Taktsom Chu Watershed, East Sikkim

INTRODUCTION
Given that water is a vital and indispensable resource, it is imperative that we
ensure an adequate supply to satisfy people's diverse needs. However the limited
availability and improper management of water pose a threat, to the security of our
food supply, the well being of individuals and overall progress. The competition for
water is already prevalent in the mid-elevation Himalayan watershed of India, as a
result of rapid population growth and land modification for urban development. In
numerous mountainous areas in India, the inadequacy of water has long been a
persistent issue for villages situated in the mid to higher altitudes, far from the main
streams or springs. Additionally, the rained mid-altitude watersheds of the
Himalayan region are profoundly susceptible to seasonal fluctuations in the water
cycle, which poses a severe threat to the overall environmental security.

During times of drought, the upper springs in these habitations run dry, causing
serious water shortages. Similarly, Sikkim is facing challenges due to reduced
discharge in springs and the disappearance of hilltop lakes. It is evident that water
conservation and management efforts are needed to cater to the various water needs
of the people living in the hills. To address this issue, the Planning Commission and
other funding agencies have implemented the watershed development approach to
properly manage natural resources. However, these projects have mainly focused on
increasing land productivity, neglecting the importance of the services provided by
watershed hydrology. The distribution of rainfall across these areas has also been
overlooked.

Sikkim's topography and geography are truly exceptional, as its location has
resulted in it being one of the rainiest regions in the country with a dense network of
drainage channels. As a result, the state boasts abundant water resources. However,
these resources have not been fully harnessed, utilized, or conserved, leading to a
growing realization of the urgent need for sustainable water management facilities.
With its vast potential for tourism, the state has witnessed a steady rise in tourists,
particularly for spiritual and recreational activities such as trekking.
 Sikkim

Terrain

Sikkim's spectacular terrain boasts impressive elevations ranging from 280 to 8,585
meters, spread across a total area of 7,096 square kilometres.
Climate

The state's diverse topography encompasses both subtropical regions and high
alpine landscapes, with temperatures varying from mild summers in the foothills to
freezing winters in the lofty mountains.

Landforms

Surrounded by the mighty Himalayan range on three sides, Sikkim is home to the
world's third highest peak, Khangchendzonga, situated in the western part of the
state. The majestic Teesta river runs through the heart of Sikkim, flowing north-
south with its powerful currents.
Soil

Composed mainly of gneiss and schist, the hills of Sikkim are characterized by
coarse soil with high concentrations of iron oxide, lacking in both organic and
mineral nutrients.

Geological Map

Features

This enchanting state also boasts numerous mountain passes that connect it to
neighbouring countries such as Bhutan, Tibet, and Nepal.

Drainage Map
STUDY AREA

Taktsom Chu Watershed, East Sikkim

This research was conducted in a diverse Himalayan region, spanning from 932m to
3172m in elevation. The study area encompasses a total of 35.42 sq. km,
representing a mere 0.49% of Sikkim state's entire geographical area, situated
between 270°15' to 270°20' N and 880°37'30" to 880°42'30" E.

Nestled entirely in the rugged highlands, this watershed is the primary drainage
basin for the Taktsom Chu river, which eventually flows into the Ranikhola river
near Jalipool, just 2 kms downstream from Ranipool. Taktsom Chu is a vital
tributary of the Teesta Basin, while Ranikhola merges into the larger Teesta river
approximately 30 kms from Gangtok.

The Taktsom Chu watershed is nestled in the south-eastern region of Sikkim,

located in the expansive East district.
It encapsulates a diverse terrain, encompassing two distinct revenue blocks -
Naitam, Assam-Lingzey - that are home to a population of 4,065 (according to the
2001 Census).

Source of water spring in Assam Lingzey

The Naitam section of the watershed boasts steep slopes, while the Assam Lingzey
section boasts more moderate slopes. The elongated shape of the watershed adds to
its unique character.

METHODOLOGY
The beautiful state of Sikkim lies predominantly in the Teesta River watershed. This
study is the result of thorough field surveys and investigations.
 In Gairigaon, Assam Lingzey, manual rain gauges was set up to accurately
measure and documents the daily rainfall.
 Additionally, the water runoff at the Silt Observation Post in Bala khola, a
tributary of Taktsom Chu, was estimated using the Velocity – Area method.
 To measure the velocity of the stream, a float method was employed.
 Each day, water samples were carefully collected in narrow-mouthed
polyethylene bottles.
 These samples will undergo laboratory analysis, with any sediments being
filtered out using pre-weighted Whatman No. 42 filter paper (diameter 125
mm).
 To determine the sediment load, the oven dry method was utilized.
 Finally, Leica Geosyst was used to complete the image registration process.
 The layout of the maps was thoughtfully crafted using ARC GIS Arc map.
RESULTS
1. Rainfall and Runoff Relationship

Precipitation, whether in the form of rain or snow, is the primary source of water for
all ecosystems on Earth, including the land, water bodies, and atmosphere. The
process of rainfall being converted into runoff is a complex, ever-changing, and
nonlinear process that is influenced by a multitude of physical factors.

