Hydrological cycle

The hydrological cycle, also known as the water cycle, describes the continuous movement of water on, above, and below the Earth's surface. It involves various processes such as evaporation, condensation, precipitation, infiltration, runoff, and transpiration, which redistribute water between the atmosphere, oceans, land surfaces, and groundwater reservoirs.

1. Evaporation: Evaporation is the process by which water from the Earth's surface, such as oceans, lakes, rivers, and soil, is converted into water vapour and released into the atmosphere. Solar energy heats the surface water, causing molecules to gain enough energy to overcome surface tension and escape into the air.

2. Transpiration: Transpiration is the release of water vapour from the leaves and stems of plants into the atmosphere. Plants absorb water from the soil through their roots and transport it to their leaves, where it evaporates through small openings called stomata.

3. Condensation: Condensation is the process by which water vapour in the atmosphere cools and forms liquid droplets or ice crystals. When warm, moist air rises and cools, it reaches its dew point, causing water vapor to condense around tiny particles, such as dust or aerosols, forming clouds.

4. Cloud Formation: Condensed water vapour forms clouds, which are visible accumulations of water droplets or ice crystals suspended in the atmosphere. Clouds play a crucial role in the hydrological cycle by transporting and redistributing water vapor across different regions of the Earth.

5. Precipitation: Precipitation occurs when water droplets or ice crystals in clouds grow large enough to fall back to the Earth's surface under the influence of gravity. Precipitation can take various forms, including rain, snow, sleet, and hail, depending on atmospheric conditions and temperature.

6. Infiltration: Infiltration is the process by which precipitation or surface water seeps into the soil and percolates downward through the soil layers, eventually reaching the groundwater table. Infiltrated water replenishes groundwater reserves and contributes to groundwater recharge.

7. Surface Runoff: Surface runoff is the flow of water over the land surface when precipitation exceeds the soil's infiltration capacity or when the ground is saturated. Runoff collects in rivers, streams, lakes, and oceans, transporting sediment, nutrients, and pollutants downstream.

8. Groundwater Flow: Groundwater flow refers to the movement of water through permeable rock layers and underground aquifers. Groundwater moves slowly underground, following the natural gradient from areas of higher elevation to lower elevation, eventually discharging into surface water bodies or emerging as springs.

9. Sublimation: Sublimation is the process by which ice or snow transitions directly into water vapor without passing through the liquid phase. Sublimation occurs primarily in regions with cold temperatures and low atmospheric pressure, where ice and snow can evaporate directly into the air.

10. Surface Water Evaporation: Surface water evaporation refers to the direct evaporation of water from lakes, rivers, reservoirs, and other surface water bodies exposed to sunlight and atmospheric heat. Surface water evaporation contributes to the moisture content of the atmosphere and influences regional climate patterns.

The hydrological cycle is a dynamic and interconnected system that plays a fundamental role in shaping Earth's climate, weather patterns, ecosystems, and water resources. It regulates the distribution and availability of freshwater, sustains life on Earth, and influences various natural processes and human activities.

Hydrological budget Precipitation

The hydrological budget, also known as the water balance or water budget, is a quantitative assessment of the inputs, outputs, and storage changes of water within a specific area over a defined period of time. Precipitation is a key component of the hydrological budget as it represents one of the primary inputs of water into a hydrological system.

How precipitation fits into the hydrological budget:

1. Precipitation (P):

   • Precipitation refers to the amount of water, in the form of rain, snow, sleet, or hail, that falls from the atmosphere to the Earth's surface within a given area and time period. Precipitation is the primary input of water into the hydrological system and plays a crucial role in replenishing surface water bodies, groundwater reserves, and soil moisture.

2. Other Components of the Hydrological Budget:

   • Evaporation (E): Evaporation represents the loss of water from the Earth's surface back to the atmosphere in the form of water vapor. It occurs from surface water bodies, soil moisture, and vegetation.
   • Transpiration (T): Transpiration is the release of water vapor from the leaves and stems of plants into the atmosphere during photosynthesis.
   • Runoff (R): Runoff refers to the flow of water over the land surface and into rivers, streams, lakes, and oceans. It includes both surface runoff and subsurface flow.
   • Infiltration (I): Infiltration is the process by which precipitation or surface water seeps into the soil and percolates downward to recharge groundwater.
   • Groundwater Flow (G): Groundwater flow represents the movement of water through underground aquifers and rock layers.
   • Storage Change (ΔS): Storage change reflects the change in water volume stored within the hydrological system, including changes in surface water bodies, soil moisture, and groundwater levels.

