eChapters

9.1. Introduction

Human dependence on natural processes for the goods and services provided by nature, especially food, fuel and fibre, has been a known fact. In recent times, the value of less tangible services, such as climate control, water f iltration, and soil fertility, as well as recreational and cultural services has been emphasized also. Ecosystem services underpin human existence, health, and prosperity. It has been beneficial to humans through the transformations of resources (or environmental assets, including land, water, vegetation, and the atmosphere) into a flow of essential goods and services like clean air, water, and food (Costanza et al., 1997). Ecosystem services are those functions of ecosystems- including agroecosystems that are useful to humans or supportive of human well-being (Kremen, 2005). Services provided by ecosystems receive little notice for their support to human civilization often leading to poor management of the ecosystems. Land use systems influence ecosystem functions, which determine the supply of ecosystem services. Land and water resources are under considerable pressure from the expansion of cultivated and residential lands. Diverse land use in agrarian landscapes not only fosters biodiversity, but also provides potential ecosystem services such as air cleaning by vegetation, natural water filtration by plant roots, natural pest suppression, soil conservation, nutrient retention, and crop pollination by insects, etc. Lowland floodplains or waterlogged land areas are generally more conscious of the benefits provided by ecosystem services. It is important to create awareness among the people on provisioning services provided by ecosystems, such as crops, biofuel, fresh water, natural medicine, wildlife, and several cultural services. Managing ecosystem services, which link human well-being to conservation outcomes, is essential for achieving the sustainable development goals (SDGs) of the United Nations (Zhang, 2017).

10.1. Introduction

Irrigation facilities are created by the Government at huge cost for supplying water to the farmers for raising crops to increase agricultural production. The major and medium irrigation projects are planned, constructed, managed, operated and maintained by the Irrigation Departments, wherein certain procedures and rules are evolved and followed to the delivery schedule of canals, frequency of supply and distribution of water to the farmers, and closing of canals. The creation of such facilities resulted in ushering the green revolution in the sixties and seventies in the production of food grains and also employment generation in the country, thereby improving the socio-economic condition of Indian farmers. However, optimized management of irrigation water is the key to the sustainable development of agriculture and livestock. Since management of water for irrigation is highly location-specific, depending upon agro-ecological and socio-economic conditions, type of irrigation project and land use pattern, it differs from project to project and region to region in the country.

1.0 General

 The design of canal involves following three major aspects:

 A Irrigation and drainage canal network planning.

 B Determination of discharge / capacities of  canals and drainages.

 C Determination of shape and size i.e. geometrical dimensions of the proposed canal section, generally

 known as design of canal section. More appropriately it can be called as design of internal section

 of canal. It can be further divided in three following parts viz.

 i. Design of unlined canals:

 ii. Design of lined canals: or a canal may be partly lined and partly unlined.

 iii. Choice between the unlined and lined canals. This aspect should be distinguished from the selection of type of lining. However, the scope of choice of lining may include both the aspects.

 The design of canal section remains incomplete without the design of its embankments, either in lined or unlined canal, so the next aspect is

 iv. Design of canal embankments. Still to complete the design of a canal one more aspect is required i.e.

 v. Canal aesthetics and canal arboriculture.

Theoritical aspects of design has been discussed in chapter 1. Discharging capacity of canal is

 computed by Manning Equation (1)and continuity Equation (2) (Para 1.4).

 In the Manning's equation  V  =   R2/3  S1/2 / N (Eq. 1, Para 1.4);  N and R play most important role.

 The effect of  R has been discussed in para 1.4.1, Chapter 1. In this chapter the complexities of Manning's n (or N, also known as Manning's rougosity coefficient

 or simply rougosity coefficient) and some practical aspects of composite sections and velocity in best

 Mehboob, trapezoidal or rectangular sectioned channels are discussed.

2.0 Manning's Rugosity Coefficient (n)

Value of N depends upon a number of factors such as , surface roughness, vegetation, obstructions, type of lining, age of lining, erosion and damages in lining, curves, discharging capacity , perimeters, depth of flow, velocity etc. These are discussed below and commonly adopted values of n are given in tables 2.1 to 2.3.

A canal of approximate discharge of less than 80 cumecs (3000 cusecs) discharge may be called a medium or low capacity canal).

