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Title: VALIDATION OF WEPP SEDIMENT FEEDBACK RELATIONSHIP USING SPATIALLY DISTRIBUTED RILL EROSION DATA

Author
item Zhang, Xunchang
item LI, ZHAN-BIN - *ISWC-YANGLING, PRC
item DING, WEN-FENG - *ISWC-WUHAN, PRC

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 8/4/2005
Citation: Zhang, X.J., Li, Z., Ding, W. 2005. Validation of wepp sediment feedback relationship using spatially distributed rill erosion data. Soil Science Society of America Journal. 69:1440-1447.

Interpretive Summary: Process-based soil erosion models are not thoroughly validated due to the lack of spatially distributed soil erosion data. The objective of this work was to evaluate the effects of sediment load on soil detachment in the concentrated rill flow using distributed rill erosion data derived with Rare Earth Element (REE) tracers. Four REE oxide powders (Ce, Nd, Sm, and Dy) were separately mixed with a loessial silt loam soil, and each mix was packed in an 1-m segment in a 4-m flume. Each newly packed flume was subjected to flow scouring at a selected slope and inflow rate for about 15 min. Three slopes (10.5, 15.8, and 20.2%) and five inflow rates (2.5, 3.5, 4.5, 5.5, and 6.5 L min-1) were used, and two replicates were made for each combination. Runoff and sediment samples were collected at 1- or 2-min intervals. Flow velocity and width were monitored. Sediment samples were analyzed for REE compositions by Instrumental Neutron Activation Analysis (INAA). The REE concentrations in each sediment sample were used to estimate soil losses from each tagged segment. Results showed a general linear trend that rill detachment rates decreased as sediment loads increased in the downslope direction. These results further indicated that the reverse linear relationship between sediment load and soil detachment as assumed in the Water Erosion Prediction Project (WEPP) model is approximately valid for simulating rill erosion. This work will be useful to erosion modelers to validate and refine process-based erosion models.

Technical Abstract: Process-based soil erosion models are not thoroughly validated due to the lack of spatially distributed, instantaneous rill erosion data. The objective of this study was to validate the sediment feedback relationship of the Water Erosion Prediction Project (WEPP) model using distributed instantaneous rill erosion data derived with Rare Earth Element (REE) tracers. Four REE oxide powders (Ce, Nd, Sm, and Dy) were separately mixed with a loessial silt loam soil, and each mix was packed in a 1-m segment in a 4-m flume. Each newly packed flume was subjected to flow scouring at a selected slope and inflow rate for about 15 min. Three slopes (10.5, 15.8, and 20.2%) and five inflow rates (2.5, 3.5, 4.5, 5.5, and 6.5 L min-1) were used, and two replicates were made for each combination. Runoff and sediment samples were collected at 1- or 2-min intervals. Flow velocity and width were monitored. Sediment samples were analyzed for REE compositions by Instrumental Neutron Activation Analysis (INAA). The REE concentrations in each sample were used to estimate sediment deliveries from each tagged segment. There existed a trend that net rill detachment rates decreased linearly as sediment loads increased in the downslope direction. The slope of regression (rate of the decrease)became more negative with inflow rates at the 10.5% slope, but became less negative at the 20.2% slope. These results show that the assumed sediment feedback relationship in the WEPP model is approximately valid for simulating rill detachment by downward scouring and rill head cutting.