The impacts of climate change on river basin in mountainous region range from the accelerated erosion, increasing intensity of natural disasters and affecting agriculture to further endangering food security (beniston, 2003; beniston et al., 2007; briscoe & malik, 2006). due to occurrence of extreme rainfall event during june 2013 in uttarakhand; average 1000% of normal rainfall (sandrp, 2013) & jammu-kashmir during june to sept 2014 it was recorded 100-200 % of normal rainfall (imd, 2014). in above context, the water inflowing to the reservoir is uncertain. if the rainfall intensity augmented significantly, the reservoir water will increase rapidly. this condition can cause overtopping and further imperil the dam. a review reported by the corps of engineers u.s. army (usace) showed that 36 % of dams are unsafe in which 80% due to inadequate spillway capacity (suprapto, 2013). man-made catastrophe focused much needed attention on the importance of adequate spillway design capacity. to increase the spillway capacity is often by additional construction of spillway (asdso, 2013). however, these efforts are often obstructed due to field conditions that do not support such option. in many cases, modification to the existing spillway may be a better alternative. these conventional barrages have limited discharging capacity & are incapable to handle extreme flood events. usually head over crest cause submergence and also diminish weirs efficiency. thus, in view of climate change, hydraulically much more efficient spillways are required to be developed to ensure safety of existing & new dams. increasing specific flow form hydraulic structures is one of the thought of spillway rehabilitation. labyrinth weir may be used for amplifying specific flows of existing spillway. sediment trapping behind labyrinth weir might be one of the disadvantages for river with high sediment flow. the piano key weir (pkw), ramped type labyrinth weir is a hydraulically attractive alternative to linear overflow weirs, increasing the unit discharge for similar heads and spillway widths. this advantage allows operating dam reservoirs on an increased level and provides thereby an enhanced retention volume. it is a result of the non-linear nature of pkw being folded back and forth to make repeated cycles or keys. this type of weir is particularly suitable for sites where topographic conditions limit the extent of its width. together with its high discharge capacity for low heads, this geometry makes these weirs interesting in spillway rehabilitation. this paper investigates the recent developments to improve hydraulic competence of spillways. head reduction over crest can improve efficiency as well as reduce submergence. this study shows that for increasing discharge, head reduction with respect to conventional rectangular weir is reducing but reduction was found above seventy percent for all the experiments.