HYDROLOGICAL RESPONSE OF AN EXPERIMENTAL WATERSHED OF LESSER HIMALAYA

Abstract

Water availability over the earth surface as 97% in sea and 3% as fresh water, out of which very less amount is available for the utilization of mankind. Further climate change, growing population and poor management poses threat to meet the future water demand. This issue in Himalayan mountainous region on which 40% of the world’s population depends face more challenges due to remoteness, susceptibility to natural disaster and restricted access for agriculture. Much of the water from the surface and sub-surface in mountains which keep the environment thriving and sustains increasing population have become under pressure. Water scarcity and other quality issues is consequences from unmanaged use and lack of hydro-meteorological data. Water quantification is of major concern in the India sub-continent especially in mountain region which required to cope up the issues of hydro-meteorological gauging locations and understanding of surface and sub-surface flow to meet the needs of water for domestic need and socio-economic development. The continuous monitoring of hydro-meteorological gauging data can support unfavorable influences of extreme conditions. Thus, an experimental watershed through intensive field instrumentation in Aglar watershed which comprised of different sub- watershed (Aglar, Paligaad, Balganga) located in Uttarakhand which has gained little attention in research is developed. After the instrumentation, rating curves have been developed using power law at all the three sub watershed by means of installing water level recorder for stage and salt dilution for discharge measurement. Considering error as inherent, an attempt has taken to quantify uncertainty in rating curve which is not in practice using maximum likelihood method. The uncertainty estimated was 11.9%, 28% and 43% in Aglar, Balganga and Paligaad sub- watershed. Weighing factor concept has been introduced which correlate the degree of uncertainty with morphology of watershed. Detailed analysis of observed rainfall and surface flow were made to understand the hydrological responses of Aglar and Paligaad sub-watershed. Rainfall-runoff analysis revealed that in Paligaad, the rising and falling limb of the hydrograph are steeper with shorter time lag and respond to all rainfall events. But in Upper Aglar sub-watershed, during dry period it not respond to all the rainfall events, and flow only increases when there is enough antecedent soil moisture present. The quick response at Paligaad is because of the limited capacity to reserve the ii water as compared to Upper Aglar. The flow duration curve of a Paligaad tends to have higher “high flows”, than Aglar representing more frequent extreme conditions and slope of the lower end for both watershed shows the characteristics of the perennial storage. Other than the surface flow, the subsurface flow (spring) is the main source of domestic water and there is growing concern about the drying of spring or becoming seasonal. Thus a fracture-and contact-type spring located in the same watershed has been instrumented to understand dynamic nature and model the recession behaviour of spring to gain information during lean period. Analysis of 10 rainfall and spring discharge events shows that, combined power law and exponential relationship fits the recession curve during the dry period whereas least square method fits recession curve during wet period. Relationship between (–dQ/dt) and (Q) for different recession events, characterizes the dynamic behavior of spring. Quantified spring volume force to develop water resource system for agriculture by evaluating the crop water requirement and possible better strategies to improve the water productivity of the region. The total water requirement for all their major crops is 6411.35mm and spring has potential to supplement the water requirement. Adopting the SRI practice, increases water productivity and sensitivity analysis of benefit to cost recommends that increase of crop yield by 30%, increase the revenue by 217%. It is thus essential to optimize the available water and area for irrigation for sustainable management of water resource development. To further increase the spring water, the springshed intervention practices were implemented to increase spring’s discharge. The measured average flow was 16.09lpm but soon after the intervention work the average flow increased by 2.6 times. Post-intervention work (2017) has increased the decay durations to 116 days for 142.98lpm (peak flow) to 12.69lpm (base flow) as compared to previous 100 days to recess from 30.3lpm to 3.93lpm in year 2014 and 98 days to recess from 80.07lpm to 16.4lpm in year 2016. The characteristic value from flow duration curve for the study location is increased to 95lpm after intervention from 30.6lpm. The above findings from the surface and subsurface can be considered as check for establishing benchmarks for sustainable development of watershed, climate change adaptation and development plans to cope up the water insecurity in rural Himalayas. Ability of the sub-surface flow for supplement agriculture water will help for better planning strategies which are resilient to face future challenges as well as advance the economic conditions of Himalayan rural farmers.