3.1 Mehboob Section

A Mehboob Section is only a modification of best trapezoidal section by making its complete bottom circular as shown in figure 3.1. Also see figure 1.6 and para 1.7. That is why these canals are also known as canals of zero bed width, or trapezoidal canals with curved bottom, or cup shaped canals.

But these cannot be called as triangular canals with curves, as often spoken. In fact it is a truncated triangle circumscribing the semi circle. Trapezium is also a truncated triangle circum scribing a circle.

More accurately it can be said as a combination of semi circular and best trapezoidal section so as to take full advantage of their hydraulic efficiency and practicability.

This is such a beautiful section that the designer can never commit a mistake, even if he wants to commit a mistake. The dimensions are so geometrically fixed that no one can play with any dimension.

The value of this section was realised for the first time by Er S I Mehboob (1943) in his Punjab Irrigation Branch Paper No.260" Lining of Canals". There after this canal section became well known as Mehboob Section after his name. He also stated that the most economical section i.e. the maximum area for the minimum perimeter is when the centre of the arc is at the full supply line of the section. This is also evident in figure 1.6. This is also the condition for all best hydraulic sections. This section is also useful to a higher silt carrying capacity than a wide shallow one..

A canal of more than 80 cumecs (3000 cusecs) approximetly may be called as a high capacity canal.

It has already been pointed out in chapter 1, that for the best section of any shape, R is always equal to d/2 only, and such depth is the most optimum depth. But such channels are not always practical or most economical due to many other practical reasons, (see para 4.1 and 6.3) and many times shallower depth then this depth is adopted. Typical examples are lining of existing earthen channels, given in para 6.3.

All the best sections have fixed ratio of dimensions very near to the semi circle. For large discharges, radius of semi circle increases that, means depth of canal as well as velocity increases. But higher velocity is not permissible with every type of lining (see table 2.1 and para 2.3). Similarly depth also has limitation of construction, maintenance, stability of slopes, etc. see example–4.2.

Because of limiting velocities and depth, deeper canal section are not practically feasible/possible. Therefore for large discharges, say more than 100 cumecs, Mehboob or best trapizodal sections are just not possible/practical, and recourse has to be taken to trapezoidal section with increased bed width then depth. This section is hydraulically inefficient or uneconomical. Larger the B/D ratio, larger is the inefficiency and section is more costly. (For Mehboob Section, B:D ratio is zero and for best trapizodal section it is much less than 1, see para 3.1, table 3.1 para 3.5 and table 3.4).

A. Rectangular Canals

5.1 Design of Best Rectangular Canals

After the Mehboob and Trapezoidal canals, next best section is rectangle. This section is also generally adopted for small discharges say upto 10 cumecs (350 cusecs). This section ranks at No. 4. Yet, this is the only section most commonly adopted for flumes of discharges upto140 cumecs (5000 cusecs). Typical example is Orsang acqueduct, 1 km. long for 1140 cumecs (40000 cusecs) in ractangular sections on Narmada Canal Project, Gujrat, India, built in the years from 1990 – 2000. Such sections are common in power house canals due to limitation of space and very sharp curves. It is free from the effect of change of side slopes as in the trapezoidal canals (see para 3.3) Still some small side slope (batter) is adopted in thick masonry / concrete lining. It adds to structural stability with economy in thickness of wall and as well as hydraulic efficiency. It may still be called as rectangular section.

Details of its hydraulic efficiency in comparison to semi circle, Mehboob and trapeziodal sections are discussed in chapter 1, para 1.8

6.0 General

No lessons can be drawn without the experiences of the past. In fact, much of engineering, rather all sciences have developed in bits and pieces from the experiences of the past. The engineers by and large have never become wiser in one day. They have become wiser slowly and slowly with their own experiences and from the experiences of past engineering works. Wisdom lies to gain wisdom from experiences/draw lessons from the marvellous engineering works constructed so far. It helps us in a direction for further development of technological skills.

Here an effort is made to draw lessons from experiences of the canals constructed in the past.

 There are several aspects of such experiences. A few important aspects of studies are:

 (i) Internal hydraulic sections of the canal with respect to discharge, topography, stability of side slopes, type of lining, operation and maintenance problems and their solutions etc.

 (ii) Design of canals banks (embankment) with respect to discharge, depth of flow, depth of cutting /filling, below/above natural ground level, type of soil, topography, operation and maintenance, drainage of banks etc.

