Description
Book SynopsisThe book is designed to serve as a textbook for graduate and undergraduate courses on soil and water conservation engineering for students of agricultural engineering, civil engineering, environmental engineering and related disciplines. The book presents the basics of soil and water erosion, and describes the measures to control erosion, focusing on structures to prevent and control erosion. The chapters dedicated to erosion control structures provide a detailed view of each structural construction, covering the function, design and elements of each type of structure. Some common type of structures covered in the book are terrace, bunds, vegetated waterways, and gully control structures, including spillways. The book also covers wind erosion and control structures to prevent wind erosion. Each chapter includes pedagogical elements such as examples, practice questions, and multiple-choice-type questions to improve understanding and aid in self-study. Besides serving as a textbook university coursework, the book can also serve as a supplementary or primary text for professional development courses for practicing engineers engaged in soil and water conservation or watershed management. The book will also serve as a reference for professionals, environmental consultants, and policy makers engaged in soil and water conservation related fields.
Table of ContentsCHAPTER 1
SOIL AND WATER CONSERVATION
Abstract
Soil and water conservation is essential to tackle the global challenge of soil erosion, which is negatively impacting food productivity, water security and environmental quality. This chapter traces the history of soil erosion and introduces the principles of soil and water conservation. It highlights the challenges involved in adopting appropriate measures for preventing and minimising soil erosion. The chapter also discusses the types of soil erosion and their causes. The impacts of soil erosion are analysed from a global in general and Indian perspective in particular. The current and emerging trends in soil and water conservations research are highlighted.
Contents
1.1 Soil and Water Conservation
1.1.1 Principles of Soil and Water Conservation
1.1.2 Challenges in Soil and Water Conservation
1.2 Soil Erosion
1.3 History of Soil Erosion
1.4 Agents of Soil Erosion
1.5 Types of Soil Erosion
1.5.1 Geological Erosion
1.5.2 Accelerated Erosion
1.5.2.1 Water Erosion
1.5.2.2 Wind Erosion
1.6 Effects of Soil Erosion
1.6.1 Global Perspective
1.6.2 Indian Perspective
1.7 Causes of Erosion
1.7.1 Destruction of Natural Protective Cover
1.7.2 Improper Land Use
1.7.3 Improper Cultivation or Cropping Pattern
1.8 Factors affecting erosion
1.8.1 Climate
1.8.2 Topography
1.8.3 Vegetation
1.8.4 Soil
1.9 Recent Trends in Soil and Water Conservation
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 2
WATER EROSION
Abstract
Water erosion encompasses the detachment of soil particles primarily by raindrops and flowing water and their transport by runoff. Comprehending the mechanics of water erosion is essential to develop measures to control erosion. This chapter describes the principal types of water erosion, viz., raindrop splash erosion, sheet erosion, interrill erosion, rill erosion, gully erosion, tunnel erosion and streambank erosion, and explores the mechanics of each type. The chapter also describes various agronomical and biological measures employed to control water erosion. It also introduces popular engineering erosion control measures like terracing, bunding, vegetated waterways and gully control structures.
Contents
2.1 Water Erosion
2.2 Types of Water Erosion
2.2.1 Raindrop Splash Erosion
2.2.2 Sheet Erosion
2.2.3 Interrill Erosion
2.2.4 Rill Erosion
2.2.5 Gully Erosion
2.2.5.1 Processes of Gully Erosion
2.2.5.2 Stages of Gully development
2.2.5.3 Classification of Gully
2.2.6 Tunnel Erosion
2.2.7 Streambank Erosion
2.3 Mechanics of Water Erosion
2.3.1 Detachment
2.3.2 Transportation
2.3.3 Deposition
2.4 Control of Water Erosion
2.4.1 Strategies
2.4.2 Agronomical and Biological Measures
2.4.2.1 Crop Rotation
2.4.2.2 Conservation Tillage
2.4.2.3 Cover cropping
2.4.2.4 Contour Cropping
2.4.2.5 Strip Cropping
2.4.2.6 Contour Strip Cropping
2.4.2.7 Mulching
2.4.2.8 Agroforestry
2.4.2.9 Alley Cropping
2.4.2.10 Buffer Strips
2.4.3 Engineering Measures
2.4.3.1 Terraces
2.4.3.2 Bunds
2.4.3.3 Vegetative Waterways
2.4.3.4 Gully Control Structures
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 3
SOIL LOSS ESTIMATION
Abstract
The soil loss estimated using soil erosion models is vital in evaluating the existing soil conservation practices and identifying priority areas and appropriate measures to control erosion. This chapter presents various soil erosion modelling and measurement techniques for soil loss assessment. The Universal Soil Loss Equation (USLE), an empirical modelling approach, is introduced along with its factors: rainfall erosivity, soil erodibility, slope length-gradient, land cover and management, and soil conservation practice factor. Also, the Modified USLE (MUSLE), which has a runoff factor in place of the rainfall factor, and the Revised USLE (RUSLE), which includes several process-based concepts, are discussed. The chapter introduces the Water Erosion Prediction Project (WEPP), and the European Soil Erosion Model (EUROSEM), the distributed, physically-based soil erosion models that can simulate soil loss under diverse land uses and hydrologic conditions. Also, the Soil Conservation Service (SCS) curve number method and the rational method used for estimating the runoff volume and peak runoff rate are included. The chapter discusses the soil loss measurements from runoff plots. The different sizes plots are discussed along with commonly used devices, namely the multi-slot divisor and Coshocton wheel.
