Analysis and simulation of large erosion events at central Texas unit source watersheds

- Up to 50 year daily erosion records were examined at five unit source watersheds.
- The upper ten percent of erosion events deliver about half of long term masses.
- Empirical and physics based erosion simulations were performed with the SWAT model.
- Both models performed similarly in terms of long term masses delivered.
- Physics based routines provided a more realistic distribution of event magnitudes.

SummaryThis study uses long-term daily sediment records (12-51 years) from 5 unit-source watersheds in central Texas to examine the role of large infrequent erosion events in the makeup of the overall soil loss record. Additionally, multi-decadal daily erosion simulations with the Soil and Water Assessment Tool (SWAT) using both the Modified Universal Soil Loss Equation (MUSLE) and physics based erosion routines are conducted to assess the routine's ability to predict extreme events and long-term budgets. The empirical record indicates the upper 10% of erosion events (in terms of mass) comprise roughly half of the long-term soil loss sum. These upper end events are characterized by large unit flow erosion values and not necessarily associated with precipitation or runoff extremes. The two SWAT routines showed little differences in total soil loss masses; however, the distribution of soil loss events from the physics based simulation, including upper end events, more closely resembled the empirical record than the MUSLE prediction.