 (iii) Canals aesthetics and arboriculture

 (iv) Other utility/service of canal such as multi-objectives of hydropower, irrigation, drinking/industrial water supply, social needs of recreation, forests etc.

A brief description of IGMC is given in Para 6.6 with details of the canal sections. Here an attempt is made to review the hydraulic performance of the Main Canal.

7B.1 Study of Flow Characteristic of the Main Canal

The main canal is designed for a maximum discharge of 524 m3/s at head i.e. at Km. 0. Large of number of branches, distributaries and minors off take from the main canal at different location all along the canal. These are shown in the L- section, Figure 7B.1 and a statement off taking canals is given Table 7B.1. Many distributaries such as lift canals have been planned subsequently. Also discharges of few off taking channels have been changed. A clear and updated data are not readily available. So data available are indicated in the Table and plotted in the L - section. A half bottom plan of the canal is also shown in Figure 7B.2

8.1 Design of Canal Embankments

 There are two aspects of canal embankment design.

 (i) The general requirement, such as free board, dowel, service/inspection road, drainage of banks etc. The aspect of free board is discussed in Para

8.2 to 8.3 and that of service/ inspection road in Para

 8.4 and drainage of banks in Para 8.5 in this chapter.

 (ii) Safe design of embankment i.e. Hydraulic and structural requirement.

It includes stability of inner and outer slopes, Structural safe design of inner cut slopes in deep cuttings in different types of soils/rocks of varying nature and ground water conditions. Stability of slopes may include drainage, so as to prevent rock falls/debris in canal. For outer slopes in embankment (filling sections) hydraulic gradient/pharetic line, toe drains etc, similar to the earthen dams, on different types of soil/rock foundation with respect to varying ground water level conditions are important.

The canal embankments in filling may even fail through its foundations by sloughing or liquefactions. All these aspects of canal embankments are discussed in this chapter in Para 8.4 to 8.9.

So far much have been talked about the best hydraulic sections, as these appeared to be most economical sections. But as it appears may not be always true and there are exceptions to each individual site conditions.

9.1 Suitable and Economical Cross Section

Best hydraulic sections are most economical in lined and unlined canals. In lined canal this section is economical as long as the cost of earth work (excavation and embankment) is less than the cost of lining per unit length of channel and this is the most usual case. These sections, besides having least area and perimeter also have minimum top width. Therefore land width required is also minimum, in comparison to other wide sections. But if the cost of earth work / excavation is more, such as in rocks, or in very heavy cutting/filling, best hydraulic section do not remain most economical, and recourse to alternative section must be worked out.

Even in unlined channels in deep excavation or in deep filling recourse must be taken to narrower and deeper sections as far as possible.

Also the type of lining in the bed may be cheaper than the lining on sides and in such cases, lining of best section is no more most economical and cost economics of various alternatives including increase in bed width has to be worked out, see para 4.1 and 6.3.

Introduction

An integrated approach to understanding the changing dynamics in water resources involves taking into account various factors that influence the management of water resources under changing climatic conditions (Pahl-Wostl, 2007). It is a holistic approach that combines different disciplines, including hydrology, climatology, ecology, geography, and social sciences, to develop a comprehensive understanding of water resources. The integrated approach is essential for several reasons, including addressing climate change impacts, sustainable management of water resources, enhancing water security, addressing water quality issues, and promoting collaboration among stakeholders. Climate change is causing alterations in precipitation patterns, melting glaciers, and changes in river flows, affecting water availability and quality. An integrated approach helps in understanding the climate change impacts on water resources and developing adaptation strategies (Asif et al., 2023).

Introduction

R language is a popular and versatile tool for hydrological data analysis and visualization, offering several powerful packages for handling and analyzing hydrological parameters such as river flow, precipitation, groundwater levels, and water quality parameters. R language provides a wide range of statistical functions for hydrological parameter analysis, including time-series analysis, frequency analysis, trend analysis, and regression analysis. Moreover, R’s powerful graphics capabilities make it possible to create high-quality and customizable visualizations of hydrological data. In addition to its statistical and graphical capabilities, R also offers a wide range of packages for data manipulation and cleaning, making it a powerful tool for preprocessing hydrological data. R’s ability to handle and analyze large datasets also makes it well-suited for processing and analyzing large hydrological datasets. Furthermore, R has a strong community of developers and users who regularly contribute new packages and tools, providing a constantly evolving stage for hydrological analysis. Overall, R is a versatile and powerful tool for hydrological data analysis and visualization, offering numerous capabilities and resources for informed decision-making in water resources management and related fields.