Contents
3.1 Background
3.2 Modelling Soil Loss
3.2.1 Universal Soil Loss Equation (USLE)
3.2.1.1 Rainfall-Runoff Erosivity Factor (R)
3.2.1.2 Rainfall Erosion Index (EI)
3.2.1.3 Soil Erodibility Factor (K)
3.2.1.4 Slope Length-Gradient Factor (LS)
3.2.1.5 Land Cover and Management Factor (C)
3.2.1.6 Soil Conservation Practice Factor (P)
3.2.2 Modified Universal Soil Loss Equation (MUSLE)
3.2.3 SCS Curve Number Method
3.2.4 Rational Method
3.2.5 Revised Universal Soil Loss Equation (RUSLE)
3.2.6 Water Erosion Prediction Project (WEPP) Model
3.2.7 EUROSEM
3.3 Measuring Soil Loss
3.3.1 Erosion plots
3.3.2 Multi-slot Divisor
3.3.3 Coshocton Wheel
3.3.4 Size of plots
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 4
TERRACE
Abstract
Terraces are the most widely practised soil erosion control measure around the world. The practice consists of earth embankments constructed across the steep slopes to intercept surface runoff and divert it at a non-erosive velocity to a safe outlet or store it to enhance soil infiltration. This chapter presents a broad classification of terraces into two types: the common (or normal) terraces and the bench terraces. The chapter presents the design of common (or normal) terraces in terms of their spacing, grades, length and cross-section. The design of bench terraces includes spacing, bench width, cross-section and length, besides the volume of cut and fill or earthwork and area lost under them. The chapter also contains the terrace system planning, including its location, layout and maintenance. The design procedures are demonstrated through solved examples.
Contents
4.1 Definition
4.2 Functions
4.3 Classification
4.3.1 Common (or normal) Terraces
4.3.1.1 Narrow-base terraces
4.3.1.2 Medium-base terraces
4.3.1.3 Broad-base terraces
4.3.2 Bench Terraces
4.3.2.1 Level or Tabletop
4.3.2.2 Inward-sloping
4.3.2.3 Outward-sloping
4.4 Design of Common (or Normal) Terraces
4.4.1 Terrace Spacing
4.4.2 Terrace Grades
4.4.3 Terrace Length
4.4.4 Terrace Cross-Section
4.5 Design of Bench Terraces
4.5.1 Terrace Spacing
4.5.2 Bench width
4.5.3 Terrace Cross-section
4.5.4 Terrace Length
4.5.5 Net Cultivated Area
4.5.6 Volume of Cut and Fill or Earthwork
4.5.7 Area Lost under Bench Terraces
4.6 Terrace System Planning
4.6.1 Planning Considerations
4.6.2 Soils
4.6.3 Landscape
4.6.4 Tillage equipment
4.6.5 Terrace Outlets
4.7 Terrace Location
4.8 Terrace System Layout
4.9 Terrace Maintenance
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 5
BUNDS
Abstract
Bunds are among the most common mechanical measures of erosion control. These consist of small embankments constructed across the land slope to reduce the slope length, runoff and soil erosion and enhance soil infiltration. This chapter presents a broad classification of bunds. It includes the common design considerations for contour and graded bunds like storm frequency, spacing, side slopes, freeboard and seepage through them. The chapter elaborates the design of contour and graded bunds in terms of their height, cross-section, length, the volume of earthwork and area lost under them. The chapter also contains the planning considerations and construction of bunds. The design procedures are demonstrated through solved examples.
