one of the use of remote sensing

1. Assessment of reservoir
sedimentation by remote
sensing
Anjani kumari
Reg. no.: CUJ/I/2013/1WEM/018

2. INTRODUCTION
• Regular monitoring and updating of elevation
capacity curve of the reservoir helps in better
water management. With this aim conventional
hydrographic surveys are conducted at regular
intervals to assess the sedimentation rate in a
reservoir and to determine the available capacity
of reservoir but conventional method are tedious
and costly. So REMOTE SENSING TECHNIQUE do
offer a modern answer to the costly conventional
surveys.

3. REMOTE SENSING
• Satellite Remote sensing (SRS) technique has
emerged and established itself as a useful cost
and time effective tool to estimate live storage
capacity loss in reservoirs due to
sedimentation. From the data provided by the
remote sensing satellites it has now been
possible to compute loss of reservoir capacity
due to sedimentation and its distribution.

4. Flow chart (methodology)

5. The methodology adopted for this study
involves pre-processing of satellite data,
identifying the water pixels and computation
of the capacity of the reservoir.
To quantify the volume of sediments deposited
in the reservoir, the basic information that
needs to be extracted from the satellite data is
the water-spread area of the reservoir at
different water elevations.

6. • Initially, a false colour composite (FCC) of the
satellite data was prepared and visualized. The
pixels representing water-spread area of the
reservoir were clearly distinguishable in the
FCC. For processing of satellite data generally
it is necessary to geo-reference the images of
different time periods when using the
temporal satellite data of the same area.

7. Modified Normalized Difference Water Index (NDWI)
Method
The condition used to separate the water pixels from the
other pixels is as follows:
NDWI = (DNG - DNNIR )/(DNG + DNNIR)
“If NDWI is positive and if the DN value of NIR band is less
than the DN value of Red band and the Green band (NIR<
RED< GREEN), only then the pixel must be classified as
Water”.
The NDWI value ranges from −1 to 1 and zero is the
threshold .
If, NDWI > 0, cover type is water and if, NDWI
≤ 0 cover type is non-water.

8. MATHEMATICAL COMPUTATION
The reservoir capacity between two elevations can be
computed by following Prismoidal Formula using water
spread areas at corresponding elevations obtained
above:
ΔV1-2 =Δh (A1+A2+√A1*A2) / 3
Where, ΔV1-2 = Volume between elevation E2 and E1
(E2>E1)
Δh= E2-E1
A1, A2 = Water spread areas at elevation E1 and
E2

9. IRS -1A ,IRS -1B two identical satellite are
launched. These 5wo satellite are capable to
provide us data of all Indian reservoir at 11
days interval.
IRS -1C and IRS -1d has also been launched in
28/01/1996 and 29/09/1997 respectively for
better picture even in cloud areas.