Introduction

Hydrological data visualization plays a crucial role in analyzing and understanding the behavior and characteristics of water resources. By visualizing hydrological data, we can gain insight into the distribution, variability, and trends of different hydrological variables such as river flow, precipitation, groundwater levels, and water quality parameters. This information can help decision-making in areas such as water resources management, flood forecasting, and climate adaptation.

R Language is a popular and versatile tool for hydrological data visualization, offering several powerful packages for data analysis and visualization. Each of these packages has its own strengths and limitations, which can be leveraged depending on the specific needs of a given analysis. For example, ggplot2 is an extensively used package for creating publication-quality static plots that are customizable and visually appealing. This package is based on the grammar of graphics, which provides a new plotting system that combines the benefits of both base and lattice graphics. ggplot2 can be used to create a wide range of plot types, including time-series plots, spatial maps, and scatterplots. It provides several options for customizing plot elements such as axis labels, legends, and plot themes. On the other hand plotly offers interactive and dynamic plots that can be easily shared and embedded in web applications. With plotly, we can create plots that allow for zooming, panning, and hovering over data points to display additional information. This package is mainly useful for exploring relationships between hydrological variables. In addition to these packages, hydroTSM provides functions for reading, manipulating, and plotting time-series data. hydroTSM can help us create time-series plots of variables such as river f low, precipitation, and temperature, with options for adding trend lines error bars, and annotations.

Introduction

Evapotranspiration is a vital process in the Earth’s water cycle, and it involves two main processes—evaporation and transpiration. Evaporation refers to the conversion of water from its liquid state to its gaseous state, which occurs primarily from the surface of bodies of water, wet vegetation, and soils. This process requires energy, which is typically provided by direct solar radiation and ambient air temperature. Transpiration, on the other hand, is the process by which plants release water vapor through small openings in their leaves called stomata. This process is essential for plant growth and function as it helps regulate the plant’s temperature and allows for nutrient uptake and water transport. Like evaporation, transpiration also requires energy, with factors like vapor pressure gradient and wind speed influencing the rate at which water is released.

To accurately measure evapotranspiration, it is necessary to consider a range of factors such as temperature, radiation, wind speed, and humidity. Plant parameters, such as the presence of a cuticle or the size and number of stomata, can also greatly influence the transpiration rate. Other factors that may impact evapotranspiration include the season, time of day, and soil properties such as water holding capacity and root depth. Evapotranspiration is a complex concept that has been studied by various scientists and organizations over time. Three main evapotranspiration (ET) concepts have been developed: Reference ET, ET under standard conditions, and ET under nonstandard conditions. The goal of determining potential or reference evapotranspiration is to exclude crop-specific variations from the evapotranspiration process. The potential evapotranspiration concept, introduced in the late 1940s and 50s by Penman, assumes constant crop conditions and defines it as “the amount of water transpired in a given time by a short green crop, completely shading the ground, of uniform height and with adequate water status in the soil profile.” ETo, which is a climatic parameter, represents the evaporating power of the atmosphere at a certain location and time of the year and is computed from weather data. It does not take into account crop characteristics or soil conditions, and the only factors affecting it are climatic parameters. The range of ETo varies from 1–2 mm/day in humid and subhumid temperate regions to 6–9 mm/day in warm arid and semi-arid temperate regions and from 2–3 in cool humid and subhumid tropics to 6–8 mm/day in warm arid and semi-arid tropics. Actual ET is the amount of water on a large area of grass that is actively growing and covering the entire soil surface it actually uses. The amount of water that is actually evacuated from a surface as a result of the processes E and T is known as ETa. Crop water needs can be calculated by the following equation.

Introduction

Droughts are considered to be a significant environmental disaster and have captured the attention of various experts, including environmentalists, ecologists, hydrologists, meteorologists, geologists, and agricultural scientists. These natural calamities are known to occur in almost all climatic zones, regardless of whether they are high- or low-rainfall areas. Generally a decrease in the amount of precipitation received over an extended period such as a season or a year, is the primary cause of droughts. However, other factors such as high temperatures, strong winds, low relative humidity, and characteristics of rainfall (e.g., intensity, duration, onset, and termination) also play a crucial role in their occurrence. It’s important to distinguish a drought from aridity, which is a permanent feature of a climate and is limited to low rainfall areas (Wilhite, 1992). A drought is a temporary phenomenon and can last from a few months to several years. Some people often mistake droughts for heat waves, but Chang and Wallace (1987) highlighted the fundamental difference between these two events. A heat wave typically lasts for a week, while a drought can extend for several months or even years. When a heat wave and a drought coincide, it can lead to dire socio-economic consequences.

