Human Interference on River Health

River health is a new branch of geomorphology and hydrology. This chapter mainly deals with the definition of the term, past works as well as the problem related to the present work. River health may be defined as the condition of the anatomy and physiology of any river. Anatomy of any river mainly includes the physical condition of the river, whereas the physiology of any river includes the chemical and biological condition of the river. Physical condition of the river further includes the changing hydrological behaviour of the river, channel shifting and migration, river course change, flood and river bank erosion and related phenomena. On the other hand, physiological condition of the river includes the chemical and biological properties of the river water.

The Haora River basin is located in tropical monsoon climate that indicates hot and moist condition in summer and cold in winter seasons only. During summer, the temperature ranges between 25 and 29 °C, while during winter, the temperature reaches to 18–23 °C. The average annual rainfall of the study area is about 2500 mm, and that is mostly concentrated in the monsoon and late monsoon periods from June to September. The soil in the Haora River basin can be grouped into three distinct categories. These are (a) forest and hilly lateritic soil, (b) alluvial soil (younger and older) and (c) red loamy soil. The entire basin has a gentle slope except the eastern and southeastern part of the basin that is occupied by the Baramura range and other denudational hillocks. Geologically the basin possesses consolidated tertiary (Miocene-Bokabil and Bhuban Formations) sandstone and shale to unconsolidated quaternary sediments. Most of the younger sediments are highly fragile and susceptible to erosion. From the cross-sectional study of the river, it is observed that within the survey period, the river is experiencing changes in its physical and social condition.

This chapter deals mainly with the materials and different methods used in the present study in order to establish the facts and figures of river health of the river Haora. 1932, SOI topographical maps (scale 1:63,360), 1956 US Army topographical map (scale 1:250,000) and recent Google image (2005) have been decoded, referenced and digitised using ARC GIS (v 9.3) software to detect the spatio-temporal changes (gradual changes in channel positions in different years) of the river course. For the study of population growth, Indian Census data for the period of 1981–2011 have been used. Location of brick fields has been demarcated with the help of GPS. Soil erosion of the basin has been estimated on the basis of the Revised Universal Soil Loss Equation, and the amount of sediment yield has been estimated by multiplying bank erosivity and bank erodibility. Water samples collected from the field have been tested in the laboratory in order to find the amount of pollutants in the river water. River course change, USLE, sediment yield, bank erosion zonation, water quality.

The location and sociocultural importance are the main accelerators behind the development and growth of any area. The growth of Tripura as well as Agartala City is mainly started after 1950s. Since then, the general trend of population growth is in increasing pattern. But the growth rate is more (>30,000 persons) in the Agartala area and its surroundings (namely, Dukli, Pratapgarh part, Jogendranagar, etc.). The density of population is also high (>1000 persons/km²) in the aforesaid areas. From the analysis of Census data for the year 1981–2011, it is found that the ST population are in decreasing trend. The growth rate of ST population is very low near Agartala and their major concentration has been noticed in the hilly part of the basin. Although the growth of SC population is high in town part, most of them are marginal workers and some of them are engaged in industrial sectors.

The trend of household distribution is showing a great variation within the entire basin. The growth of household in Agartala and Dukli areas always remains high, but households are still very less in the Baramura part of the river basin. The economic status of the Haora River basin is indicating a well-grown economy of the area. Although the number of non-workers was higher (>35 %) in previous years (1981–2001), now it shows a declining trend as high proportion of female population are now working as marginal workers in different sectors. The proportions of main workers (both cultivators and agricultural labours) are higher in Agartala and its surrounding region.

The course of a river is very dynamic in nature. After originating from the western flank of Baramura range, the Haora River is flowing in western direction through the Agartala syncline and finally meets with the Titas River in Bangladesh. From the source to its mouth, for the entire stretch, the Haora River more or less has an unchanged course for a time period of 1932–2005 except in three parts where remarkable changes have been noticed during the aforesaid time. The stretches of the Haora River where the changes have taken place are listed below:

Within these three stretches, the course of the first stretch had changed due to some micro-scale tectonic activity and due to structural control. For this change the Katakhal, one of the major tributary of the Haora River, was getting detached from the main river. The Haora River also had change its confluence point with the Titas River in Bangladesh. In the rest two stretches, course changes are evidenced due to rapid human intervention.

Sadar Subdivision which is located along the Haora River is the most economically developed subdivision of West Tripura. Out of 1921 industrial units of West Tripura, 1239 industries are located within this subdivision. Also in the Haora River basin, excepting the residential areas in Agartala town and other urban areas, there are 48 types of industries within which the total number of industries is 358 (based on field survey data).

These 48 types of industries/manufacturing units of the Haora River basin have been categorised into 8 classes based on the types of materials used and the type of pollutants emitted. These are:Among these eight types of industries, three types are found which are very large in number and they possess great impact on the Haora River. These are brickfields, automobile–chemical–fuel industries and hotel–restaurants.