Understanding and studying this process is crucial for effectively managing and
utilizing available water resources. Rainfall events create runoff, and their
occurrence and volume are heavily impacted by the intensity, duration, and
distribution of the precipitation, as well as other factors like soil composition,
vegetation, land slope, and catchment size. In mountainous regions, understanding
runoff dynamics is especially important due to the unique characteristics and
challenges of these catchments.

The underlying cause behind this occurrence may be attributed to the limited
retention capacity of high mountain regions. The rainfall data from 2008 to 2012, as
depicted in Figure 2, further supports this finding. Interestingly, the year 2009 stood
out as the driest, with a recorded precipitation of only 2468.9 mm, while the years
2008, 2010, and 2011 received significantly more rainfall with amounts of 3695.11
mm, 3665.9 mm, and 3636.5 mm, respectively.
 Dried spring, Assam-Lingzey

A thorough analysis of the runoff patterns for the entire studied period revealed that
there was a consistent trend in most months, with minor variations. However, the
months from August to October showed a significant increase in runoff across all
years, as shown in Figure 3. These findings were further cemented by the fact that
the stream source was found to be a network of groundwater springs in the upper
reaches of the watershed.

In the year 2009, it was confirmed that the watershed experienced significantly less
rainfall (2468.9 mm) than in previous years when it had exceeded 3600 mm.
Despite this, the watershed was able to maintain a higher runoff than expected.

Broken water supply pipe lines

 2. Relationship between Runoff and Sediment load/yield

By examining the sources of sediment yield in a catchment, we can gain valuable

insight into the level of soil erosion taking place in that area. The amount of surface
erosion and sediment yield greatly differs across a catchment, influenced by factors
such as rainfall patterns and the diversity of the catchment itself.

Interestingly, the majority of sediment that flows into the world's oceans annually
originates from rivers in Asia, with the Himalayan rivers being the leading
contributors.

3. Development of local water availability and demand ratio

A comprehensive analysis was carried out for the watershed, looking at the month-
wise water availability and demands for different sectors including households,
agriculture, and livestock, from the years 2008 to 2011 (see Table 1).

This was done to determine any discrepancies between the available water and the
water demand throughout the year. The results revealed that the months from April
to June showed significantly lower ratios of water availability to demand,
highlighting the need for water conservation measures during this time in the
watershed.

Table 1:

Water Availability and Demand Ratio from 2008 to 2011

 4. Population forecast

The development of the population forecast model for the watershed utilized the
method proposed by Bhatti and Nasi (2010). By analyzing data from previous
census reports, the population growth rate of the watershed was determined and
projected up to the year 2030, taking into account past trends.

The forecast considered four potential social scenarios:

 Low growth rates.

 Medium growth rates.
 High growth rates.
 Constant growth rates.

Additionally, the rising population and urbanization in the watershed were taken
into consideration when assessing the high water demand scenario. Conversely, the
low water demand scenario reflects the possibility of an increase in water
conservation due to a growing awareness of its importance.

 According to our population and water demand forecast model, the Taktsom
Chu watershed is expected to experience significant growth in the coming
years.
 Under a constant growth rate, the population is estimated to reach 5728 by
2020 and 6713 by 2030.
 However, the low growth rate scenario predicts a population of 5449 and
6305 in 2020 and 2030 respectively.
 On the other hand, a high growth rate would lead to a population of 6963 and
8579 in 2020 and 2030 respectively.
 But based on previous data trends, a medium growth rate seems to be the
most realistic approach for further analysis.
 Therefore, for our water demand forecast, we have accepted the medium
growth rate. This means that the population of the watershed is expected to
reach 6475 and 7831 in 2020 and 2030 respectively. These figures are based
on the most likely scenario of a medium growth rate.
CONCLUSION
Water security is essential for enhancing food security, improving people's health
and productivity, and reducing poverty while maintaining environmental
sustainability. To achieve this goal, watersheds must be managed as cohesive units,
using rational water budgeting principles and adaptive strategies. This approach will
enable timely identification of any unforeseen effects in the state of Sikkim.

It is crucial that we fully incorporate and maintain integrated monitoring of both

water and ecosystems within our water management practices. This is essential for
achieving success in water management, and hinges on the involvement of a well-
informed public. The interdependence of water resources and climate means that the
potential impacts of global climate change on both water resources and regional
development cannot be ignored.

It is essential to gather measured data on the spatial and temporal patterns of various
components of local and regional hydrological knowledge in order to effectively
manage and develop water resources in the state of Sikkim. One crucial tool for this
purpose is stream gauging stations, which continuously track water flow in streams
over extended periods of time. Through this data, we are able to gain a deep
understanding of our water resources.

One way to improve our scientific understanding of meteorological and

hydrological parameters in the state would be to expand the network of Automatic
Weather Station (AWS). By doing so, we would have access to valuable
information such as stream gauge records, which can provide estimates of water
availability for drinking, irrigation, and numerous other purposes.

In Sikkim, it is crucial to expand the number of permanent monitoring stations for

rainfall and runoff in various rivers and streams across the state. This is important in
order to gain a comprehensive understanding of their correlations and how climate
change affects hydrological patterns.

Additionally, we must work towards developing scientifically-backed rainfall-

runoff relationships for different watersheds, including those from pre-monsoon,
monsoon, and post-monsoon periods. This will enable us to accurately estimate
water yields and ultimately inform effective agricultural water management
strategies.