3. Hydrological Budget Equation:

   • The hydrological budget equation can be expressed as: P = E + T + R + I + G + ΔS
   • In this equation, the total precipitation (P) represents the sum of all water inputs into the system, which are balanced by the outputs (evaporation, transpiration, runoff, infiltration, groundwater flow) and changes in storage over time.

4. Assessment and Management:

   • By quantifying the various components of the hydrological budget, hydrologists and water managers can assess water availability, identify sources of water stress or surplus, and develop strategies for sustainable water management, such as water conservation, irrigation management, and flood control measures.

Overall, precipitation is a fundamental component of the hydrological budget that drives the water cycle and influences the availability and distribution of water resources within a region. Understanding the role of precipitation in the hydrological budget is essential for effective water resource management and planning.

Drainage system

A drainage system is a network of structures, channels, and infrastructure designed to manage the flow of surface water and remove excess water from urban, rural, and agricultural areas to prevent flooding, erosion, and waterlogging. Drainage systems play a critical role in maintaining the stability and functionality of landscapes, infrastructure, and communities by controlling the movement of water and minimising the risks associated with water-related hazards.

Closed and open drainage systems are two distinct approaches to managing surface water runoff, wastewater, and stormwater in urban and rural environments.

1. Closed Drainage System

   • A closed drainage system, also known as a piped drainage system, is a network of underground pipes, conduits, and culverts designed to collect, convey, and discharge water runoff away from populated areas and infrastructure. In a closed system, the flow of water is enclosed within pipes, tunnels, or channels, minimizing exposure to the surface and reducing the risk of flooding, erosion, and water quality degradation.

   Key Features

   • Pipes and Conduits: Closed drainage systems consist of pipes made of materials such as concrete, plastic, or metal, which are buried underground to collect and transport water runoff.
   • Culverts: Culverts are structures installed under roads, railways, or embankments to allow the passage of water runoff beneath obstructions.
   • Manholes: Manholes provide access points to underground pipes for inspection, maintenance, and repairs.
   • Detention Basins: Some closed drainage systems may include detention basins or underground storage tanks to temporarily store and regulate the flow of stormwater runoff during peak periods.

   Benefits

   • Reduces surface water runoff and minimizes the risk of flooding.
   • Protects infrastructure, buildings, and roads from water-related damage.
   • Improves water quality by reducing pollutant runoff and sedimentation.
   • Provides a discreet and unobtrusive drainage solution suitable for urban areas with limited space.

2. Open Drainage System

   • An open drainage system, also known as a surface drainage system or natural drainage system, relies on natural or engineered surface features such as ditches, swales, channels, and ponds to manage water runoff and convey it to suitable discharge points. In an open system, the flow of water remains visible and exposed to the surface, allowing for natural infiltration, evaporation, and treatment processes.

   Key Features

   • Ditches and Swales: Open drainage systems utilize shallow channels or ditches along roadsides, fields, or properties to collect and channel water runoff.
   • Natural Watercourses: Natural watercourses such as rivers, streams, and creeks serve as conveyance channels for surface water runoff in open drainage systems.
   • Retention Ponds: Open drainage systems may include retention ponds or wetlands to capture, store, and treat stormwater runoff before discharging it to surface water bodies.

   Benefits

   • Utilizes natural hydrological processes and landforms to manage water runoff.
   • Enhances groundwater recharge and supports ecosystem functions.
   • Provides habitat for wildlife and promotes biodiversity.
   • Offers cost-effective and low-maintenance drainage solutions suitable for rural and environmentally sensitive areas.

Types of Drainage System

1. Sanitary Drainage System: A sanitary drainage system is designed to collect and convey wastewater from buildings and structures to a treatment facility or septic system for disposal or treatment. It primarily handles wastewater from sinks, toilets, showers, and appliances within residential, commercial, and industrial properties. The system includes pipes, fittings, traps, vents, and manholes to ensure the safe and efficient removal of sewage while preventing the entry of foul odors, gases, and pathogens into occupied spaces.

