|LOPES, V. - UNIVERSITY OF ARIZONA
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2002
Publication Date: 4/1/2004
Citation: Canfield, H.E., Lopes, V.L. 2004. Parameter indentificationin a two-multiplier sediment-yield model. Journal of the American Water Resources Association 40(2):321-332.
Interpretive Summary: In order to improve our ability to predict where and when soil erosion occurs on a watershed, we have to be able to identify what types of erosion mechanisms predominate at different places on the watershed. In general, two mechanisms control sediment production and delivery from a small watershed: sediment eroded by raindrop impact and sediment eroded by flowing water. The difficulty is to determine which mechanism is primarily responsible for entraining the sediment load at the watershed outlet where sediment is typically measured.By applying the KINEROS2 runoff-erosion model to a small watershed for different-sized events, we concluded that the relative contributions from these processes can be determined for events that occur once every three years or so, but not for smaller events. We also found that the sampling frequency of sediment discharge during the storm has an effect on differentiating these two mechanisms in the modeling gprocess. If sediment samples are not collected with sufficient frequency, the KINEROS2 model will not be able to distinguish between the two erosion mechanisms, even for large events. Therefore, depending on the storm characteristics and sediment sampling frequency during the storm, it is possible to determine where and when erosion occurs on a watershed using a runoff-erosion model like KINEROS2. These findings should improve our understanding of the impacts of management practices and climate change on watersheds, and our ability to prevent and control soil erosion.
Technical Abstract: A process-based, distributed runoff-erosion model (KINEROS2) was used to examine problems of parameter identification of sediment entrainment equations for small watersheds. Two multipliers were used to reflect the distributed nature of the sediment-entrainment parameters: one multiplier for a raindrop-induced entrainment parameter, and one multiplier for a flow-induced entrainment parameter. The study was conducted in three parts. First, parameter identification was studied for simulated error- free data sets where the parameter values were known. Second, the total number of data points in the simulated sedigraphs was reduced to reflect the effect of temporal sampling frequency on parameter identification. Finally, event data from a small rangeland watershed were used to examine parameter identifiability when the parameter values are unknown. Results demonstrated that while unique multiplier values can be obtained for simulated error-free data, unique parameter values could not be obtained for some event data. Unique multiplier values for raindrop-induced entrainment and flow-induced entrainment were found for events with greater than a two-year return period (~25mm) that also had at least 10mm of rain in ten minutes. It was also found that the three-minute sampling frequency used for the sediment sampler might be inadequate to identify parameters in some cases.