Hydrology

Percolation

is the movement of water through the soil itself.

water table

Is the upper surface of this underground water

Infiltration

is the process by which water on the ground surface enters the soil. Fast at beginning and slow at later stages.

Infiltration

takes place at uppermost stratum of soil and movement is vertical . It is measured in inches per hour or millimeters per hour.

Percolation

is the process of a liquid slowly passing through a filter.

Percolare

It means "to strain through."

Percolation

comes from the Latin word percolare, which means "to strain through."

Percolation

happens at deeper depth when water move vertically to join water table. Usually slower compared to infiltration

Watershed

is an area on land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel.

Importance of watershed

Watersheds are important for providing clean drinking water, supporting biodiversity, and regulating the water cycle. They also play a key role in preventing erosion, reducing flooding, and maintaining water quality.

Drainage basin

Area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water

irrigation

refers to the artificial application of water and land to assist in the growth of agricultural crops.

Use of Irrigation

ensures that crops receive adequate moisture during periods of insufficient rainfall, promoting optimal growth and yield.

Irrigation systems

are designed to distribute water efficiently across agricultural fields, utilizing methods such as surface irrigation, sprinkler systems, and drip irrigation.

Importance not Irrigation

essential for sustaining agriculture in arid regions and for enhancing crop production in areas with variable rainfall patterns

Factors Influencing Irrigation Method Selection

1. Soil Characteristic,

2. Topography,

3. Water Availability,

4. Crop Type, &

5. Climate Conditions

Soul Characteristics

1. Sandy Soil

2. Clay Soil

Sandy Soil

With high infiltration rates and low water-holding capacity, these soils benefit from frequent, light applications of water. Methods like sprinkler or drip irrigation are often preferred to provide controlled moisture levels.

Clay Soil

Have lower infiltration rates but higher water retention. Surface irrigation methods, such as basin or furrow irrigation, can be effective, allowing water to infiltrate slowly and evenly.

Topography

1. Steep/Uneven SlopesSlopes

2. Flat Terrain

Steel/Uneven Slope

These areas may experience runoff and erosion with surface irrigation. Sprinkler or drip system are more suitable as they apply water more uniformly and can be adjusted to the terrain.

Flat terrain

Such areas are conducive to surface irrigation methods, where gravity aids in water distribution

Water availability

The source, quantity,and quality of water are crucial.

Crop type

Different plants have varying water needs and tolerances.

Climate conditions

Local weather patterns influence evaporation rates and water needs

CIVIL ENGINEERING INFRASTRUCTURE FOR IRRIGATION

1. Diversion Dam

2. Canal Network

3. Water Reservoir Dam

4. Lift Irrigation System

Hydraulic structures

are artificial designs that help engineers manage, control, and utilize water resources efficiently.

Importance of Hydraulic Structures

Such structures of great importance for civil engineers and water managers in diverting currents, preventing floods, and holding back water for special purposes

Importance of Irrigation

• Enhancing Crop Productivity

• Mitigaging Drought Impact

• Climate conditions

• Environmental Conservation

• Socio-Economic Benefits

PHYSICAL PROPERTIES IN DETERMINATION OF WATERSHED

• Topography

• Drainage patterns

• Soil characteristics

• Land use or land cover

• Geology

Topography

The shape and features of the land surface, including hills, valleys, ridges, and slopes, dictate the direction of water flow.

Drainage patterns

The arrangement of rivers, streams, and other watercourses within an area reveals how surface water converges and diverges.

Soil characteristics

Soil type and composition influence water infiltration rates and runoff potential. Permeable soils, like sandy soils, allow more water to infiltrate, reducing surface runoff, whereas impermeable soils, such as clay, increase runoff.

Land use / Land cover

Human activities and natural vegetation cover affect the hydrological response of a watershed.

Geology

The underlying rock formations and geological structures impact groundwater flow and surface water interactions.

Green-Ampt (GA) model

assumes a homogeneous soil with

constant hydraulic conductivity,

initial water content, and head at

the wetting front (see schematic

below). The saturated wetting

front is assumes to move

downwards as a single piston

like displacement.

Potential infiltration.

Sufficient amount of water is available for infiltration.

Ponding time (tp).

