- Sediment transport,
- Ems River Estuary (Germany and Netherlands)
We present measurements which show that the tidal Ems River in Germ any is extremely muddy over a 30 km + turbid zone, with fluid mud o f 1-2 m thickness covering the bed with suspended sediment concentrations (SSC) o f greater than 50 kg.m-3. Moreover, we show that these elevated SSC contain large quantities of organic material which deplete dissolved oxygen (DO) and produce summertime hypoxic zones. Using mathematical modeling, we develop simplified representations o f the estuary physics that reproduce the tidally-averaged circulation, SSC distribution, and oxygen depletion. These models show that SSC and oxygen concentrations are extremely sensitive to factors such as the mean depth, the mixing due to bottom friction (turbulence), and river flow. The observed increase in SSC and decrease in DO over the past 25 years is linked to the progressive deepening o f the tidal Em s from 4-5 m to 7 m between 1985- 1994, which moved the turbid zone upstream and decreased mixing. A review of scientific literature and data from the Em s suggests that hum an intervention (dyking,channel modification) combines with more gradual natural changes (sea level rise, climate variation) to continually modify sediment transport.