Shallow ground-water flow and drainage characteristics of the Brown ditch basin near the East Unit, Indiana Dunes National Lakeshore, Indiana, 1982

Brown ditch consists of several segments that drain wetlands between dune ridges near the East Unit of Indiana Dunes National Lakeshore in Porter County, Indiana, west of Michigan City.The dune ridges were formed during higher stages of Lake Michigan in the Pleistocene and Recent Epochs.Surficial lacustrine sands deposited during these older lake stages form a water-table aquifer that provides perennial base flow to the ditch.The northwest-trending reach of the ditch immediately upstream from the lakeshore and the upstream east arm south of the adjacent town, The Pines, were dredged in the summer of 1983.Profiles established before the dredging in July and August 1982, showed the average streambed slope of the ditch in the lakeshore (0.19 percent) to be six times that of the upstream east arm (0.03 percent) at that time.The ditch contains debris and vegetation in the reach in the lakeshore but seems to convey all the base flow it receives there.In contrast, before the dredging the upstream east reach contained several ponded sections where flow was sluggish.Water-table declines for hypothetical reconstructions of the ditch were estimated by using a digital model to compute changes in the boundary component of the water-table head.Dredging to eliminate high points to form uniformly graded streambed and stage profiles in the upstream east arm could lower the water table in The Pines 0.2 to 2.0 feet.Dredging to lower the ditch stage in the lakeshore by 0.5 to 1.0 foot would cause additional water-table decline of less than 0.5 foot in The Pines.However, dredging in both the lakeshore and the upstream east arm could lower the water table by nearly 1.0 foot within the lakeshore.