Ground Water Flow Modeling with Sensitivity Analyses to Guide Field Data Collection in a Mountain Watershed

Abstract

In mountain watersheds, the increased demand for clean water resources has led to an increased need for an understanding of ground water flow in alpine settings. In Prospect Gulch, located in southwestern Colorado, understanding the ground water flow system is an important first step in addressing metal loads from acid‐mine drainage and acid‐rock drainage in an area with historical mining. Ground water flow modeling with sensitivity analyses are presented as a general tool to guide future field data collection, which is applicable to any ground water study, including mountain watersheds. For a series of conceptual models, the observation and sensitivity capabilities of MODFLOW‐2000 are used to determine composite scaled sensitivities, dimensionless scaled sensitivities, and 1% scaled sensitivity maps of hydraulic head. These sensitivities determine the most important input parameter(s) along with the location of observation data that are most useful for future model calibration. The results are generally independent of the conceptual model and indicate recharge in a high‐elevation recharge zone as the most important parameter, followed by the hydraulic conductivities in all layers and recharge in the next lower‐elevation zone. The most important observation data in determining these parameters are hydraulic heads at high elevations, with a depth of less than 100 m being adequate. Evaluation of a possible geologic structure with a different hydraulic conductivity than the surrounding bedrock indicates that ground water discharge to individual stream reaches has the potential to identify some of these structures. Results of these sensitivity analyses can be used to prioritize data collection in an effort to reduce time and money spend by collecting the most relevant model calibration data.

Analysis of groundwater flow in mountainous, headwater catchments with permafrost

“…First, the groundwater flow system is more sensitive to hydraulic conductivity than the percent of precipitation infiltrating as recharge. This agrees with prior work that groundwater responses are most sensitive to hydraulic conductivity [e.g., Johnson , ; Voeckler et al ., ]. Second, since decreasing the recharge percent produces results similar to hydraulic head and baseflow values, recharge percents utilized in the base case are likely an upper bound for this simulation.…”

Electrical Resistivity Characterization of a Reclaimed Gold Mine to Delineate Acid Rock Drainage Pathways

“…Whether natural or anthropogenically caused, ARD poses problems for local watersheds, including streams (Bird 2003;Parker et al 2007), soil (Da Silva et al 2005;Finlayson et al 2000;El Khalil et al 2008;Liu et al 2003), ground water (Brown et al 1998;Johnson 2007;Malmstrom et al 2008), and aquatic life (Fischer and Sexauer 2002;Mian and Yanful 2003;Passariello et al 2002;Saiki et al 2001;Salomons 1995).…”

Modelling of hydrogeochemical potential of three lake catchments in Polesie region (Eastern Poland)

“…There are various modelling approaches to estimate water quality (Kopmann and Markofsky, ; Johnson, ; Refsgaard et al ., , etc.). The most popular are Agricultural Nonpoint Source Pollution Model, Areal Nonpoint Source Watershed Environment Response Simulation or The Soil Water and Assessment Tool (FitzHugh and Mackay, ; Abbaspour et al ., ).…”