6 GEOGRAPHY AND TOURISM, Vol. 6, No. 1 (2018), 41-53, Semi-Annual Journal eISSN 2449-9706, ISSN 2353-4524, DOI: 10.5281/zenodo.1314016 © Copyright by Kazimierz Wielki University Press, 2017. All Rights Reserved. http://geography.and.tourism.ukw.edu.pl A.S. Zavadsky1, D.V. Botavin, P.P. Golovlev, N.M. Mikhailova, E.A. Morozova, E.V. Promakhova, L.A. Turykin M.V. Lomonosov Moscow State University, Maccaveev Research Laboratory of Soils Erosion and Channel Processes 1 email: [email protected] Results of hydrological studies and channel analysis of the Ganges (Padma) River at the construction site of the “Rooppur” NPP Abstract: This work presents the results of research on channel processes in the Padma River (Republic of Bangladesh) at the construction site of the “Ruppur” Nuclear Power Plant (NPP). The fluvial characteristics of the Padma River were presented, including: the water outflow regime, characteristics of anthropogenic impact on the river outflow and assess- ment of the present state of the channel and floodplain. The research was conducted based on field expeditions, during which data on morphology, dynamics, hydrological and hydraulic conditions for the formation of the floodplain-channel complex were collected. Moreover, the water discharges and suspended sediments, as well as the longitudinal profiles of the water level and the channel morphology were measured. The presented research has shown that comprehensive and planned regulation of selected sections of rivers could lead to the channel stabilization and support the rational use of water resources for different purposes, e.g. power plants, municipal purposes, etc. Moreover, detailed research on channel deformation in selected areas indicated the major role of natural factors (geological structure, the type of sediments deliv- ered to the river, vegetation cover, etc.) in the past and present fluvial processes. Keywords: Nuclear Power Plant “Ruppur”, Ganges (Padma) River, channel processes, bottom and suspended sediment, anthropogenic impact, channel deformations 1. Introduction In April 2015, a team of specialists from the delta system in the world, which is formed by N. I. Makkaveev Research Laboratory for Soils the Ganges, the Brahmaputra and the Meghna Erosion and Riverbed Evolution completed rivers flowing into the Bay of Bengal (Fig. 1). The complex hydrological and riverine studies on drainage system of the Ganges River in the delta a 50-km stretch of the Ganges River in the Peo- area has a complex structure and a hydrological ple’s Republic of Bangladesh. The research was behaviour, determined by the mutual influence related to the beginning of the “Rooppur” NPP of the river and the sea. The average annual project, implemented with the participation of water discharge of the Ganges at the head of the the “Rosatom” Russian corporation. The main delta (Farakka town) is 12,300 m3·s-1 (388 km3/ NPP facilities are located on the left bank of the year). This value corresponds to the specific main channel of the Ganges River (locally called runoff of 13.6 l·s-1·km-2; the runoff depth is 429 the Padma River), 80 km upstream of its conflu- mm; the runoff coefficient is 0.36. The Ganges, ence with the Brahmaputra. At this point, the the Brahmaputra and the Meghna rivers bring river is crossed by the Lalon-Shah Bridge, built together on average 1,230 km3 of water per year in 2001 and connecting the districts of Pabna to the delta. These three rivers account for 31.5, and Kushtia. The Hardinge Bridge railway runs 55.4 and 13.1% of the total runoff, respectively. 300 m upstream of the Lalon-Shah Bridge. Given the lateral inflow to the delta, their total The natural conditions of the study area runoff into the Bay of Bengal is 1,460 km3/year are determined by its location in the largest (Reki i ozera mira, 2012). 42 A.S. Zavadsky, D.V. Botavin, P.P. Golovlev, N.M. Mikhailova, E.A. Morozova, E.V. Promakhova, L.A. Turykin Figure 1. The scheme of river basins in the territory of the People’s Republic of Bangladesh (A) and the study area (B): 1 – the Ganges (Padma); 2 – the Brahmaputra (Jamuna); 3 – the Meghna; 4 – the rivers of the east coast (Karnaphuli and etc.) The main channel in the delta of the Ganges lasts 4 months on the Ganges (from June – the Padma is represented by a braided and to October). This season accounts for over sinuous channel, 1.5-3.0 km wide with a lot 80% of the annual outflow. The most wet of sandbars. A large number of distributaries month is August. The dry season lasts from branch off from the main channel. At present, November to June. The minimum discharges most of them have silted sources and are inad- in the Ganges delta are less than 1,000 m3·s-1 equately recharged. The distributaries split and the maximum in the cross section of the flow