Introduction

In recent decades, severe weather and climatic occurrences have become more frequent, affecting human populations across the globe. These changes are caused, in part, by anthropogenic climate change. Vulnerable communities are particularly affected by these rapidly changing patterns, which can have catastrophic consequences. To mitigate the impact of climate change, communities must have access to accurate and up-to-date climate information. Weather predictions, from short-term forecasts to long-term scenarios based on data from previous decades and centuries, can provide valuable information to socioeconomic sectors that are vulnerable to climate change. Climate services offer scientifically-based data and forecasts that can assist decision-makers in managing the risks of climate variability and change. Globally accepted indices generated from daily temperature and precipitation data can indicate the more severe features of climate change. These indices are developed and analyzed by the CCI/WCRP/JCOMM Expert Team on Climate Change Detection and Indices (ETCCDI) and have made a significant contribution to the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports.

Introduction

The hydrological cycle transfers water and energy between the land and atmosphere, but its regional characteristics make accurate modeling challenging. Hydrological models aim to predict hydrological events and processes, but there are uncertainties in their output due to the complex nature of the system and assumptions made. Empirical models use statistical or mathematical relationships, while process-based models use equations to represent physical processes.

Hydrological modeling involves various steps, leading to uncertainties that can affect the accuracy of model predictions. The four main types of uncertainties commonly encountered are data, model, parameter, and climate uncertainty. Data uncertainty arises due to errors or gaps in the input data, model uncertainty stems from limitations in the model structure or assumptions used, parameter uncertainty arises due to uncertainties in the values allocated to various model parameters, and climate uncertainty refers to uncertainties in the future climate projections used as inputs.

Introduction

Time Series Analysis (TSA)

TSA is a crucial tool in the study of climate change, as it allows researchers to carefully examine patterns and changes in weather parameters over time. By analyzing time series data for temperature, precipitation, and other weather variables, scientists can identify trends and develop models that accurately describe the underlying structure of the series. These models can then be used to make predictions about future changes in weather patterns and the potential impacts of climate change on the environment and human society. The accurate forecasting of climate change using TSA can inform policy decisions and facilitate adaptation strategies to mitigate the effects of a changing climate.

Components of Time Series

When analyzing a time series, we often want to separate the different components that contribute to its overall behavior. The classical decomposition method is a widely used technique that breaks down a time series into four components: trend, seasonal, cyclical, and irregular.

Introduction

Time series analysis is a powerful tool for detecting and describing sequential processes, and it has become increasingly important in water resource management, especially in the context of global warming and climate change. Statistical methods have been widely used for analyzing climatological time series, such as precipitation, air temperature, and evapotranspiration, and hydrological time series, such as streamflow and surface water quality. However, most of the linear time series models depend on strict assumptions, such as homogeneity, trend-freeness, stationarity, non-periodicity, and lack of persistence, which are often violated in real-world datasets. Therefore, there is a need to develop new models that are more flexible and can accommodate different types of data (Machiwal & Jha, 2006).

One of the most popular and widely used classical time series models is the Autoregressive Integrated Moving Average (ARIMA) model, which has linear statistical properties and can be built using the Box-Jenkins methodology (Box and Jenkins, 1970). This model adoption is important for hydrological analysis because it can help in accurately characterizing and predicting the behavior of hydrological time series data. ARIMA models can capture complex patterns and trends in the data and can be used to forecast future values of the time series. This can help in better understanding the underlying processes that drive hydrological variability, such as changes in precipitation patterns or land use. Furthermore, hydrological data often exhibit seasonality and long-term trends, which can be accounted for in ARIMA modeling. ARIMA models can also be used for anomaly detection, identifying unusual events that may have significant impacts on water resources. Overall, ARIMA modeling provides a f lexible and powerful framework for analyzing and forecasting hydrological time series, which is essential for effective water resource management in the face of changing environmental conditions.