Year Established: 2017 Start Date: 2017-03-01 End Date: 2019-02-28
Total Federal Funds: $7,144 Total Non-Federal Funds: $13,848
Principal Investigators: Achilleas Tsakiris, Thanos Papanicolaou, Jon Hathaway
Abstract: Sediment rating curves, which are relations between sediment transport rates and water flow often exhibit large degrees of variability, which limits their predictive ability. This variability is typically the outcome of the hysteresis, or time lag, between the water discharge hydrographs and the sediment transport fluxes. The type and magnitude of hysteresis is controlled by the amount as well as the timing of the supplied sediment from upstream and lateral sources relative to the water flow changes during the rising and falling limbs of a storm hydrograph. The variability in rating curves due to hysteresis is accentuated by changes in water temperature, which the fall velocity of sediment, and thus their transport mode, i.e., suspension or bedload. However, the effects of water temperature on sediment rating curves still remain poorly documented. Variability in sediment supply relative to the water flow in the state of Tennessee is often attributed to changes in land management practices in agricultural landscapes that profoundly affect the amount and timing of sediment delivery in rivers, as well as to the encroaching urbanization that leads to a decrease of sediment inputs and increase of runoff into urban rivers. More importantly, the dams and reservoirs in many Tennessee rivers limit sediment supply to the downstream reaches, while simultaneously increasing the flashiness of sediment supply during water releases. These factors are further promoted by the global climatic change that is expected to increase the chances of excessive rainfall amounts. An improvement of the predictive ability and reduction of the uncertainties of sediment rating curves due to the hysteresis phenomenon is necessary for the design and management of reservoirs, as uncertainties in sediment rating curves translate to inaccurate boundary conditions of predictive sediment transport models and errors in estimates of reservoir size and dam lifetime using these predictions. Along the same lines, accurate sediment rating curves are needed for training the morphodynamic numerical models used for designing and placing hydraulic structures, such as bridge piers and bank protection countermeasures. Further, reduction of the uncertainties in sediment rating curves is needed for water quality assessment, and quantification of the contaminant loads attached to sediment particles, as well as for designing stream restoration practices. This research will involve the installation of a monitoring station that tracks the movement of sediment and the water temperature in an urban stream. The information that will be gathered on the sediment particle travel timing and water temperature monitoring will be combined with simultaneous measurements of key hydraulic parameters for characterizing the hysteresis in the sediment rating curves for different storm hydrographs and supply conditions and with varying water temperature. These additional parameters will be retrieved from the Second Creek Observatory operated by the University of Tennessee in the city of Knoxville, TN. The knowledge that will be gained from this monitoring will be used to characterize the hysteresis phenomenon for various hydrologic and sediment supply conditions and be applied for improving the reliability of sediment rating curves.