A WATER-BUDGET APPROACH TO HYDROLOGIC RESTORATION OF A SEDGE FEN

A vast, ground-water-supported sedge fen in the upper peninsula of Michigan was ditched in the early 1900s in a failed attempt to promote agriculture. Dikes were then constructed to impound seasonal sheet surface flows for waterfowl management. The U.S. Fish and Wildlife Service, which now manages the wetlands as part of Seney National Wildlife Refuge, sought to reduce ground-water losses caused by the ditches, reduce erosion of peat and underlying sand in the primary ditch, and redirect water flows without harm to downslope lands. A water budget was developed for the large C-3 impounded pool that serves as the central receiving and distribution body for water in the affected wetland. Surface-water inflows and outflows were measured in associated ditches and natural streams, ground-water flows were estimated using a network of wells and piezometers, and precipitation and evapotranspiration components were estimated using local meteorological data.

The input data and resulting water budget were used to calculate changes in inflows to the C-3 pool that would result from blocking or redirecting upslope ditches. Required releases of water from the C-3 pool were then determined with recognition that downslope flows via the primary ditch must be reduced to halt erosion and the ditch would be dammed to halt ground-water losses below the pool. Control structures were then designed to release water from the C-3 pool via abandoned historic natural channels such that they would not exceed channel capacity. Finally, potential changes in ground-water supply to the wetland downslope from the pool were determined.

Ecological studies of pre-restoration conditions were conducted, and the Refuge has since begun to implement construction activities. Potential new beaver dams are an additional factor that could not be addressed in pre-restoration planning, but they could have major effects on both wetland ecology and hydrology. Follow-up studies in future years will address the dams and their modifications of the restored wetland.