   

2. Stormwater Drainage System: A stormwater drainage system is designed to manage the collection and conveyance of rainwater runoff from streets, roofs, parking lots, and other impervious surfaces to prevent flooding and erosion. It includes features such as stormwater drains, catch basins, pipes, culverts, detention basins, and green infrastructure to control the flow, volume, and quality of stormwater runoff. Stormwater drainage systems help protect infrastructure, property, and the environment by reducing the risk of urban flooding, water pollution, and damage from heavy rain events.

   

3. Combined Drainage System: A combined drainage system is a single network of pipes and conduits that collects and transports both sanitary sewage and stormwater runoff to a treatment facility or discharge point. Unlike separate systems, which handle sewage and stormwater separately, combined systems integrate both flows into a common infrastructure. While combined drainage systems can be cost-effective and space-saving, they may pose challenges during heavy rain events when the capacity of the system is exceeded, leading to combined sewer overflows (CSOs) and water pollution incidents.

   

4. Subsoil Drainage System: A subsoil drainage system, also known as a subsurface drainage system or under drain system, is designed to remove excess water from the soil and groundwater table to improve soil stability, prevent water logging, and control soil salinity. It typically consists of perforated pipes, drainage tiles, or trenches installed below the ground surface to collect and divert groundwater away from foundations, basements, fields, and infrastructure. Subsoil drainage systems are commonly used in agricultural, residential, and civil engineering projects to manage groundwater levels and maintain soil health.

   

5. Sump Pump System: A sump pump system is a mechanical device used to remove accumulated water from a sump pit or basin, typically found in basements, crawl spaces, or low-lying areas prone to water intrusion. The sump pump activates automatically when water levels rise above a certain threshold, pumping water away from the property to a safe discharge point, such as a storm drain or exterior area. Sump pump systems help prevent basement flooding, groundwater seepage, and moisture-related damage to buildings and foundations.

   

Benefits of Drainage Systems

1. Flood Prevention and Mitigation

2. Erosion Control

3. Improved Water Quality

4. Infrastructure Protection

5. Agricultural Productivity

6. Public Health and Safety

7. Urban Development and Land Use Planning

8. Economic Benefits

Surface runoff & Stream flow estimation

RUNOFF

Run off can be described as the part of the water cycle that flows over land as surface water instead of being absorbed into groundwater or evaporating.

Three types of run off :-

1) Surface runoff

2) Interflow runoff

3) Base flow runoff

Total Runoff = Surface runoff (including sub-surface runoff) + Base flow

Surface Runoff

It is that portion of rainfall, which enters the stream immediately after the rainfall.

Sub surface (interflow ) Runoff

That part of rainfall, which first enters into the soil and moves laterally without joining the water-table to the streams, rivers or oceans, is known as sub-surface runoff or inter flow. It takes very little time to reach the river or channel in comparison to ground water.

Base flow ( ground water flow)

It is delayed flow, part of rainfall, which after falling on the ground surface, infiltrates into the soil and meets to the water-table; and flow to the streams, oceans etc. It takes a long time to join the rivers or oceans, say for as years.

Channel runoff (Streamflow)

It is the flow of water in streams and other channels. The discharge of water flowing in a channel is measured using stream gauges or can be estimated by the Manning equation. It is measured in units of discharge (m3/s). Stream flow rate determined by Q= V/T

Stream flow measurement is done by :- stage measurement ,velocity measurement, discharge measurement

The direct methods of measurement of stream discharge include:

a. Area velocity methods

b. Dilution techniques

c. Electromagnetic method

d. Ultrasonic method

Manual gauges

Stage measurement is carried out using staff gauge (manual gauge) The manual gauge is fixed to a structure like bridge abutment, pier. It should be vertical with no inclination, the markings should be clear.

Automatic stage recorders

A float gauge recorder is typically housed in a stilling well. The float is balanced with a counter weight over a pulley system which is attached to a recorder. The displacement of the float due to change in water surface elevation causes an angular displacement in the pulley, which causes movement in the recorder. The recorder records stage versus time data continuously. The stage recorder is placed above the highest water level that may be reached at that site.

Bubble gauge type recorder

Bubble gauge type recorder is used in which case compressed air or gas bubble is released through an outlet placed at the bottom of the stream. The advantage of such recorders is that it does not need a stilling well arrangement and the recorder assembly can be placed far away from the stream. 

Stage data

(Stage hydrograph) is in the form of stage against chronological time. Important in design of hydraulic structures, flood warning and flood protection work.