Contents
5.1 Definition
5.2 Functions
5.3 Classification
5.3.1 Contour Bunds
5.3.2 Graded Bunds
5.3.3 Side Bunds
5.3.4 Lateral Bunds
5.3.5 Marginal Bunds
5.3.6 Semi-circular Bunds
5.3.7 Contour Stone Bunds
5.4 Common Design Considerations for Contour and Graded Bunds
5.4.1 Storm Frequency
5.4.2 Bund Spacing
5.4.3 Bund Side Slopes
5.4.4 Freeboard
5.4.5 Seepage through Bund
5.5 Design of Contour Bunds
5.5.1 Height of Contour Bund
5.5.2 Bund Cross-Section
5.5.3 Length of the Bund
5.5.4 Earthwork
5.5.5 Area Lost under the Bund
5.6 Design of Graded Bunds
5.7 Planning Considerations for Bunds
5.8 Construction of Bunds
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 6
VEGETATED WATERWAYS
Abstract
Vegetated waterways are natural or constructed channels having vegetative cover to dispose of runoff safely without causing erosion. These waterways are designed using the ‘permissible velocity approach’ and constructed along the natural slope. This chapter presents the preliminary design considerations for vegetated waterways and elaborates the design processes to decide the size, shape, vegetation, permissible velocity and roughness coefficient. Solved examples are included to demonstrate the design procedure. The chapter also contains the layout, construction and maintenance of the waterways.
Contents
6.1 Vegetated Waterways
6.2 Vegetated Waterway Design
6.2.1 Preliminary Design Considerations
6.2.2 Design Process
6.2.2.1 Size of Waterway
6.2.2.2 Shape of Waterway
6.2.2.3 Vegetation Selection for Waterway
6.2.2.4 Permissible Velocity in Waterway
6.2.2.5 Roughness Coefficient of Waterway
6.2.3 Design Procedure
6.3 Waterway Layout and Construction
6.4 Waterway Maintenance
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 7
GULLY CONTROL STRUCTURES
Abstract
Gully control structures, i.e., the check dams, have been used since the 12th century for soil and water conservation and more frequently over the past 150 years. These are employed in severely eroded gullies that cannot be managed with biological or vegetative erosion control measures. The temporary or permanent structures are constructed across the gully to reduce the channel gradient and stabilise the gully to prevent further erosion. This chapter presents the design principles used in designing temporary gully control structures, i.e., different check dams, preferred in areas where labour is inexpensive, and the appropriate construction materials are readily available. The design includes the number of structures, spacing between structures and a spillway to handle the peak runoff due to a 10-year return period storm. Subsequently, the chapter introduces three established permanent gully control structures, i.e., the drop spillway, drop inlet spillway and chute spillway, preferred in medium to large gullies with significantly high flows that the temporary structures cannot handle. The hydrologic, hydraulic and structural design principles of the permanent structures are introduced. The chapter also includes the prerequisites, viz., the specific energy considerations, critical flow characteristics and hydraulic jump, for designing permanent structures.
Contents
7.1 Background
7.2 Temporary Gully Control Structures
7.2.1 Design of Temporary Gully Control Structures
7.2.2 Number of Temporary Structures
7.2.3 Spacing between Structures
7.2.4 Design of Spillway
7.2.5 Types of Temporary Gully Control Structures
7.2.5.1 Woven-wire Check Dams
7.2.5.2 Brushwood Check Dams
7.2.5.3 Log Check Dams
7.2.5.4 Loose Rock Check Dams
7.2.5.5 Gabion Check Dams
7.3 Permanent Gully Control Structures
7.3.1 Design of Permanent Gully Control Structures
7.3.1.1 Hydrologic Design
7.3.1.2 Hydraulic Design
7.3.1.3 Structural Design
7.3.2 Energy Considerations in Design of Permanent Structures
7.3.2.1 Energy Relationships in Open Channel Flow
7.3.2.2 Characteristics of Critical Flow
7.3.3 Hydraulic Jump
7.3.3.1 Types of Hydraulic Jump
7.3.3.2 Energy Dissipation in Hydraulic Jump
7.3.3.3 Length of Hydraulic Jump
7.3.3.4 Application of Hydraulic Jump for Designing Stilling Basins
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 8
DROP SPILLWAY
Abstract
Drop spillway, one of the most widely used soil conservation structures, is primarily used for controlling and stabilising grades in a gully. The chapter focuses on the hydrologic, hydraulic and structural designs of drop spillways. The hydrologic design approaches for estimating the peak flow rate, i.e., the rational method, empirical or frequency factor method of frequency analysis and the hydrological or hydraulic modelling, are discussed. The hydraulic design of straight and box-inlet drop spillways under free and submerged flow conditions is presented. This chapter also includes the critical depth concept and its application in determining the dimensions of various components of the straight and box-inlet drop spillways. The structural design contains the analysis of the horizontal forces acting against the structure due to the hydrostatic pressure of the water column upstream and the earth pressure caused by the backfill. It also comprises the uplift pressure caused due to water seepage through the saturated foundation material. A detailed procedure to analyse the stability of the structure against overturning, sliding, piping, tension, and compression or contact pressure is demonstrated through a solved example.
