Flow measurement is critical in hydraulic engineering for developing and managing water resources. The mean flow velocity and cross-sectional flow area at the measurement location are two major metrics required for discharge estimation. River bathymetric surveys or advanced technologies such as the Acoustic Doppler Current Profiler (ADCP) might be used to determine the cross-sectional area. The mean flow velocity can be measured using different techniques depending on whether the measurements are taken from a distance (non-contact) or a contact method (traditional approach). Non-contact velocity measuring techniques are becoming increasingly common in recent years since they are less time-consuming and easier to utilize while dealing with heavy flows and inclement weather. One such modern approach is the entropy-based concepts (such as Shannon entropy, Tsallis entropy and Renyi entropy) used to calculate the discharge from non-contact observations, yielding superior results to classic approaches such as the velocity area method. Entropy-based velocity distribution depends on the crucial parameter called entropy parameter (a function of the ratio of the mean and maximum velocity), which is linked to the channel and flow characteristics. Its value is surmised to be constant for a particular river reach. Due to this fact, the entropy-based approach was used in this study to evaluate the discharge in case of the adverse bed slope condition that may arise due to several reasons, and one among them is the excessive mining in the particular river reach. This study collected the experimental velocity data for the mild, horizontal and adverse bed slope conditions from a rectangular flume fitted with a mechanical apparatus to change the bed slope. Results concluded that the mild and horizontal slope conditions depicted only a slight variation in entropy parameter value, i.e., almost constant. The same was adopted for finding the mean velocity for the adverse bed slope condition to calculate the discharge. Furthermore, the discharge error analysis presented a substantial justification for the utilized single constant value of the entropy parameter for the whole cross-section, and the same can be employed for future explorations on the same channel stretch.