ANALYSIS OF DISCHARGE VARIATION AND ESTIMATION OF RECESSION COEFFICIENTS FOR DIFFERENT SPRING SYSTEMS IN HIMALAYAN TERRAIN

Abstract

Nowadays water scarcity is the biggest threat to global population due to reduction in rainfall, shrinkage of mountain glaciers and pollution of fresh waterbodies by anthropogenic activities. Springs are considered as the sources of fresh waterbodies in mountainous regions. However changes in rainfall pattern, land use/land cover changes occurring in a recharge area and aquifer’s capacity to store groundwater directly reflects on the spring discharge characteristics. Therefore to understand aquifer’s nature of a spring systems we have to (i) estimate recession coefficients of different spring systems (ii) determine effect of evapotranspiration(ET) on water level fluctuations (iii) construct Master Recession Curve for individual recession segments of different spring types and (iv) implementation of rejuvenation work in the recharge area of a springshed. To understand the specific objectives of this study, the detailed discharge hydrograph analysis for three spring systems (contact, depression and contact-and-fracture) from various parts of Uttarakhand has been conducted for three specific periods such as pre-monsoon (Apr- June), monsoon (July-Sept), and post-monsoon (Oct-Dec). Recession flow consists of two types of components such as baseflow and interflow. Baseflow represents in terms of baseflow coefficients (αb) and interflow in terms of interflow coefficients (αi). For contact type spring αi and αb lie in a range of 0.01-0.04(day-1) and 0.05-0.78(day-1) respectively. Estimated MRC shows that recession period for interflow continues for 6 to 9 days and baseflow for 85 days for contact spring. Similarly for the case of depression spring system αi has a range of 0.28- 0.76(day-1) and αb has a range of 0.01-0.03(day-1) but the resulting MRC suggests both interflow and baseflow significantly contribute to spring discharge during recession period. For contact-and-fracture spring system baseflow recedes at a constant rate of 0.01(day-1) all through the year and αi has a range of 0.16-1.02(day-1). For this system, MRC suggests baseflow is the dominant component over interflow. Climatic condition in the form of ET has a major role in the variation of spring discharge (especially shape of the recession hydrograph). During summer period, ET rate is very high (up to 5.63mm/day) results 9 mm decline in water level. To check discharge variations among different spring systems, statistical methods like ANOVA and T-test have been adopted. In recent decade climatic change (erratic rainfall pattern) and human activities (increased ground water pumping and deforestation) have an adverse impact on springshed. So certain engineering and biological measures like construction of trenches, pits are carried out in the recharge area for effective rainwater harvesting and enhance groundwater storage capacity of aquifer system.