Contents
8.1 Background
8.2 Functions
8.3 Adaptability
8.4 Advantages and Limitations
8.5 Materials of Construction
8.6 Drop Spillway: Components and Functions
8.7 Design of Drop Spillway
8.7.1 Hydrologic Design
8.7.1.1 Rational Method
8.7.1.2 Frequency Analysis of Historical Rainfall or Flow Data
8.7.1.3 Hydrological or Hydraulic Modelling
8.7.2 Hydraulic Design of Straight Drop Spillway
8.7.2.1 Design Cases
8.7.2.2 Design for Free Flow Condition
8.7.2.3 Design for Submerged Flow Condition
8.7.2.4 Design Dimensions of Different Components of a Straight Drop Spillway
8.7.3 Hydraulic Design of Box-Inlet Drop Spillway
8.7.3.1 Design for Free Flow Condition
8.7.3.2 Case I: When the crest of the box-inlet controls the flow
8.7.3.3 Case II: When the opening of the headwall controls the flow
8.7.3.4 Design Dimensions of Different Components of a Box-Inlet Drop Spillway
8.7.3.5 Submergence Effect
8.7.4 Structural Design of Straight Drop Spillway
8.7.4.1 Safety of the Structure against Overturning
8.7.4.2 Safety of the Structure against Sliding
8.7.4.3 Safety of the Structure against Piping
8.7.4.4 Safety of the Structure against Tension
8.7.4.5 Safety of the Structure against Compression or Contact Pressure
8.7.4.6 Apron Thickness
8.7.4.7 Wall Thickness
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 9
DROP INLET SPILLWAY
Abstract
Drop-inlet spillway, a widely used soil conservation structure, is preferred for sites providing substantial temporary storage above the inlet, especially in gullies having more than 3 m fall or drop. The chapter focuses on the hydraulic design of two general types of drop inlet spillways, the first having a circular or rectangular box type flat crest and the second having a standard or funnel-shaped crest, the latter popularly known as ‘morning glory’ or ‘glory hole’ spillway. It discusses the typical head-discharge relationships of the structure, controlled by its various components, besides the composite head-discharge relationship. The pressure distribution in various components of a drop-inlet spillway, essential for determining the hydraulic loading to ensure safety against cavitation, is discussed. The chapter mainly focuses on designing the standard-crested and the flat-crested drop inlet spillways under specific discharge and pressure conditions. The design includes computing the water surface profile in the conduit and developing the composite head-discharge relationship. The complex computations involved in the design are demonstrated through solved examples.
Contents
9.1 Background
9.1.1 Standard-Crested and Flat-Crested Drop Inlet Spillway
9.2 Functions
9.3 Adaptability
9.4 Advantages and Limitations
9.5 Materials of Construction
9.6 Drop Inlet Spillway: Components and Functions
9.6.1 Inlet or Riser
9.6.2 Conduit
9.6.3 Outlet or Terminal Structure
9.7 Design of Drop Inlet Spillway
9.7.1 Head-Discharge Relationship
9.7.2 Composite Head-Discharge Relationship
9.7.3 Hydraulic Grade Line Location at Conduit Exit
9.7.4 Pressure Distribution within the Spillway
9.7.4.1 Pressure Distribution in the Conduit Flowing Full
9.7.5 Design Approaches
9.7.5.1 Standard-Crested Drop Inlet Spillway
9.7.5.2 Flat-Crested Drop Inlet Spillway
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 10
CHUTE SPILLWAY
Abstract
A chute spillway also called a trough spillway, is designed to dispose of surplus water from upstream to downstream through a steeply sloped open channel. The chapter describes the functions of the various components of a chute spillway and presents the hydrologic, hydraulic and structural designs of chute spillways. The hydraulic design of the entrance or approach channel, inlet or control structure, chute channel or discharge carrier and outlet or energy dissipater is presented. The structural stability is analysed considering the weight of the structure and the uplift pressure created due to the differential head between the upstream and downstream. A detailed procedure to analyse the stability of the structure against overturning, tension and compression is demonstrated through a solved example.
