27-09-2014, 12:12 PM
CHANGES IN CHANNEL PATTERN OF RIVER GANGA BETWEEN MUSTAFABAD AND
RAJMAHAL, GANGETIC PLAINS SINCE 18TH CENTURY PROJECT REPORT
CHANGES IN CHANNEL.pdf (Size: 588.89 KB / Downloads: 29)
ABSATRACT
Morphological analyses require quantitative description of river course by providing its equation. Such
an equation is not possible as the river plan-form contains loops that cannot be described by it. To
circumvent this difficulty a system of parametric equations is devised for describing the river plan-form.
The system of equations was used to obtain morphological attributes like sinuosity and curvature. Using
the plan-form data for the River Ganga for years 1780, 1828, 1853, 1935 and 1978 the parametric
equations were setup for these years. The plan-forms were to study the changes in channel pattern,
sinuosities and mode of movement of meander loops with time in the last two centuries and in the
downstream direction in the Ganga River between Mustafabad and Rajmahal over about 900 km long
INTRODUCTION
The fertile Ganga plains are heavily populated with about 1/3 population of India residing in these
plains. Any change in its course in space and time affects the life of large population. An understanding
of process controlling its course and changes in it will be helpful to minimize the effects of such changes.
Therefore, the present study attempts to investigate changes in course of the River Ganga between
Mustafabad and Rajmahal (Fig. 1) in the last two centuries.
PLAN-FORM REPRESENTATION OF RIVER GANGA
The tributaries, which bring a lot of discharge and sediment, play a major role in determining the
morphology of the River Ganga. Thus, for better understanding the river plan-form was divided into the
following five patches separated by river confluences:
Reach A: From Mustafabad to Allahabad, where the River Yamuna joins;
Reach B: From Allahabad to Saidpur, where the River Gomati joins;
Reach C: From Saidpur to Maner, where the River Ghaghara and Sone enter the Ganga;
Reach D: From Maner to Monghyr, where the River Burhi Gandak joins; and
Reach E: From Monghyr to Rajmahal.
Acquisition of Data
The river courses for 1780, 1828 and 1853 were obtained from the historical maps acquired from the
National Archives of India, New Delhi. In these maps the river course for 1780 was obtained from the
map F 54/17 published by Rennel on June 22, 1780 on a scale one inch to five miles. The river course for
1828 was obtained by combining the course of the river from map F 166/30 in six sheets (A, B, C, D, I
and J) surveyed by Major R.H. Colebrook in 1801 and Captain Thod Princep in 1828. These maps were
on the scale of one inch to two miles. The river course for 1853 was obtained from sheet No. 88/1, 2, 3
and 103/1, 2, 3, which were published by John Walker, geographer to East India Company, under a
directive of the act of British Parliament. It may be mentioned that the maps of the region Allahabad to
Patna for 1780 and that for the reach from Patna to Rajmahal for 1828 were not available.
The river course for 1935 was obtained from topographic sheets No. 63-G, O, K, which were at
1:253,440 scale published in 1951. The recent course of the River Ganga was obtained from the
LANDSAT imageries taken during different dates of 1970’s by NASA ERTS.
TEMPORAL VARIATION OF PLAN-FORM
Since the river course changes from time to time, the plan-form constants also vary with time. The
plan-form constants have been evaluated for the 1780, 1828, 1853 and 1935. Figs. 4(a)-(b) show the
variation of the end points (x0, y0) and (xN, yN) with time. It can be seen that an end point moves
arbitrarily around its mean position drawing a curve similar to Lissajous figures. In fact all the points of
the river geometry trace figures similar to Lissajous figures. Unfortunately sufficiently long time records
MORPHOMETRIC ANALYSIS
In the first stage of analysis, individual meander loops were identified and were numbered. Examining
and coding the direction and type of changes in each meander elucidated the sequence of movements. The
migrational behavior between two particular dates of each meander was qualitatively determined as
suggested by Ferugson (1976) and was classified as- no change, shortening, extension, rotation and
translation, or complex change. For morphometric analysis, various meander elements like path length,
CAUSATIVE FACTORS
Fig. 11 depicts depict discharge-slope data as given by Leopold and Wloman (1957), and Balek and
Kolar (1959) for the River Ganga at Allahabad, Saidpur, Patna and Rajmahal. Depending on the nature of
the river at the measuring site, the data are demarked as straight, meandering and braided. A perusal of
Fig. 11 indicates that the data of Allahabad and Saidpur fall well inside the field of meandering pattern,
whereas the plot for Patna falls very close to the discriminating line between the two fields and the plot
for Rajmahal falls well inside the braided pattern. Thus, it seems that heavy input of discharge and
sediments from tributaries change the channel pattern of the River Ganga from meandering to braided
downstream of Maner. The River Ganga shows changes in channel pattern in a systematic manner, as
controlled by discharge and slope and sediment load as input from tributaries