach and the hybrid approach/combined discrete-continuum approach (CDC) for modeling groundwater flow in a karst aquifer and found that hybrid approach is suitable for modeling the flow in the karst aquifer system. Hybrid approach is applied to derive the optimum dewatering scheme for safe mining of limestone in the Adanakurichi limestone mines of Tamil Nadu, India and was found that an additional 20% increase in pumping is required in the year 2020 compared to 2016 to bring the water level to the limestone bottom. Wavelet coherence diagram was used to identify the interrelation between rainfall and groundwater levels, and also between the groundwater levels at different locations. The results from the study will be helpful for the better management of groundwater control operations in karst aquifers, under various safe level of operations. MODFLOW 2005 was used to model the aquifer based on EPM approach and for modeling based on hybrid approach conduit fow process (CFP) Mode 1in MODFLOW was used.

Assessment of Ras El Ma Karst Spring Features by Structural and Functional Approaches at the Region of Taza, Morocco

Naoura Jamal, El Kati Imad, Benaabidate Lahcen

Journal of Ecological Engineering

2021

Vol. 22, nr 9

32--47

This work performed by considering two complementary approaches for investigating the Karst system of Ras El Ma source: (1) The structural approach based on field studies, (2) The functional approach requiring inputs data (precipitations) as well as output data at the exit of the karstic system. The choice of the Ras El Ma source is justified by the fact that it constitutes the main outlet of the Liassic aquifer at the Southwest of Taza town. The structural approach highlighted that the impact of South Rifan and North Middle Atlas faults, oriented mainly NE-SW to ENE-WSW and NW-SE, tectonically linked to the Hercynian and late-Hercynian phases; these faults compartmentalized the karst into panels. The functioning of this karst system is based on the coupling of inputs and outputs, the analysis of interannual hydrograph, flood hydrographs, the recession curves and the analysis of hydrogeochemical results. Respectively, the obtained results are presented as follows: A close relationship between flow rates and precipitation, interannual hydrographs marked by a contrasting variation in flow rates and a periodicity that occurs between low water and high-water years. Concerning flood hydrographs, there are two types, a unit modal hydrographs type which generally occurs following time concentrated rainfall and a second multi modal hydrographs type which follows the repetitive rainfall in the basin. The study of recession curves reveals a clear complexity of the systems supplying the source. However, due to the low drying-off coefficients (7.66∙10-4), the aquifer seems to have a poorly developed drainage network in a flooded area. According to the Mangin method [1975], this karstic system is classified in the category of poor or complex karst systems taking into accounts two parameters (i) and (K), which characterize the functioning of the infiltration zone and the volume of flooded karst, respectively. The physicochemical parameters study highlighted the nature of drained rock by the sources. The correlation between conductivity and different chemical elements shows that bicarbonates and calcium are responsible for the mineralization of the waters of this source. It can be concluded that the low values of mineralization occur during the winter and spring floods. The spring regains its normal mineralization during the summer period.