UVM Theses and Dissertations
Format:
Print
Author:
Tyler, Josh
Dept./Program:
Civil and Environmental Engineering
Year:
2014
Degree:
M.S.
Abstract:
A temporal rise in the anthropogenic nutrient input to freshwater bodies and tributaries in the form of phosphorus (P) has deteriorated the quality ofwater resources and the health of aquatic ecosystems throughout the United States. Excessive P input promotes eutrophication and in the Lake Champlain Basin, Vermont, multiple segments of Lake Champlain, such as St. Albans Bay are identified as eutrophic. Nonpoint source P generated by agricultural runoff is typically dominated by sediment bound P and has been identified as a major P input to St. Albans Bay. Topographical variability at the field scale can lead to increased overland flow during storm events generating greater scouring and sediment mobilizing potential. The increased sediment transport potential of topographical variability is exacerbated by greater intensities of precipitation over shorter periods along with an increased number of wet days experienced overagricultural growmg seasons.
The Water Erosion Prediction Project (WEPP) and the Soil Water Assessment Tool (SWAT) were applied to simulate runoff and sediment yield at the field scale in the St. Albans Bay watershed. The models were run and the simulated outputs were compared with measured runoff and sediment yield values. Storm intensity and duration were increased over the simulated events as well as the curve number (CN) value to SWAT. Drastic differences were noted in simulated sediment transport between the two models. Significantly higher sediment yield was observed from SWAT outputs upon increase in the duration and intensity of storm events as well as from an increase in the empirical CN input as compared to the WEPP outputs. Three 24-hour rain events were quantified for total sediment (TS), total suspended solids (TSS), total P (TP) and sediment bound P (TSS(P)).
Results indicate that an increase in the concentration of TSS generates an increase in the concentration of TSS(P) and the frequency at which a wet day followed a wet day over the three storm events greatly influences the generation of TS and TSS. The variability in topography, non-uniform soil characteristics, and intensity and duration of a storm event at a subwatershed field scale are paramount in the quantification of agricultural runoff, sediment yield, and non-point P transport. WEPP uses a more mechanistic approach that incorporates topographic details, while SWAT uses an empirical approach that ignores small-scale topographic heterogeneity. As such, due to generalization of topographical variability and a combined approximation of runoff and erosion WEPP is a more appropriate model for the simulation of the subwatershed field site.
The Water Erosion Prediction Project (WEPP) and the Soil Water Assessment Tool (SWAT) were applied to simulate runoff and sediment yield at the field scale in the St. Albans Bay watershed. The models were run and the simulated outputs were compared with measured runoff and sediment yield values. Storm intensity and duration were increased over the simulated events as well as the curve number (CN) value to SWAT. Drastic differences were noted in simulated sediment transport between the two models. Significantly higher sediment yield was observed from SWAT outputs upon increase in the duration and intensity of storm events as well as from an increase in the empirical CN input as compared to the WEPP outputs. Three 24-hour rain events were quantified for total sediment (TS), total suspended solids (TSS), total P (TP) and sediment bound P (TSS(P)).
Results indicate that an increase in the concentration of TSS generates an increase in the concentration of TSS(P) and the frequency at which a wet day followed a wet day over the three storm events greatly influences the generation of TS and TSS. The variability in topography, non-uniform soil characteristics, and intensity and duration of a storm event at a subwatershed field scale are paramount in the quantification of agricultural runoff, sediment yield, and non-point P transport. WEPP uses a more mechanistic approach that incorporates topographic details, while SWAT uses an empirical approach that ignores small-scale topographic heterogeneity. As such, due to generalization of topographical variability and a combined approximation of runoff and erosion WEPP is a more appropriate model for the simulation of the subwatershed field site.