Measurement of velocity

Velocity can be measured directly, using a flowmeter (essentially a speedometer for water.

Current meters :- it essentially consist of a rotating element which rotates due to the reaction of the stream current with an angular velocity proportional to the stream velocity. It is used to measure velocity at a point across the cross section of the stream

Two types of current meters :- vertical axis meters & horizontal axis meters

The vertical axis current meter consists of a series of conical cups mounted on a vertical axis .The conical cups fill with water and start rotating, this helps in the stream velocity measurement.

Horizontal axis meters consist of a propeller mounted at the end of horizontal shaft. It has a provision to count the number of revolutions in a known interval of time. This is accomplished by making & breaking of an electric circuit either mechanically or electro-magnetically at each revolution of the shaft. Revolutions per second is calculated by counting the number of such signals in a known interval of time.

Area velocity method

• To determine the discharge of the stream at the selected cross-sectional area otherwise called the gauging site.

• The stream is divided into sections & at each of these sub sections the average velocity (distance/time)( by current meter mainly)is measured.

• The area of the sub section is determined by measuring the depth and the width of the subsection. The discharge (Q=V*A) at each of these

subsections is the cross-sectional area multiplied by the average velocity at the sub section .

• The discharge estimation at the gauging site is the summation of all these individual discharges. Discharge is the volume of water flowing through the

stream or river at a certain time.

Q= AV

Q = discharge ( m3 /s) (cumec)

A = cross sectional area ( m2)

V = velocity ( m/s)

Rating curve plots the discharge measured by area velocity method on the y axis and the measured stage depth at the gauging station on the x axis.

Hydrograph :-plots discharge of river over time

Dilution technique of stream flow

• It depends on continuity principle.

• Methods:- Sudden injection & constant rate injection method.

• It uses tracers which may be chemicals (NaCl, Na2Cr2o7), fluorescent dyes(rhodamine-WT) or radioactive materials(Br-82, Na-24,I-132). An initial high quantity of tracer is mixed in a small discharge and then the concentration of the diluted quantity is measured at another section using steady state continuity equation.

Electromagnetic flow meter is used to measure flows in tidal streams/channels where is fluctuation in quantity and direction of flow. The minimum detectable velocity in this case is 0.005m/s. They can also be used for cross sections which are disturbed by weed growth and sedimentation

Ultrasonic method of velocity measurement of flow It uses two transducers fixed at two banks of the river or channel, receive and send ultrasonic signals. Time taken from one end to another is different. In one case the component of flow velocity in the direction of the sound waves is added to the velocity of sound, while other bank the flow velocity component is subtracted.

The difference in the two velocity components since it can be measured, and the width of the stream is known, the velocity of flow can be determined.

Used for unstable cross sections, which have fluctuating weed growth sections, high suspended solids in flow and there is rapid change in magnitude and direction of flow.

Stage discharge relationship (rating curve)

Measured value of discharge plotted against the corresponding stage

Indirect measurement of flow :- weirs

A weir is a small wall(thin steel plate , concrete & erosion resistant ) constructed across the width of the stream to create an obstruction to flow to measure discharge.

Two types :- V notch type weir & rectangular weir

Rainfall-runoff relationship

The rainfall-runoff relationship for any rainstorm depends on the dynamic interaction between rain intensity, soil infiltration and surface storage.

Runoff occurs whenever rain intensity exceeds the infiltration capacity of the soil

Runoff from a given rainstorm is a function of:

i.Rainfall intensity distribution and sequence, during a particular rainstorm event

ii.Soil infiltration rates

iii.The soil surface storage capacity

Factors Affecting Runoff:

Climatic factors 

1. Type of precipitation 
2. Rainfall intensity
3.  Duration of rainfall
4.  Rainfall distribution
5.  Direction , velocity of prevailing wind
6. Annual rainfall 
   

Physiographic factors

1. Size of watershed
2. Shape of watershed
3. Slope of watershed
4. Orientation of watershed
5.  Land use
6. Soil moisture & type

