Climate change has posed many threats including extreme floods that may cause huge damages to the existing dams. There are many old dams which were designed on the basis of empirical formulas in absence of reliable rain gauge and river gauge data as in those days the limitations of instruments for observation of hydrological behavior of rivers were ample. Frequent extreme events with severity have proven the limitations of the then applied empirical formulas for designing the spillover capacities of the dams and hence has become urgent to review the hydrology for such dams. This paper discusses this issue with the help of a case study of Gujarat, india in which has been the discussion on one river basin having two river courses meeting somewhere on the approach of the plane land. The said river courses have a dam on each. This basin called Banas is an interstate basin shared by Gujarat and Rajasthan states of India. It received heavy flood after construction of a dam on one course for which the design flood was computed as per an empirical formula but the actual flood with much higher discharge occurred soon after its construction and hence the review of hydrology was made as per which additional spillway was subsequently provided to ensure the safety of the dam. Another dam was constructed on the other course of the same basin with the revised historical flood as the basis for computation of spillover capacity; however, the recent flood proved that the scientific approach for the latter case and that, too, with the revised fold data fell short in estimating the safe design flood. Albeit, the previously constructed dam with added spillover capacity not only performed well but also helped modulate the flood peak effectively. Thus, this paper puts forth an interesting case study as to how the flood estimation methodologies are required to be modified in the present times of unexpected extreme floods in order to ensure effective flood control and safety of the dams. It also underlines the importance of retrofitting of the existing old dams in light of the recent flood data by reviewing the hydrology.
