Changes in Suspended Sediment Transport in the Town Creek Watershed: Interpretation of Sediment Rating Curves

Ramirez-Avila, J. J., McAnally, W. H., Langendoen, E. J., Ortega-Achury, S. L., & Martin, James L. (2011). Changes in Suspended Sediment Transport in the Town Creek Watershed: Interpretation of Sediment Rating Curves. 2011 NGI Annual Conference. Mobile, AL: Northern Gulf Institute.

Sediment rating curves, in the form of a power function, represent the relationship between suspended sediment load and water discharge in a stream. This study examines the characteristics of sediment rating parameters recorded at the USGS station 02436500 (Town Creek near Nettleton, MS) between 1981 and 1995 and between May 2008 and May 2009. Temporal analysis of suspended sediment transport relations showed a reduction in the amount of annual suspended sediment loads contributed by the Town Creek watershed at a specific instantaneous flow. A significant correlation (=0.05) and an exponential expression with a negative slope were determined between the suspended sediment load at low or base flow conditions (sediment rating curve coefficient) and the rate of increase in load (sediment rating curve exponent). A significant increase in the relative efficiency of the Town Creek to transport increasing amounts of suspended sediment with increasing flow rates occurred over time, evidencing the high erosion potential of important geomorphic processes in a specific area of the watershed. A temporal reduction of suspended sediment loads at low flow conditions (sediment rating curve coefficient) was simultaneously observed. Both conditions can be explained by the difference in stages of channel evolution presented in different sections along the Town Creek. The increase in time of the sediment rating curve exponent reflects stream channels that transition from Stage III toward the Stage IV in the conceptual channel evolution model. The suspended sediment transport rating curves obtained for different periods at the studied location within the Town Creek watershed, describes a sediment delivery directly produced by streambanks with a trend toward the increase of the sediment supply. However, the reduction in time of the sediment loads evidences that this sediment delivery is predominantly supplied by specific areas from the headwaters reaches within the watershed, and after a specific zone, the variation in land use and channel characteristics (vegetation, slope, area, shape) are favorably reducing the sediment export of the Town Creek watershed.