Contents
10.1 Background
10.2 Functions
10.3 Adaptability
10.4 Advantages and Limitations
10.5 Materials of Construction
10.6 Chute Spillway: Components and Functions
10.6.1 Entrance or Approach channel
10.6.2 Inlet or Control structure
10.6.3 Chute Channel or Discharge Carrier
10.6.4 Outlet or Energy Dissipater
10.7 Design of Chute Spillway
10.7.1 Hydrologic Design
10.7.2 Hydraulic Design
10.7.2.1 Entrance or Approach channel
10.7.2.2 Inlet or Control Structure
10.7.2.3 Chute channel or Discharge Carrier
10.7.2.4 Outlet or Energy Dissipater
10.7.3 Structural Design
10.7.3.1 Safety of the Structure against Overturning
10.7.3.2 Safety of the Structure against Tension
10.7.3.3 Safety of the Structure against Compression or Contact Pressure
Practice Questions
Multiple Choice Questions
Bibliography
CHAPTER 11
WIND EROSION
Abstract
Wind erosion is a serious environmental hazard, which causes land degradation and air pollution and adversely affects human health. Dust emission generated by wind erosion is the most prominent aerosol source that directly or indirectly influences the global radiation balance. The chapter presents the factors influencing wind erosion and describes the mechanics of soil particle movement in wind erosion. The Wind Erosion Equation (WEQ), the first empirical wind erosion model for estimating the annual soil loss, and its revised version, the Revised WEQ (RWEQ), are discussed. A few popular process-based wind erosion models are introduced. The basic principles adopted for controlling wind erosion are presented. The chapter also describes the benefits of windbreaks and shelterbelts, two popular mechanical measures of wind erosion control. The design of the windbreaks and shelterbelts is discussed in terms of their height, length, continuity, density, orientation and number of rows and plant species.
Contents
11.1 Background
11.2 Factors Affecting Wind Erosion
11.3 Mechanics of Movement
11.3.1 Initiation of Movement
11.3.2 Transportation
11.3.2.1 Saltation
11.3.2.2 Suspension
11.3.2.3 Surface Creep
11.3.3 Deposition
11.4 Estimation of Soil Loss due to Wind Erosion
11.4.1 Wind Erosion Equation (WEQ)
11.4.1.1 Soil Erodibility Index, I
11.4.1.2 Soil Ridge Roughness Factor, K
11.4.1.3 Climate Factor, C
11.4.1.4 Unsheltered Length, L
11.4.1.5 Vegetative Cover Factor, V
11.4.1.6 Application of WEQ for Estimating Wind Erosion
11.4.1.7 Limitations of WEQ
11.4.2 Revised WEQ (RWEQ)
11.4.3 Process-Based Models for Wind Erosion
11.4.3.1 Wind Erosion Prediction System (WEPS)
11.4.3.2 Single-event Wind Erosion Evaluation Program (SWEEP)
11.4.3.3 Wind Erosion Stochastic Simulator (WESS)
11.4.3.4 Texas Erosion Analysis Model (TEAM)
11.4.3.5 Dust Production Model (DPM)
11.4.3.6 Wind Erosion on European Light Soils (WEELS)
11.4.3.7 Australian Land Erodibility Model (AUSLEM)
11.4.3.8 Aeolian EROsion (AERO) model
11.5 Wind Erosion Control
11.5.1 Reduce the Field Width along the Prevailing Wind Direction
11.5.1.1 Windbreaks and Shelterbelts
11.5.1.2 Grass Barriers
11.5.1.3 Artificial Barriers
11.5.1.4 Strip Cropping
11.5.2 Establish and Maintain Vegetative Cover on the Surface
11.5.3 Maintain Stable Aggregates or Clods on the Surface
11.5.4 Roughen the Land Surface
11.6 Windbreaks and Shelterbelts
11.6.1 Benefits of Windbreaks and Shelterbelts
11.6.1.1 Reduced Wind Erosion
11.6.1.2 Improved Microclimatic Conditions
11.6.1.3 Snow Retention
11.6.1.4 Reduced Wind Damages
11.6.1.5 Energy Conservation
11.6.2 Design of Windbreaks and Shelterbelts
11.6.2.1 Height
11.6.2.2 Length
11.6.2.3 Continuity
11.6.2.4 Density
11.6.2.5 Orientation
11.6.2.6 Number of Rows and Plant Species
Practice Questions
Multiple Choice Questions
Bibliography