separately, then they connect, and then NPP construction site ranges from 70,000 to they split again. At the same time, they have 75,000 m3·s-1. The maximum discharges of different names in different sections. The larg- the Ganges and the Brahmaputra do not usu- est distributaries of this system are the Bhagi- ally coincide in time, but when they do, cata- rathi-Hooghly, the Bhairab and the Gorai. The strophic floods occur in the delta. The maxi- Gorai, with its sources located 17 km below the mum discharges occurred simultaneously in “Rooppur” NPP construction site, is the largest 1962 and were equal to 60,600 m3·s-1 on the one, have the largest discharges and plays an Ganges and 68,200 m3·s-1 on the Brahmapu- important role in watering the western part of tra; the total discharges were about 130,000 the Republic of Bangladesh. m3·s-1 (Reki i ozera mira, 2012). Three cata- The seasonal changes in the Ganges water strophic floods were recorded over the past runoff in the lower reaches are reflected in 30 years – in 1987, 1988 and 1998, when two seasons – wet and dry. The wet season about 37%, 63% and 72% (respectively) of the is caused by the south-western monsoon territory of the People’s Republic of Bangla- and represents a summer flood period that desh was flooded (Mirza et al., 2001). Results of hydrological studies and channel analysis of the Ganges (Padma) River … 43 2. Sediment grain-size composition, methods and results of field studies Field studies were carried out during the period A digital elevation model (DEM) was pre- from 13 April to 28 April 2015. The obtained pared based on geodesic measurements and used results provided information on morpholo- for correction of existing topographic maps. gical, hydraulic and dynamic characteristics Moreover, altitude measurements along 68 mor- of the Ganges river channel (its main distribu- phological cross sections, with a total length of tary – the Padma) under conditions of the low about 200 km were carried out, 740 elevation water phase of the water regime. During the marks in the floodplain, dams, road embank- floodplain survey, the river bank mapping was ments, and eroded banks were measured. carried out according to the degree of manifes- Measurements of the water surface were car- tation of accumulative and erosion processes, ried out on 22 April 2015 at a relatively stable the most common types of floodplain vegeta- water level. The average slope of the water surface tion and the human-induced transformation within the whole area was 0.03‰, which is typi- of floodplain landscapes were analysed, the cal for the areas near the mouth of large rivers in features affecting the water flow in the channel the low-flow period. Along the river, slopes gen- and floodplain were identified. erally increased in the narrowing channels (up The scope of engineering and geodetic work to 0.06‰) and decreased at their extensions (up included: horizontal and vertical measurements to 0.015‰). The hydrographic survey consisted of the terrain surface, association with the state of continuous measurements of the channel geodetic network, levelling (measurements) depths. The result was a 1:10,000 map of channel of longitudinal and transverse morphological relief. Hydrometric measurements of discharges cross sections, and measurements of the water were carried out on 8 cross sections. As a refe- surface slope. In the Republic of Bangladesh, rence, the cross section near the existing river a rectangular BUTM-2010 coordinate system, gauge (between the Hardinge Bridge and Lalon created by the Bangladesh Inspectorate (SOB) Shah Bridge passages) was made. as a derivative of the UTM projection, is used Sampling of bottom sediments was carried in land surveying and mapping. As an altitude out to analyse their grain-size composition and geodetic base, the MSL (Mean Sea Level) alti- their spatial distribution. A total of 254 samples tude measuring system is used, developed by of bottom sediments were collected. They were the Tidal Observatory in Chittagong, where analysed in laboratory conditions; the type of continuous data collection has been carried out sediment was determined according to the ratio since 1993. of fractions and the mean diameter (Tab. 1). Table 1. Particle-size distribution of bottom sediments (% of the riverbed area with low water level) Sub-area Total Sediment type the main channel the old channel (Natore the lower part area from Cape Raita to bend) and the bridge’s of the area Cape Damukdia intersection Silty sand and silts 19% 86% 31% 39% Very fine-grained sand 6% 8% 12% 10% Very fine-grained and fine-grained 10% 5% 11% 9% sand Fine-grained sand 5% --- 22% 14% Fine-medium grained sand 44% 1% 24% 24% Medium-grained sand 16% --- --- 4% Average diameter of deposits, mm 0.21 0.08 0.15 0.16 44 A.S.