Runoff Processes 

1. The paths water can take in moving to a stream are illustrated in Figure 1. Precipitation may be in the form of rain or snow. Vegetation may intercept some fraction of precipitation. Precipitation that penetrates the vegetation is referred to as throughfall and may consist of both precipitation that does not contact the vegetation, or that drops or drains off the vegetation after being intercepted.
2. A large fraction of intercepted water is commonly evaporated back to the atmosphere. There is also flux of water to the atmosphere through transpiration of the vegetation and evaporation from soil and water bodies.
3. The surface water input available for the generation of runoff consists of throughfall and snowmelt. This surface water input may accumulate on the surface in depression storage, or flow overland towards the streams as overland flow, or infiltrate into the soil, where it may flow laterally towards the stream contributing to interflow.
4. Infiltrated water may also percolate through deeper soil and rock layers into the groundwater. The water table is the surface below which the soil and rock is saturated and at pressure greater than atmospheric. This serves as the boundary between the saturated zone containing groundwater and unsaturated zone. Water added to the groundwater is referred to as groundwater recharge.
5. Immediately above the water table is a region of soil that is close to saturation, due to water being held by capillary forces. This is referred to as the capillary fringe.
6. Lateral drainage of the groundwater into streams is referred to as baseflow, because it sustains streamflow during rainless periods.
7. Subsurface water, either from interflow or from groundwater may flow back across the land surface to add to overland flow. This is referred to as return flow. Overland flow and shallower interflow processes that transport water to the stream within the time scale of approximately a day or so are classified as runoff.
8. Water that percolates to the groundwater moves at much lower velocities and reaches the stream over longer periods of time such as weeks, months or even years. The terms quick flow and delayed flow are also used to describe and distinguish between runoff and baseflow.
9. Runoff includes surface runoff (overland flow) and subsurface runoff or subsurface stormflow (interflow). 

Erosion control and Water conservation

Erosion Control

Erosion is the process by which soil and rock are removed from the Earth's surface by natural processes such as wind or water flow, often accelerated by human activities like deforestation or construction.

Principles of Erosion Control 

1. It is better to control the initiation of soil erosion than reclaim an eroded land. For this purpose, every piece of land in a watershed should be used properly in accordance with its capability. 
2. Land should be used in such a manner so that no erosion or deterioration of land takes place even after prolonged use.  
3. Suitable agronomical practiced should be followed to protect the land from the energy of the falling raindrop and surface flow.  
4. Different tillage and agronomical practices are required to be followed to achieve the desired effects.

Erosion control involves strategies to prevent or mitigate this loss of soil, which is vital for agriculture, ecosystem health, and infrastructure stability. Some erosion control methods include: 

Contour Cropping

1. Contour Cropping is a conservation farming method that is used on slopes to control soil losses due to water erosion. 
2. Contour cropping involves planting crops across the slope instead of up and down the slope. 
3. Use of contour cropping protects the valuable topsoil by reducing the velocity of runoff water and inducing more infiltration. 
4. Contour cropping is most effective on slopes between 2-10 %.

Strip Cropping

1. Strip Cropping is the practice of growing strip of crops having poor potential for erosion control, such as root crop, cereals, etc. alternated with strips of crops having good potentials for erosion control, such as fodder crops, grasses, etc., which are close growing crops. 
2.  Strip cropping is a more intensive farming practice than contour farming. 
3.  Strip cropping is laid out by using the three methods:

Contour Strip Cropping: In contour strip cropping, alternate strips of crop are sown more or less following the contours, similar to contouring. Suitable rotation of crops and tillage operations are followed during the farming operations.

Field Strip Cropping: In a field layout of strip cropping, strip of uniform width are laid out across the prevailing slope, while protecting the soil from erosion by water. To protect the soil from erosion by wind, strips are laid out across the prevailing direction of wind. Such practices are generally followed in areas where the topography is very irregular, and the contour lines are too curvy for strict contour farming.

Buffer Strip Cropping: Buffer strip cropping is practiced where uniform strip of crops are required to be laid out for smooth operations of the farm machinery, while farming on a contour strip cropping layout. Buffer strip of legumes, grasses and similar other crops are laid out between the contour strips as correction strips. Buffer strips provide very good protection and effective control of soil erosion. 

Mulching

1. Mulch is any material that is spread or laid over the surface of the soil as a covering. 
2. Mulches are used to minimise rain splash, reduce evaporation, control weeds, reduce temperature of soil in hot climates, and moderate the temperature to a level conducive to microbial activity.
3. It also helps in breaking the energy of raindrops, prevent splash and dissipation of soil structure, obstruct the flow of runoff to reduce their velocity and prevent sheet and rill erosion. 
4. They also help in improving the infiltration capacity by maintaining a conductive soil structure at the top surface of land. 1. Bunding 2. Terracing

Mechanical practices are engineering measures used to control erosion from slopping land surfaces and thus land surface modification is done for retention and safe disposal of runoff water. In the design of such practices, the basic approach is:

To increase the time of stay of runoff water in order to increase the infiltration time for water.