Time elapsed between the time at which the rainfall begins and the time water begins ponding on the soil surface.

Ponding Time

the time it takes for surface water to accumulate and pool on a soil surface after rainfall begins, when the infiltration rate is less than the rainfall intensity

Evapotranspiration

Refers to the sum of evaporation from the land surface plus plant transpiration from the surface to the atmosphere.

Evapotranspiration

This process is crucial in the water cycle as it represents the movement of water from the soil and plants into the air, significantly influencing water availability in ecosystems.

Evaporation

occurs when water turns into vapor from soil and water surfaces.

Transpiration

involves the release of water vapor from plant leaves.

Evapotranspiration

Composed of Evaporation and Transpiration

Potential Evapotranspiration

is the amount of evaporation that will occur if an unlimited amount of water is available.

Actual Evapotranspiration

is the actual amount of evaporation that occurs when water is limited.

Net Evaporation

Ceases when the air have reached the saturation vapor pressure

Vapor pressure deficit

Rate of evaporation is driven by

Latent heat of evaporation

The energy needed by a molecule to penetrate the water surface

Evaporation from bare soil

1. Soil is at or near saturation

2. Falling stage

Soil is at or near saturation

Evaporation is controlled by heat energy. 90% of maximum Potential Evapotranspiration (PET)

Falling stage

Surface start to dry and evaporation occurs between the soil surface. Controlled by soil properties rather than weather condition.

Interception

The water retained on plant surfaces during and after precipitation.

10-25%

How many percentage Is intercepted during precipitation annually?

Plant transpiration

Is reduced by the amount of intercepted water to be evaporated.

Transpiration

The loss of water in the form of water from plants.

Evaporation

Change of water from liquid to gas

Factors that affects transpiration rate

1. Type of plant

2. Wind

3. Plant available water

Field capacity

Amount of water remaining in the soil after gravitation flow has stopped.

Wilting point

The amount of water in the soil at 15 bars of suction.

Plant available water

The amount of water in the soil that can readily be absorb by the plant's roots.

Transpiration ratio

The ratio of the the rate of the water transpired to the dry weight of plant.

Consumptive use

The amount of water needed to grow a crop

Importance of water cycle

Evapotranspiration is a critical component of the water cycle, transferring water from land and vegetation to the atmosphere. This process balances precipitation and runoff, impacting local and regional climates. It contributes to cloud formation and precipitation patterns, ensuring that ecosystems receive adequate moisture for their survival. Additionally, it helps recharge groundwater supplies by modulating surface water levels.

Impact ofn watershed management

Effective watershed management relies on understanding evapotranspiration patterns. By accurately measuring ET, managers can assess water availability, plan irrigation schedules, and implement strategies for drought management. Recognizing how ET affects surface and groundwater interactions enables better water resource allocation and conservation efforts, enhancing sustainability in catchment areas.

Rainfall

is the primary source of water for runoff generation over the land surface.

Runoff

means the draining or flowing off of precipitation from a catchment area through a surface channel.

“Surface runoff”

When rainfall exceeds the infiltration rate at the surface, excess water begins to accumulate as surface storage in small depressions. As depression storage begins to fill, overland flow or sheet flow may begin to occur and this flow is called as

Overland Flow or Surface Runoff

The water that travels over the ground surface to a channel. The amount of surface runoff flow may be small since it may only occur over a permeable soil surface when the rainfall rate exceeds the local infiltration capacity.

Interflow

The precipitation that infiltrates the soil surface and move laterally through the upper soil layers until it enters a stream channel. Part of the precipitation that infilters moves laterally through upper crusts of the soil and returns to the surface at some location away from the point of entry into the soil.

Interflow

Also known as through flow, storm seepage, subsurface storm flow or quick return low.

Groundwater Flow or Base Flow

The portion of precipitation that percolates downward until it reaches the water table. This water accretion may eventually discharge into the streams if the water table intersects the stream channels of the basin. However, its contribution to stream flow cannot fluctuate rapidly because of its very low flow velocity-Provides the dry-weather flow in perennial streams.

