The increasing economic importance ofwaterside development in many cities has been the driver for major investment in barrage construction in the U.K. To ensure the sustainability of these structures it is crucial to understand their impact on sedimentation distribution and re-distribution patterns. As sedimentation is essentially a long-termphenomenon, forecasting of impoundment behavior using a computer model is necessary. This paper presents the results of a computer simulation of long-term (50 year) sediment distribution predictions for the Tees barrage impoundment, a total exclusion barrage built in 1994 and situated in the north-east of England, U.K. The simulations were undertaken using the one-dimensional "ISIS Sediment" modeling software. The upstream boundary conditions, in terms of both flow and sediment, were estimated from data collected on the river at Low Moor, and take account of possible sediment source changes during the 50 year simulation period. The predictions from the model show that after 30 years the impoundment reaches a state of dynamic equilibrium irrespective of sediment supply.