To decrease the effect of land slope on runoff velocity by intercepting the slope at several points so that the velocity is less than the critical velocity.  

To protect the soil from erosion caused by the runoff water. 

Bunding Methods 

Bund is an engineering measure of soil conservation, used for creating obstruction across the path of surface runoff to reduce the velocity of flowing water.  It retains the running off water in the watershed and thus to helps to control soil erosion. Bunds are simply embankment like structures, constructed across the land slope. 

Different Types of Bunds 

Contour bund:  When the bunds are constructed along the contours with some minor deviation to adapt to practical situation, they are known as contour bunds. Contour bunds are recommended for areas with low annual rainfall (< 600 mm) , permeable soils and land slope of less than 6%. The main functions of contour bunds are: 1. It reduces the length of slope which in turn reduces the soil erosion. 2. The water is impounded for some time and gets recharged into the soil which helps in crop cultivation.

Contour bunds are of two types: 1. Narrow base 2. Broad base 

Narrow Base 

a) Narrow base contour bunding system, there is an obstruction for crossing of farm implements; natural vegetations cover the sides and more height is allowed for same cross-section. 

b) It has limitations that, there is considerable area is lost in constructing the bund; the bund section is liable to get affected by erosion due to rain drop impact, hence requires a sincere maintenance. 

c) The narrow base contour bund also causes obstruction in farming operations. 

Broad base 

a) The broad base contour bunding is concerned, it does not create hindrance in farming operations; the entire area can be kept under cultivation. 

b)  It has some limitations, such as disturbance of bund’s section due to crossing of farm equipments, as result there is required an attentive care and maintenance.

c) Apart from above, the soil of bund is also loosened during movement of farm machineries, causing reduction in the size of bund in a very short period, unless some proper maintenance is adopted.

Graded bunds: If the bunds are constructed with some slope, they are known as graded bunds. The choice of the types of bund is dependent on land slope, rainfall, soil type and purpose of the bund in the area.

1) Graded bund system is designed to dispose of excess runoff safely from agricultural fields. 

2) A graded bund is laid out with a longitudinal slope gradient leading to outlet. 

3) Variations in the grade are provided at different sections of the bund to keep the runoff velocity within the desired limits so as not to cause any soil erosion. Graded bunds are laid out in areas where - The land is susceptible to water erosion - The area has water logging problems - High rainfall (>600 mm) and Relatively impervious soil.

Terracing 

1) Terrace is an earth-embankment, constructed across the slope, to control runoff and minimise soil erosion loss at highly slopping land (slope >10%).  

2) A terrace acts as an intercept to land slope, and divides the sloping land surface into strips. 

3) Terraces are classified into to two major types:

1. Broad-base terraces    2. Bench terraces

 Broad-base terraces are adapted where the main purpose is either to remove or retain water on sloping land suitable for cultivation. The purpose of bench terraces is mainly to reduce the land slope.

 Bench Terrace Components

The original bench terrace system consists of a series of flat shelf-like areas that convert a steep slope of 20 to 30% to a series of level, or nearly level benches. In other words, bench terracing consists of construction of series of platforms along contours cut into hill slope in a step like formation. These platforms are separated at regular intervals by vertical drop or by steep sided and protected by vegetation and sometimes packed by stone retaining walls. In hilly areas bench terraces is used for the purpose of converting hill slopes to suit agriculture.  In some areas where the climatic conditions favour the growing of certain cash crops like potato, coffee, the hill slopes are to be bench terraced before the area is put for cultivation of these crops. It also been adopted for converting sloping lands into irrigated fields or for orchard plantations.

Types of Bench

Terraces Depending on the purpose for which they are used, bench terraces are also classified as follows: 

1. Hill-type bench terraces: used for hilly areas with a grade reversely towards the hill. 

2. Irrigated bench terraces: level benches adopted under irrigated conditions. 

3. Orchard bench terraces: narrow width terraces for individual trees. 

Water Conservation

 Water conservation refers to the efficient use and management of water resources to reduce waste and ensure sustainability. This is particularly important in regions facing water scarcity or where demand exceeds the available supply. Water conservation practices include:

Efficient irrigation: Using drip irrigation systems or timed sprinklers to deliver water directly to plant roots, minimising evaporation and runoff.