Components of Runoff

1. Overland Flow or Surface Runoff

2. Interflow

3. Groundwater Flow or Base Flow:

Categories of Runoff

1. Direct Runoff

2. Base flow

Direct Runoff

It is part of the runoff which enters the stream immediately after the rainfall. It includes surface runoff, prompt interflow and rainfall on the surface of the stream. In the case of snow-melt, the resulting flow entering the stream is also a direct runoff. Direct storm runoff and storm runoff are used to designate direct runoff.

Base Flow

The delayed flow that reaches a stream essentially as groundwater. Delayed interflow is also included under this category. In the annual hydrograph of a perennial stream, the base flow is easily recognized as the slowly decreasing flow of the stream in rainless period.

Runoff Characteristics of Stream

1. Perennial Stream

2. Intermittent Stream

3. Ephemeral stream

Perennial Stream

is one which always carries some flow. There is considerable amount of groundwater flow throughout the year. Even during the dry seasons, the water table will be above the bed off the stream.

Intermittent Stream

has limited contribution from the groundwater. During the wet season the water table is above the stream bed and there is a contribution of the base flow to the stream flow. However, during dry season the water tale drops to a level lower than that of the stream bed and the stream dries up.

Ephemeral Stream

one which does not have any base flow contribution. The annual hydrograph of such a river shows series of short-duration spikes marking flash flows in response to storms. The stream becomes dry soon after the end of the storm flow.

The flow characteristics of a stream depend upon

• The rainfall characteristics, such as magnitude intensity, distribution according to time and space, and its variability.

• Catchment characteristics such as soil, land use/cover, slope, geology, shape and drainage density.

• Climatic factors which influence evapotranspiration.

Infiltrated water

may flow through the matrix of the soil in the inter-granular pores and small structural voids.

macropores

Infiltrated water may also flow through larger voids referred to as

Macropores

include pipes that are open passageways in the soil caused by decaying roots and burrowing animals.

Macropores

also include larger structural voids within the soil matrix that serve as preferential pathways for subsurface flow.

infiltrability

There is a maximum limiting rate at which a soil in a given condition can absorb surface water input. Infiltration capacity is also referred to as

Infiltration excess overland flow mechanism

There is a maximum limiting rate at which a soil in a given condition can absorb surface water input. Infiltration capacity is also referred to as infiltrability. When surface water input exceeds infiltration capacity the excess water accumulates on the soil surface and fills small depressions. Water in depression storage does not directly contribute to overland flow runoff; it either evaporates or infiltrates later.

precipitation

is any produce of condensation of atmospheric water vapour the falls under gravity.

process of formation of precipitaio

Evaporation > Cooling Process > Condensation > Growth of Droplets Process

Rain

These are water droplets mostly size larger than o.5mm in diameter

Drizzle

These are tiny water droplets of size below 0.1mm to 0.5mm which fall with such slow settling rates that they occasionally appear to float.

Snow

It is the type of precipitation which results from sublimation that is water vapors directly changes to ice.

Hail

forms of lumps ice. These hailstones are produced in convective clouds mostly cumulonimbus. ( Very tall and large clouds i.e (5-13km) in appearance)

Snow Pallets

These are sometimes called as soft hail too. These are more crisp and are of 2-5mm of size. Due to their crispness upon hitting the hard ground, they oftenly breaks up.

Sleet

When the rain drops fall through the layer of sub-freezing air near the earths surface, the rain-drop get frozen into ice stage.

Called as Grains of ice.

Types of precipitation

• Orographic Precipitation

• Convective Precipitation

• Cyclonic Precipitation

Orographic Precipitation.

moist air mass get lifted up to higher elevation due to rise of moist air it undergoes cooling, condensation and precipitation. Windward side receives more precipitation than Leeward side.

Convective Precipitation

It is occurred due to if the air parcel is warmer than surrounding air, it start moving in upward direction and empty space near ground is occupied by cold air and precipitation occurred

• It gives High Intensity Rainfall but Short Duration

• Areal Extent of such type of precipitation is small i.e. @10km radius.

Cyclone

occurred due to large low pressure region with circular wind motion.

Cyclonic precipitation

If the two different air masses warm and cold meets each other the warmer air mass start moves in upward direction and start cooling and water vapor in air start condense and clouds are formed which causes precipitation It is also called Frontal Precipitation