Hydrologic Characteristics of a Managed Wetland and a Natural Riverine Wetland along the Kankakee River in Northwestern Indiana

Abstract

Characteristics of ground-water/surface-water interactions were identified at a managed wetland (Hog Marsh) and a natural riverine wetland (LaSalle) located on the north and south sides, respectively, of the Kankakee River in northwestern Indiana. Hog Marsh covers about 390 hectares of the Grand Kankakee Marsh County Park. LaSalle covers about 100 hectares of the LaSalle State Fish and Wildlife Area, and is about 20 kilometers downstream of Hog Marsh. Hydrologic characteristics of the two wetlands were investigated using data from 1997 to 1999 for 22 wells adjacent to the Kankakee River in northwestern Indiana. Surface-water levels at the managed wetland were controlled by a system of channels, levees, and managed flooding. Surface-water levels at the natural riverine wetland were not controlled. Ground-water levels in the unconfined surficial aquifer beneath the two wetlands were analyzed by assessing water-level fluctuations. Fifteen wells at Hog Marsh and seven wells at LaSalle were monitored. The interquartile range in ground-water levels away from the river at Hog Marsh fluctuated less (from 0.4 to 0.7 meters) than all ground-water levels in the same aquifer beneath LaSalle (from 0.9 to 1.0 meters). The difference in the range of water-level fluctuation probably is attributable to the managed flooding of Hog Marsh units, which tends to maintain somewhat uniform water levels in that wetland. Ground-water-flow directions along a vertical section through the unconfined surficial aquifer at the managed wetland were more variable than those at the natural riverine wetland. During winter and spring, when flow in the Kankakee River is high, flow is from the Kankakee River into the adjacent surficial aquifer and towards a 2-meter-wide Brown Ditch on the north side of Hog Marsh. Water levels in Brown Ditch remain lower than those in the Kankakee River during this period. From June to December, when flow in the Kankakee River is moderate to low, a flow divide developed near the center of the managed wetland. Ground-water flow south of the divide is to the Kankakee River; north of the divide, it is toward Brown Ditch. Slight ground-water mounding near the center of the managed wetland is accentuated by water-management practices that intentionally flood that area. Ground-water flow in the surficial aquifer at the natural riverine wetland was not impeded by ditches or managed flooding, and a simple flow-through system from areas south of the Kankakee River to the river was observed. A ground-water flow model was constructed along a representative cross section through the surficial aquifer at the managed wetland and calibrated using data collected at the site. A no-flow boundary was used beneath the Kankakee River, and head-dependent boundaries were used along the north end of the model and at the base of the model. The model simulations indicated that artificial controls on the managed-wetland hydrology create sites of recharge to and discharge from the surficial aquifer that are absent at the natural riverine wetland. The steady-state flow simulation represented flow conditions following a 4-month period of no changes in hydrologic stresses. The simulation results indicated that flow paths originating from flooded areas near the center of the managed wetland are sources of aquifer recharge during the managed-flooding period. Brown Ditch captured almost all of the ground water north of the managed wetland. The simulated water budget along a well transect indicated that 88 percent of inflow to the surficial aquifer beneath the managed wetland was from a distribution channel and from flooding in the management units. These modeling results identify differences in flow patterns between the managed and natural riverine wetlands in addition to those identified by the water-level data. Results of transient simulations indicated that surface water from the Kankakee River penetrated only about 2 to 3 meters into the surficial aquif