In the hills of Uttaranchal,
small streams (gadheras) normally flowing at a steep gradient are used as
source of water for gravity water supply schemes. Boulder Filled Gallery (BFG)
is the conventional water source tapping arrangement. During monsoons
considerable flow and high velocity of flowing water causes heavy thrust on
cross wall endangering the safety of structure. In case of structure surviving
the flow, the problem of silting in the ponding area on upstream side causes
choking of perforated pipes and intake chamber. Further, the high velocity of
water results in erosion of down stream pitching and foundation, making the
foundation exposed and ultimately
leading to the settlement of foundation and failure of structure.
To address this persistent problem in BFG maintenance, an
innovative technology namely the Uttaranchal Well has been applied in Swajal
based on Uttaranchal Jal Sansthan experiences. Uttaranchal well is a device to
tap the sub-surface flow of gadhera, which has a direct connection with the
surface flow of water. The sub-surface flow of a perennial stream under
hydraulic pressure is tapped in this system.
The sub surface flow of the stream rises in the cylindrical
pipe through its open end and perforated radial pipes due to hydraulic pressure
of the submerged surface and maintains a static level in the cylindrical pipe.
The outlet pipe, which is placed at the middle of the well, is connected to the
gravity main of the water supply scheme. The gravity main starts drawing water
from the well. The static
level of the well is maintained due to hydraulic pressure. Thus a continuous
flow is maintained. The scheme is designed considering the minimum discharge of
the stream during the summer.
Uttaranchal Well has been
installed successfully in three villages Sara, Shera Sonali and Kamtoli of
district Pithoragarh. The Uttaranchal well system in above villages is working
satisfactorily for past one year.
The advantages of Uttaranchal
Well over BFG are
1- Construction: The construction of Uttaranchal Well is
easier and speedy. The capital cost is about 14% of the cost of BFG.
2- Filtration: The sub-surface flow is tapped after
natural process of filtration and with upward flow, thereby removing the
turbidity and suspended particles to a great extent.
3- Easy Maintenance: The absence of Slow Sand Filter (SSF)
reduces the quantum of maintenance works to a great level. The provision of
gravel, grit and sand envelope around Uttaranchal Well and its strainer
minimizes the chance of choking the structure.
4- Low risk of damage: As the whole structure is below the
bed level of gadhera, the chance of damage due to big boulders or high velocity
surface water flow hitherto prominent in the case of BFGs, is negligible.
The successful installation and subsequent maintenance
of Uttaranchal Well in these three villages has demonstrated that this
innovative technology can be implemented as source work for gadhera schemes.
However, a detailed assessment of the efficacy of these wells as well as those
executed by other departments needs to be done before replicating it on a wider
scale.
J.R. Sharma
Ex. Engineering Consultant,
DPMU, Pithoragarh
No comments:
Post a Comment