title: Using high hydraulic conductivity nodes to simulate seepage lakes.
abstract: In a typical ground water flow model, lakes are represented by specified head nodes requiring that lake levels be known a priori. To remove this limitation, previous researchers assigned high hydraulic conductivity (K) values to nodes that represent a lake, under the assumption that the simulated head at the nodes in the high-K zone accurately reflects lake level. The solution should also produce a constant water level across the lake. We developed a model of a simple hypothetical ground water/lake system to test whether solutions using high-K lake nodes are sensitive to the value of K selected to represent the lake. Results show that the larger the contrast between the K of the aquifer and the K of the lake nodes, the smaller the error tolerance required for the solution to converge. For our test problem, a contrast of three orders of magnitude produced a head difference across the lake of 0.005 m under a regional gradient of the order of 10(-3) m/m, while a contrast of four orders of magnitude produced a head difference of 0.001 m. The high-K method was then used to simulate lake levels in Pretty Lake, Wisconsin. Results for both the hypothetical system and the application to Pretty Lake compared favorably with results using a lake package developed for MODFLOW (Merritt and Konikow 2000). While our results demonstrate that the high-K method accurately simulates lake levels, this method has more cumbersome postprocessing and longer run times than the same problem simulated using the lake package.
authors.affiliation: Department of Geology and Geophysics, University of Wisconsin-Madison, 53706, USA. andy@geology.wisc.edu
authors.forename: Mary P
authors.initials: MP
authors.lastname: Anderson
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Hunt
authors.forename: James T
authors.initials: JT
authors.lastname: Krohelski
authors.forename: Kuopo
authors.initials: K
authors.lastname: Chung
mesh_terms: D008962:Models, Theoretical; D012987:Soil; D014872:Water Movements; D014881:Water Supply
chemical_list: D012987:Soil