On the other hand, the multi-criteria compromise solutions provided improved input–output performance in terms of measures not used in calibration, with generally more consistent behavior across calibration and evaluation years, while maintaining physically realistic a priori values for most of the model parameter estimates adjustments were found to be necessary for only a few key model parameters. Moreover, although unconstrained optimization performed best (as measured by the calibration criteria), poor hydrograph simulation performance was evident when evaluated in terms of multiple performance statistics not used in the calibration.
Our results indicated that whereas simulations using the a priori parameter estimates give consistently positive flow bias, unconstrained optimization to the response data results in parameter values that are very different from the a priori parameter set. We demonstrate the method by examining the extent to which a priori parameter estimates specified for the Hydrology Laboratory’s Research Distributed Hydrologic Model (via a set of pedotransfer functions) are consistent with the optimal model parameters required to simulate the dynamic input–output response of the Blue River basin. This paper proposes a Maximum Likelihood multi-criteria penalty function strategy for evaluating a priori parameter estimation approaches. However, such methods are typically based on local-scale process understanding and simplifying assumptions and an increasing body of evidence suggests that hydrologic models that utilize parameters estimated via such approaches may not always perform well. Further study should include hypothesis testing in a variety of material both homogeneous and heterogeneous.Ī priori parameterization approaches that improve our ability to provide reliable hydrologic predictions in ungauged and poorly gauged basins, as well as in basins undergoing change are currently receiving considerable attention.
One feels that a return to the stream would be a healthy complement to flume measurements. Interestingly, earlier work on river meandering was the product of long days in the field in more recent years such research has been undertaken in the laboratory. Most of its intricacies have been learned through laboratory flume experiments. Theories for meandering do not clearly explain the cause of helicoidal flow.
The characteristics of helicoidal flow seem to be the best explanation for the development of meanders. Prevalent ideas concern meandering as being dependent not only on stream flow but also on the rate of stream discharge, sediment load, size and type of sediment, channel roughness, depth, width, velocity of flow, and quality of water itself. The purpose of this paper is to review and analyze selected meander theories that contribute either directly or inherently to current meander concepts which revolve around the effect of helicoidal flow. Foremost among these is the effects of helicoidal flow within the stream flow. Several explanations (derived from both field and laboratory flume) have been advanced to account for stream meandering, among them being the earth's rotation, excess current energy, transverse oscillations, initial current deflection, local disturbances, changes in stages of discharge and bed load and helicoidal flow. Meandering is one of the most complex problems associated with the behavior of rivers.
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