Rainwater Harvesting: Collecting rainwater from rooftops or other surfaces for later use in irrigation or household activities.

Low Flow Fixtures: Installing low-flow toilets, shower heads, and faucets to reduce water usage in homes and buildings.

Xeriscaping: Landscaping with native plants that require minimal water, reducing the need for irrigation.

Water Recycling: Treating and reusing wastewater for non-potable purposes like irrigation or industrial processes.

Water Quality Management- Principles of water quality

Water quality management involves understanding, monitoring, and regulating the chemical, physical, and biological characteristics of water to ensure its suitability for various uses, such as drinking, recreation, agriculture, and ecosystem health. Several principles guide water quality management:

1. Water Quality Standards: Establishing standards and guidelines for acceptable levels of contaminants and parameters in water bodies based on their designated use. These standards often include limits for pollutants such as heavy metals, nutrients, pathogens, and chemicals.

2. Pollution Prevention: Emphasising the prevention of pollution at its source through regulations, best management practices, and public education. This approach aims to minimise the introduction of harmful substances into water bodies and reduce the need for costly remediation efforts.

3. Monitoring and Assessment: Regularly monitoring water quality through sampling and analysis to assess current conditions, identify trends, and detect emerging issues. Monitoring helps authorities make informed decisions about water management strategies and prioritise areas for remediation or protection.

4. Integrated watershed management: Recognising that water quality is influenced by activities and land use practices within entire watersheds. Integrated watershed management involves coordinating efforts across multiple sectors to address pollution sources, manage runoff, and protect water resources holistically.

5. Treatment and Remediation: Employing treatment technologies and restoration measures to improve water quality in impaired or polluted water bodies. This may include physical, chemical, or biological processes to remove contaminants, restore habitat, or enhance natural filtration and purification mechanisms.

6.  Public participation and Education: Engaging stakeholders, including communities, businesses, and policymakers, in water quality management efforts. Public participation fosters support for conservation initiatives, increases awareness of water issues, and encourages responsible behaviour to protect water resources.

7. Adaptive Management: Adopting flexible and iterative approaches to water quality management that allow for adjustments based on new information, changing conditions, and evolving priorities. Adaptive management emphasises continuous learning, experimentation, and collaboration to achieve long-term environmental sustainability.

8. Ecosystem Based Approaches: Recognising the interconnectedness of ecological processes and human activities in shaping water quality outcomes. Ecosystem-based approaches prioritise the preservation and restoration of natural habitats and functions to support healthy aquatic ecosystems and enhance water quality.

Water quality refers to the basic physical, chemical and biological characteristics of water that determine its suitability for life or for human uses. The acceptable quality of water varies with its intended use. The characteristics of water can be classified into three broad categories:

1. Physical Characteristics: temperature, colour, odour, turbidity and solids

2. Chemical Characteristics: pH, conductivity, salinity, hardness, BOD

3. Biological Characteristics: counts of specific organisms and groups of organisms

Physical Characteristics

Temperature: Temperature is a measure of the average energy (kinetic) of water molecules. It is measured on a linear scale of degrees Celsius or degrees Fahrenheit. Temperature is a basic water quality variable. It determines the suitability of water for various forms of aquatic life. Depending on the geographic location the mean annual temperature varies in the range of 10 to 21^oC with an average of 16^oC. Temperature affects a number of water quality parameters such as dissolved oxygen which is a chemical characteristic.

Colour: Colour in water is primarily a concern of water quality for aesthetic reason. Colored water give the appearance of being unfit to drink, even though the water may be perfectly safe for public use. Color of the water body can indicate the presence of organic substances, such as algae or humic compounds. In recent times, colour has been used as a quantitative assessment of the presence of potentially hazardous or toxic organic materials in water.

Taste and Odour: Taste and odour are human perceptions of water quality. Human perception of taste includes sour (hydrochloric acid), salty (sodium chloride), sweet (sucrose) and bitter (caffeine). Relatively simple compounds produce sour and salty tastes. However, sweet and bitter tastes are produced by more complex organic compounds. Odor is produced by gas production due to the decomposition of organic matter or by substances added to the wastewater. 

