Groundwater flow systems in mountainous terrain: 2. Controlling factors

The modeling technique developed in paper l (Forster and Smith, this issue) of this two‐part study provides a quantitative means for assessing the impact of factors controlling groundwater flow systems in mountainous terrain. Conditions to be examined include surface topography (slope profile, relief, three‐dimensional form), geology (permeability and thermal conductivity), climate (available infiltration, presence and extent of alpine glaciers, surface temperature conditions), and regional heat flux. Modeling results indicate that water table elevation is a sensitive indicator of the factors controlling mountain flow systems. Under certain conditions, overestimating the bulk permeability of a mountain massif by a factor of 5 can lead to underestimates of the water table elevation in excess of 1000 m. Under the same conditions, rates of fluid flux may be overestimated by at least 60%. The infiltration rate, regional heat flux, and the presence of glaciers have important, but lesser impacts. High topographic relief amplifies the influence of surface topography and permeable fracture zones on patterns of groundwater flow and on the position of groundwater flow divides. Although computed water table elevations are sensitive to controlling factors, uncertainties inherent in resolving the magnitude of many of the controlling parameters will complicate efforts to constrain simulations using measured water table elevations.