Estimating groundwater inflow and leakage outflow for an intermontane lake with a structurally complex geology: Georgetown Lake in Montana, USA

Shaw, Glenn D.; Mitchell, Katie L.; Gammons, Christopher H.

Estimating groundwater inflow and leakage outflow for an intermontane lake with a structurally complex geology: Georgetown Lake in Montana, USA | Estimation des flux d’eaux souterraines d’entrée et de sortie par fuite d’un lac de montagne en contexte géologique structural complexe : lac de Georgetown dans le Montana (Etats-Unis d’Amérique) Estimación de la afluencia y efluencia por filtración del agua subterránea en un lago intermontano con una geología estructuralmente compleja: Lago Georgetown en Montana, EEUU 利用结构上复杂的地质条件估算山间湖泊地下水流入量及渗漏流出量:美国蒙塔纳州乔治城湖 Estimando a afluência das águas subterrâneas e saída por escoamento para um lago entre montanhas com uma geologia estruturalmente complexa: Lago Georgetown em Montana, EUA

2017

Shaw, Glenn D. | Mitchell, Katie L. | Gammons, Christopher H.

Stable isotopes of the water molecule (δ¹⁸O and δD) for groundwater, lake water, streams, and precipitation were coupled with physical flux measurements to investigate groundwater–lake interactions and to establish a water balance for a structurally complex lake. Georgetown Lake, a shallow high-latitude high-elevation lake, is located in southwestern Montana, USA. The lake is situated between two mountain ranges with highlands primarily to the east and south of the lake and a lower valley to the west. An annual water balance and (δ¹⁸O and δD) isotope balance were used to quantify annual groundwater inflows of 2.5 × 10⁷ m³/year and lake leakage outflows of 1.6 × 10⁷ m³/year. Roughly, 57% of total inflow to the lake is from groundwater, and 37% of total outflow at Georgetown Lake is groundwater. Stable isotopes of groundwater and springs around the lake and surrounding region show that the east side of the lake contains meteoric water recharged annually from higher mountain sources, and groundwater discharge to the lake occurs through this region. However, springs located in the lower western valley and some of the surrounding domestic wells west of the lake show isotopic enrichment indicative of strong to moderate evaporation similar to Georgetown Lake water. This indicates that some outflowing lake water recharges groundwater through the underlying west-dipping bedrock in the region.

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