Approximately 1100 miles of stream reach on 19 rivers have been designated as scenic waterways in Oregon since 1970. Collectively, these reaches drain about 43% of the state’s surface area. New water rights are not allowed in scenic waterways if they diminish the flows necessary to support fish, wildlife, or recreational uses. Because Oregon law recognizes an interconnection between surface and ground water, scenic waterway statutes limit new ground-water rights as well as surface-water rights. New ground-water rights are allowed unless scenic waterway flows are not being met and the new uses cumulatively reduce stream flows more than 1% of the average daily flow or 1 cfs, whichever is less. The Water Resources Department reviews all new ground-water applications to determine the potential impact to scenic waterway flows. Because surface-water availability is tracked on a monthly basis, impacts to scenic waterway flows are assessed for each calendar month. Since appropriate numerical models are only available for several basins, the department has developed an analytical spreadsheet model to estimate the monthly stream depletion at steady state caused by well withdrawals. The model is based on a transient analytical solution developed by Hunt (1999) for a partially penetrating stream with a streambed clogging layer. Monthly pumping is normalized to local crop consumption and superposition is used to determine cumulative pumping and residual impacts for each month in the last year of a user-specified pumping duration. Steady state is attained when the overall model residual approaches zero. To reduce model run time, the distribution of residuals at steady state is estimated using the monthly distribution of residuals between the first and the maximum specified year of pumping. A 25-year model run is generally sufficient to provide a good estimate of residual distributions at steady state.