In the Haora River basin, agricultural practice is an important occupation. In the year 1932, a total of 106.38 km² of land was under agricultural practices among which 4.61 km² of land was under shifting cultivation in forested land. In the year 2005, the area under agricultural practices has been increased to 121.17 km² which can increase the problem of sedimentation and pollution to the Haora River.

Slum population has been increasing in Tripura over the last four decades along with the growth and expansion of Agartala City and other towns. From the field survey, a total of 63 patches of households, occupying a total of 3.69 km² along the Haora River, are found in levee top zone of the Haora River within Indian territory. These have been considered as slum and rural run-down areas. Most of these slums and rural dwellers do not have proper sanitation system. Major portion of the dwellers in those areas use Kachha latrine, which releases excreta directly into the river. It pollutes the river water, supplies extra sediment loads to the river and degrades the overall environment. Several industries and markets have been grown up to fulfil the need and greed of human population of the basin. These industries and marketplaces dump waste materials along the banks of the Haora River. Moreover, nine major city drains of Agartala are directly connected with the river. All of these nuisances are making the Haora River sick due to lack of consciousness among the local people as well as the government. All these slum dwellers use the river water for their daily activities. As a result, majority of the population in the Haora River basin suffer from different kinds of water-borne diseases.

The potential soil loss of the Haora River basin has been calculated by using four physical parameters in Revised Universal Soil Loss Equation (RUSLE) method, i.e. (i) rainfall erosivity, (ii) soil erodibility, (iii) slope length and (iv) slope steepness. The minimum potential loss is found in the plain areas and also along the river course (0–3000 tons.ha⁻¹.year⁻¹). The maximum amount of potential soil loss is found in the steep slope area where the rate is more than 9000 tons.he⁻¹.year⁻¹.

Actual soil loss of the Haora River basin has been estimated by multiplying the land cover–land use and adopted conservational practice map with potential soil loss map. More than 250 km² area of the basin is having very less amount of soil loss (<150 tons.ha⁻¹.year⁻¹). On the other hand, there is only 45 km² area which is experiencing high rate of soil erosion (>1500 tons.ha⁻¹.year⁻¹) and can produce soil maximum of 120,000 tons.year⁻¹.

The rate of sediment yield has been estimated from the sediment delivery ratio (SDR) method. From this method, the maximum amount of sedimentation is found along the river courses (>4500 tons.ha⁻¹.year⁻¹), but in the steep hilly areas the sedimentation rate is approximately zero. The trend of estimated sediment yield is quite matching with the field generated data. From their comparative graph, it is found that the difference is positive in the years 1991, 1993, 2003 and 2007 which are well marked as flood year. In the rest of the years, the difference between observed and estimated sediment seemed to be negative.

Naturally bank erosion is a severe problem to any fluvial system. The Haora River is also experiencing severe bank erosion in several parts of its course. Thus the BEHI model has been selected and applied in 60 spots (both left and right banks) along the Haora River (within its Indian territory) as the standard method for estimating bank erosion. From the estimated data, it is found that among the 60 spots, 8 spots are falling in very high erosion category, 13 spots in high category, 22 spots in moderate category, 11 spots in low category and 6 spots in very low category of erosion rate. Finally this method is compared with field generated erosion data, and it is found that models’ accuracy level is exact in 55 % cases, but the result of this model is acceptable for 76.7 % cases.

In this thesis, a new RS- and GIS-based method has been proposed for preparing bank erosion vulnerability zonation. This zonation can be done by estimating eight parameters, i.e. (i) rainfall erosivity, (ii) lithological factor, (iii) slope of the river bank, (iv) meander index of each curve of the river, (v) river gradient (longitudinal), (vi) soil erodibility factor of the bank, (vii) vegetation cover of the bank and (viii) anthropogenic factor which are present across the river. By superimposing all the six individual parameters (the first two parameters are constant for that particular basin), bank erosion vulnerability zonation map has been prepared for the Haora River basin. This method has been compared with the BEHI–NBS method, and it is found the values of both these methods are matching in the case of 31 spots. But there are only five spots, where the values of both the methods are completely different.

A detailed survey has been carried out in order to assess the pollution status of the Haora River at different critical points and in different time periods (2004–2013). All the 15 parameters of the ten selected water samples are categorised into three heads for analysing the pollution status in details. Among physical components of the water quality, total suspended solid and total dissolved solid are very much fluctuating throughout the entire stretch. There is a gradual increase in the total suspended solid towards the lower catchment of the river. But the temporal fluctuation within the period of 2004–2013 is very high. Trace of all the chemical minerals is high in the lower catchment of the Haora River as major concentration of industries and slum clusters are located within this region. In the case of biological components, dissolved oxygen is decreasing towards the downstream part of the Haora River. Both BOD and COD rates are increasing at the lower catchment. The rate of total coliform is increasing in an alarming rate both spatial and temporal levels. The disposal of huge amount of excreta directly into the river from the slum areas is the main cause behind the high concentration of coliform in water.