Formulating the spring discharge-function for the recession period by analyzing its recession curve: A case study of the Ranichauri spring (India)

The Greater Himalayan region is witnessing a changing rainfall pattern from the last few decades. Low-intensity longer-duration rainfall events have now been replaced with intense and shorter-duration events that are further responsible for the reduced recharging of the spring catchments. Consequently, the natural springs are either drying up or becoming seasonal. Prediction of spring water availability during the recession period is the key to its proper management. The spring discharge-rate can be forecasted by studying its behaviour for the past recession periods. Expressing recession curve in mathematical terms requires its quantitative analyses in priori . It was found that the fitting of recession-curve (of the Ranichauri spring under study) with two exponential components gives accurate results. The maximum value of exponential coefficient (i.e., 0.0206) represents the major contribution to drainage from the spring-catchment’s portion with highest permeability, whereas the minimum value (i.e., 0.0016) represents the major contribution to spring discharge from the portion with lowest permeability. Analyses show that the permeability of the porous medium is responsible for discharge rate and its capacity is responsible for perennial or seasonal behaviour of the spring. Using the mean values of the recession parameters, the master discharge-function of the spring for the recession period is formulated for calculating its discharge-rate during the recession period of any year. Apart from the year 2001, its predictions are in close agreement with the actually monitored data. The efficiency of the formulated master discharge function of the spring for the recession period has been evaluated equal to 0.965 using the Nash–Sutcliffe efficiency criterion.