APPROXIMATE CONVECTION DIFFUSION WAVE METHOD TO COMPUTE DISCHARGE USING ONLY STAGE DATA

Abstract

Measuring discharge in a river system involves tedious procedures. Over the last few decades, innovations in technology has improved discharge estimation methods in rivers due to the use of improved velocity measurement equipment, such as the ADCP and, thereby, easing and improving the discharge estimation at the river gauging sites. However, adopting these technologies prove to be expensive for its use in very many sites of the rivers due to the high cost of such equipment. To overcome this expensive approach of river discharge estimation, an alternative approach of discharge estimation based on the use of an equation developed using hydrodynamic principles to estimate discharge using only the observed stage data at a river site is proposed in this study. The governing equation of the proposed model in this study is based on the use of Approximate Convection-Diffusion wave (ACDW) equation combined with the Diffusive Wave model. This method can be considered as a more generalized approach ideally suited for field applications. Due to its simplicity, easy applicability, versatility and accuracy of estimating discharge for a wide range of roughness and channel bed slope conditions, this method can be considered ideal for field applications. Moreover, the method can be applied to estimate discharge in a channel characterized by varying cross-section or the roughness parameter along the river reach. The proposed method has been first tested for a number of hypothetical flood scenarios in hypothetical channels. Further its accuracy, and its applicability has been evaluated using the well-established evaluation criteria such as overall reproduction of benchmark discharge hydrograph, peak error and the volume error. After its evaluation using hypothetical flood scenarios in hypothetical channels, the field applicability of the method is evaluated by applying the method for the natural river gauging sites to estimate discharge using only the observed stage data at the desired site. The limitation of the method arises due to uncertainty of the used Manning’s roughness coefficient(s) at the desired gauging site and when the section-control of the gauging site is lost to the channel control of the considered channel reach of the gauging site. Therefore, to avoid this problem it may be prudent to carry out the sporadic velocity measurements at the desired river site during the passage of a flood wave, for the confident use of the proposed model or formula for estimating discharge using only the stage data.