Application of gradually-varied flow algorithms to simulate buried streams

This paper reports the underlying algorithm, implementation, and development details of the Flow Analysis of Buried Streams (FABS) hydraulic model. This model simulates water surface profiles for 1-D non-Darcy flow through buried streams. Buried streams are formed in open-pit coal mines due to the disposal of large volumes of coarse rockfill. In such buried streams the formerly open channel passes through very coarse porous media but the behavior of this flow does not follow Darcy's law. Rather, it behaves in a manner similar to that of ordinary open channel flow. The longitudinal variation in the depth of water along the stream is not, however, governed by the roughness of the stream-bed, but by the characteristics of the coarse porous media that now fills the channel. Such flow is governed by non-Darcy flow operating under the Dupuit assumptions. The performance of the model in simulating steady non-Darcy flow profiles was evaluated under laboratory experimental conditions and found to be satisfactory. The model uses either Wilkins' or Stephenson's equation to compute head losses. It was found that these equations performed equally well in simulating experimental water surface profiles. The performance of the model was also evaluated under three different friction-slope averaging methods, namely, the arithmetic, geometric, and harmonic average. Based on the results obtained in this study, it is suggested that any of these frictions-slope averaging techniques result in satisfactory flow profiles, provided that reach lengths are not excessive. Although there are certain limitations and definite possibilities for further improvement, it is believed that the FABS model represents a significant step forward in providing more explicit assistance in the non-Darcy water surface profile simulation process.