The purpose of the investigation is to provide a means to assess the impacts on surface-water hydrology due to changes in land use resulting from surface mining of coal in the Fort Union Coal Region, North Dakota and Montana. The objectives of the study are to: (1) Determine premining hydrologic conditions in small representative drainage basins and provide historical data with which to compare the magnitude of changes resulting from mining, and (2) develop the capability of making reasonably accurate projections of hydrologic effects resulting from the various land-use changes caused by surface mining. Data collection has been underway since October 1976 for the West Branch Antelope Creek study area in western North Dakota and since March 1978 for the Hay Creek study area in eastern Montana. Data collected during the premining period are being analyzed using statistical methods for the evaluation of the premining conditions. A digitial model with the capability of making hydrologic projections is being developed. Most of the model components have been tested during 1979 and 1980. (USGS)