Turbidity: Turbidity is a measure of the light-transmitting properties of water and is comprised of suspended and colloidal material. It is important for health and aesthetic reasons. Transparency of natural water bodies is affected by human activity, decaying plant matter, algal blooms, suspended sediments, and plant nutrients.

Solids: Total dissolved solids (TDS) is the term used to describe the inorganic salts and small amounts of organic matter present in solution in water. The principal constituents are usually calcium, magnesium, sodium, and potassium cations and carbonate, hydrogen carbonate, chloride, sulfate, and nitrate anions. The total solids content of water is defined as the residue remaining after evaporation of the water and drying the residue to a constant weight at 103°C to 105°C.

Chemical Characteristics

pH: pH is a measure of how acidic or basic (alkaline) the water is. It is defined as the negative log of the hydrogen ion concentration. The pH scale is logarithmic and ranges from 0 (very acidic) to 14 (very alkaline). 

Electrical Conductivity: The conductivity of water is an expression of its ability to conduct an electric current as a result of breakdown of dissolved solids into positively and negatively charged ions. The major positively charged ions are sodium (Na+), calcium (Ca⁺²), potassium (K⁺ )and magnesium (Mg⁺²).

 Salinity is a measure of the amount of salts in the water. Because dissolved ions increase salinity as well as conductivity, the two measures are related. The salts in sea water are primarily sodium chloride (NaCl). However, other saline waters owe their high salinity to a combination of dissolved ions including sodium, chloride, carbonate and sulfate.

Alkalinity: The alkalinity of natural water is generally due to the presence of bicarbonates formed in reactions in the soils through which the water percolates. It is a measure of the capacity of the water to neutralize acids and it reflects its buffer capacity. It may also be attributed to the presence of carbonates and hydroxides. Alkalinity is important for fish and aquatic life because it protects or buffers against rapid pH changes.

Hardness: Hardness is a natural characteristic of water which can enhance its palatability and consumer acceptability for drinking purposes. The hardness of water is due to the presence of calcium and magnesium minerals that are naturally present in the water.

The following is a measure of hardness (expressed in mg/l as CaCO₃):

Soft: 0 - 100 mg/l as CaCO₃

Moderate: 100 - 200 mg/l as CaCO₃

Hard: 200 - 300 mg/l as  CaCO₃

Very hard: 300 - 500 mg/l as CaCO₃

Extremely hard: 500 - 1,000 mg/l as  CaCO₃

Major ions in Water: There are various kinds of trace ions in water supply that influence chemical nature and account for the bulk of natural water mineral content. Most of the dissolved, inorganic chemicals in freshwater occur as ions. 

Heavy Metals: Heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentration. The some major examples of heavy metals are mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), nickel (Ni), copper (Cu), cobalt (Co) and lead (Pb) etc.

Dissolved Oxygen: Dissolved oxygen is the amount of gaseous oxygen (O₂) dissolved in an aqueous solution. It gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. The oxygen in dissolved form is needed by most aquatic organisms to survive and grow.

Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand the amount of dissolved oxygen required by aerobic biological organisms to degrade the organic material present in a water body at certain temperature over a specific time period. It widely used as an indication of the organic quality of water and thus representing the pollution load. It is most commonly expressed in milligrams of oxygen consumed per litre of sample during 5 days (BOD5) of incubation at 20°C.

Chemical Oxygen Demand

Chemical Oxygen Demand (COD) determines the quantity of oxygen required to oxidize the organic matter present in water body under specific conditions of oxidizing agent, temperature and time. COD is an important water quality parameter as it provides an index to assess the effect discharged wastewater will have on the receiving environment. 

Biological Characteristics

Microbial Contamination: Microbial contamination is one of the major concerns of water quality. Many types of microorganisms are naturally present in the water such as

Protozoans -Amoeba, cryptosporidium, giardia

Bacteria – Salmonella, typhus, cholera, shigella

Viruses –Polio, hepatitis A, meningitis, encephalitis

Helminths –Guinea worm, hookworm, roundworm

Fecal Matter

Total Coliform and Fecal Coliform

Total coliform bacteria, fecal coliform bacteria, and E. coli are all considered indicators of water contaminated with fecal matter. Contaminated water may contain other pathogens (micro-organisms that cause illness) that are more difficult to test for. Therefore these indicator bacteria are useful in giving us a measure of contamination levels. E. coli is a bacterial species found in the fecal matter of warm blooded animals (humans, other mammals, and birds).