SEDIMENT DYNAMICS AND TRANSPORT: A FLUVIO-GEOMORPHIC ASSESSMENT OF GULLY EROSION IN THE TEXAS BLACK-LANDS USING SWAT-LTE FOR PREDICTING HEAD-CUT RETREAT

Gully erosion alters the landscape throughout the Black Land Prairies in Texas, impacting agriculture. Categorically, gullies are either ephemeral or classical, a distinction based on their spatio-temporal distribution. A gully forms by concentrated flow erosion, reinforced by antecedent conditions or when the hydraulic shear stress applied to the bed exceeds some critical threshold. The Food and Agricultural Organization estimates that billions of dollars are spent annually to mitigate the impacts of gully erosion. Stream and riverine impairment, reservoir siltation, reduced agricultural productivity, and pollution are exacerbated due to sediment loss, and degradation in gullies. Griener (1982) estimates that gully and stream bank erosion contributes 98 million tons of sediment per anum within the State of Texas. Because of the stochastic nature of gullies and the ranging perturbations reinforcing incipient motion in these sedimentary systems, there is a need for time series modeling.

The El Nino season provided the ideal confluence of atmospheric conditions for analyzing gully migration in Texas. This poster seeks to elucidate on whether storm based migration rates can act as a valid proxy for modeling long term gully migration. Structure from motion is examined as a tool for capturing morphological changes within gullies. The predictive ability of the Soil Water Assessment Tool LTE (SWAT-LTE) was used for model parameterization.

Monitoring consisted of the use of a 2.5 foot H Flume, tipping bucket rain gauge, and the Trimble R8 GNSS Kinematic GPS for precise surveying of the head-cut apex. A digital camera was used for morphological analyses. Soil erodibility was assessed using the Submerged JET Test. 5 storms events were used for model calibration and sensitivity analyses. Historical aerial photographs were used for model validation.